MDU RESOURCES GROUP INC, 10-K filed on 2/20/2025
Annual Report
v3.25.0.1
Cover Page - USD ($)
 12 Months Ended
Dec. 31, 2024
Feb. 13, 2025
Jun. 28, 2024
Cover [Abstract]      
Document Type 10-K    
Document Annual Report true    
Document Period End Date Dec. 31, 2024    
Current Fiscal Year End Date --12-31    
Document Transition Report false    
Entity File Number 1-03480    
Entity Registrant Name MDU RESOURCES GROUP, INC.    
Entity Incorporation, State or Country Code DE    
Entity Tax Identification Number 30-1133956    
Entity Address, Address Line One 1200 West Century Avenue    
Entity Address, Address Line Two P.O. Box 5650    
Entity Address, City or Town Bismarck    
Entity Address, State or Province ND    
Entity Address, Postal Zip Code 58506-5650    
City Area Code 701    
Local Phone Number 530-1000    
Title of 12(b) Security Common Stock, par value $1.00 per share    
Trading Symbol MDU    
Security Exchange Name NYSE    
Entity Well-known Seasoned Issuer Yes    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Filer Category Large Accelerated Filer    
Entity Small Business false    
Entity Emerging Growth Company false    
ICFR Auditor Attestation Flag true    
Document Financial Statement Error Correction false    
Entity Shell Company false    
Entity Public Float     $ 5,095,923,531
Entity Common Stock, Shares Outstanding   204,331,170  
Documents Incorporated by Reference
Relevant portions of the registrant's 2025 Proxy Statement, to be filed no later than 120 days from December 31, 2024, are incorporated by reference in Part III, Items 10, 11, 12, 13 and 14 of this Report.
    
Entity Central Index Key 0000067716    
Document Fiscal Year Focus 2024    
Document Fiscal Period Focus FY    
Amendment Flag false    
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Audit Information
 12 Months Ended
Dec. 31, 2024
Audit Information [Abstract]  
Auditor Location Minneapolis, Minnesota
Auditor Name Deloitte & Touche LLP
Auditor Firm ID 34
v3.25.0.1
Consolidated Statements of Income - USD ($)
shares in Thousands, $ in Thousands
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Income Statement [Abstract]      
External operating revenues $ 1,757,978 $ 1,803,352 $ 1,747,298
Operating expenses:      
Purchased natural gas sold 630,403 742,965 757,883
Electric fuel and purchased power 141,148 134,779 119,405
Operation and maintenance 414,491 407,081 379,951
Depreciation and amortization 200,078 190,450 188,560
Taxes, other than income 106,216 103,133 100,629
Total operating expenses 1,492,336 1,578,408 1,546,428
Operating income 265,642 224,944 200,870
Realized gain on tax-free exchange of the retained shares in Knife River 0 186,556 0
Other income 41,367 33,454 3,260
Interest expense 108,347 104,624 80,683
Income before income taxes 198,662 340,330 123,447
Income taxes 17,589 10,213 6,195
Income from continuing operations 181,073 330,117 117,252
Discontinued operations, net of tax 100,035 84,590 250,237
Net income $ 281,108 $ 414,707 $ 367,489
Earnings per share - basic:      
Income from continuing operations (in usd per share) $ 0.89 $ 1.62 $ 0.58
Discontinued operations, net of tax (in usd per share) 0.49 0.42 1.23
Earnings per share - basic (in usd per share) 1.38 2.04 1.81
Earnings per share - diluted:      
Income from continuing operations (in usd per share) 0.88 1.62 0.58
Discontinued operations, net of tax (in usd per share) 0.49 0.41 1.23
Earnings per share - diluted (in usd per share) $ 1.37 $ 2.03 $ 1.81
Weighted average common shares outstanding - basic (in shares) 203,867 203,640 203,358
Weighted average common shares outstanding - diluted (in shares) 204,653 203,938 203,462
v3.25.0.1
Consolidated Statements of Comprehensive Income - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Statement of Comprehensive Income [Abstract]      
Net income $ 281,108 $ 414,707 $ 367,489
Other comprehensive income (loss):      
Reclassification adjustment for loss on derivative instruments included in net income, net of tax of $0, $15 and $177 in 2024, 2023 and 2022, respectively 0 81 413
Postretirement liability adjustment:      
Postretirement liability gains (losses) arising during the period, net of tax of $360, $(201) and $3,965 in 2024, 2023 and 2022, respectively 1,049 (646) 12,007
Amortization of postretirement liability losses included in net periodic benefit credit, net of tax of $145, $78 and $597 in 2024, 2023 and 2022, respectively 432 242 1,819
Reclassification of postretirement liability adjustment from regulatory asset, net of tax of $0, $0 and $(1,086) in 2024, 2023 and 2022, respectively 0 0 (3,265)
Postretirement liability adjustment 1,481 (404) 10,561
Net unrealized gain (loss) on available-for-sale investments:      
Net unrealized gain (loss) on available-for-sale investments arising during the period, net of tax of $23, $46 and $(177) in 2024, 2023 and 2022, respectively 85 173 (667)
Reclassification adjustment for loss on available-for-sale investments included in net income, net of tax of $5, $11 and $31 in 2024, 2023 and 2022, respectively 20 43 114
Net unrealized gain (loss) on available-for-sale investments 105 216 (553)
Other comprehensive income (loss) 1,586 (107) 10,421
Comprehensive income attributable to common stockholders $ 282,694 $ 414,600 $ 377,910
v3.25.0.1
Consolidated Balance Sheets - USD ($)
$ in Thousands
Dec. 31, 2024
Dec. 31, 2023
Current assets:    
Cash, cash equivalents and restricted cash $ 66,904 $ 60,473
Receivables, net 274,303 250,153
Current regulatory assets 215,436 172,492
Inventories 44,940 44,684
Prepayments and other current assets 64,676 66,431
Current assets of discontinued operations 0 769,490
Total current assets 666,259 1,363,723
Noncurrent assets:    
Property, plant and equipment 7,554,063 7,081,267
Less accumulated depreciation and amortization 2,209,771 2,076,375
Net property, plant and equipment 5,344,292 5,004,892
Goodwill 345,736 345,736
Regulatory assets 322,350 447,099
Investments 115,459 112,475
Other 244,722 211,369
Noncurrent assets of discontinued operations 0 347,865
Total noncurrent assets 6,372,559 6,469,436
Total assets 7,038,818 7,833,159
Current liabilities:    
Short-term borrowings 0 95,000
Long-term debt due within one year 161,700 61,319
Accounts payable 150,070 159,975
Regulatory liabilities due within one year 137,167 70,761
Taxes payable 43,372 49,553
Dividends payable 26,511 25,461
Accrued compensation 35,264 40,792
Other accrued liabilities 124,514 129,592
Current liabilities of discontinued operations 0 443,280
Total current liabilities 678,598 1,075,733
Noncurrent liabilities:    
Long-term debt 2,130,910 2,104,904
Deferred income taxes 441,320 452,336
Regulatory liabilities 459,170 521,050
Asset retirement obligations 406,351 384,371
Other 231,895 209,882
Noncurrent liabilities of discontinued operations 0 179,650
Total noncurrent liabilities 3,669,646 3,852,193
Commitments and contingencies
Stockholders' equity:    
Common stock Authorized - 500,000,000 shares, $1.00 par value Shares issued - 203,934,578 at December 31, 2024 and 203,689,090 at December 31, 2023 203,935 203,689
Other paid-in capital 1,473,738 1,466,235
Retained earnings 1,029,699 1,253,693
Accumulated other comprehensive loss (16,798) (18,384)
Total stockholders' equity 2,690,574 2,905,233
Total liabilities and stockholders' equity $ 7,038,818 $ 7,833,159
v3.25.0.1
Consolidated Statements of Equity - USD ($)
$ in Thousands
Total
Common Stock
Other Paid-in Capital
Retained Earnings
Total Accumulated Other Comprehensive Loss
Treasury Stock
Common stock, beginning balance (in shares) at Dec. 31, 2021   203,889,661        
Beginning balance at Dec. 31, 2021 $ 3,382,874 $ 203,889 $ 1,461,205 $ 1,762,410 $ (41,004) $ (3,626)
Treasury stock, common, beginning balance (in shares) at Dec. 31, 2021           (538,921)
Increase (Decrease) in Stockholders' Equity [Roll Forward]            
Net income 367,489     367,489    
Other comprehensive income (loss) 10,421       10,421  
Dividends declared on common stock (178,761)     (178,761)    
Employee stock-based compensation 10,254   10,254      
Repurchase of common stock (in shares)           (266,821)
Repurchase of common stock (7,399)         $ (7,399)
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings (in shares)           266,821
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings (4,904)   (12,303)     $ 7,399
Issuance of common stock (in shares)   273,153        
Issuance of common stock 7,155 $ 274 6,881      
Common stock, ending balance (in shares) at Dec. 31, 2022   204,162,814        
Ending balance at Dec. 31, 2022 3,587,129 $ 204,163 1,466,037 1,951,138 (30,583) $ (3,626)
Treasury stock, common, ending balance (in shares) at Dec. 31, 2022           (538,921)
Increase (Decrease) in Stockholders' Equity [Roll Forward]            
Net income 414,707     414,707    
Other comprehensive income (loss) (107)       (107)  
Dividends declared on common stock (142,033)     (142,033)    
Employee stock-based compensation 6,781   6,781      
Repurchase of common stock (in shares)           (153,622)
Repurchase of common stock (4,811)         $ (4,811)
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings (in shares)           153,622
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings (3,040)   (7,851)     $ 4,811
Separation of Knife River and Everus (in shares)   (538,921)       (538,921)
Separation of Knife River and Everus (954,726) $ (539)   (970,119) 12,306 $ 3,626
Issuance of common stock (in shares)   65,197        
Issuance of common stock $ 1,333 $ 65 1,268      
Common stock, ending balance (in shares) at Dec. 31, 2023 203,689,090 203,689,090        
Ending balance at Dec. 31, 2023 $ 2,905,233 $ 203,689 1,466,235 1,253,693 (18,384) $ 0
Treasury stock, common, ending balance (in shares) at Dec. 31, 2023           0
Increase (Decrease) in Stockholders' Equity [Roll Forward]            
Net income 281,108     281,108    
Other comprehensive income (loss) 1,586       1,586  
Dividends declared on common stock (104,786)     (104,786)    
Employee stock-based compensation 9,572   9,572      
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings (in shares)   199,147        
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings (2,623) $ 199 (2,822)      
Separation of Knife River and Everus (400,316)     (400,316)    
Issuance of common stock (in shares)   46,341        
Issuance of common stock $ 800 $ 47 753      
Common stock, ending balance (in shares) at Dec. 31, 2024 203,934,578 203,934,578        
Ending balance at Dec. 31, 2024 $ 2,690,574 $ 203,935 $ 1,473,738 $ 1,029,699 $ (16,798) $ 0
Treasury stock, common, ending balance (in shares) at Dec. 31, 2024           0
v3.25.0.1
Consolidated Statements of Cash Flows - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Operating activities:      
Net income $ 281,108 $ 414,707 $ 367,489
Income from discontinued operations, net of tax 100,035 84,590 250,237
Income from continuing operations 181,073 330,117 117,252
Adjustments to reconcile net income to net cash provided by operating activities:      
Depreciation and amortization 200,078 190,450 188,560
Deferred income taxes (16,078) (1,309) 20,187
Provision for credit losses 6,558 7,422 5,409
Amortization of debt issuance costs 1,828 1,013 885
Employee stock-based compensation costs 8,423 5,505 7,913
Pension and postretirement benefit plan net periodic benefit credit (3,837) (5,380) (7,323)
Unrealized (gains) losses on investments (5,942) (7,431) 10,119
(Gains) losses on sales of assets (857) (347) 15
Gain on tax-free exchange of the retained shares in Knife River 0 (186,556) 0
Changes in current assets and liabilities, net of acquisitions:      
Receivables (30,310) 79,111 (91,193)
Inventories 246 (21,729) 243
Other current assets 80,977 (48,492) 14,522
Accounts payable (443) (87,209) 84,547
Other current liabilities (5,252) 73,365 (26,873)
Pension and postretirement benefit plan contributions (3,000) (7,643) (81)
Other noncurrent changes (1,651) (15,554) (2,567)
Net cash provided by continuing operations 411,813 305,333 321,615
Net cash provided by discontinued operations 90,505 27,294 188,449
Net cash provided by operating activities 502,318 332,627 510,064
Investing activities:      
Capital expenditures (522,824) (484,136) (442,582)
Net proceeds from sale or disposition of property 691 260 3
Cost of removal, net of salvage value (5,539) 1,170 (11,779)
Investments (5,155) (2,423) (2,571)
Proceeds from investment cost basis withdrawal 9,000 20,000 0
Net cash used in continuing operations (523,827) (465,129) (456,929)
Net cash used in discontinued operations (28,858) (75,662) (181,952)
Net cash used in investing activities (552,685) (540,791) (638,881)
Financing activities:      
Issuance of short-term borrowings 0 810,000 11,500
Repayment of short-term borrowings (95,000) (433,901) 0
Issuance of long-term debt 308,600 594,700 214,969
Repayment of long-term debt (182,135) (568,883) (38,764)
Debt issuance costs (2,456) (2,521) (1,129)
Costs of issuance of common stock (50) 0 (150)
Dividends paid (102,939) (161,316) (176,915)
Repurchase of common stock 0 (4,811) (7,399)
Tax withholding on stock-based compensation (2,623) (3,040) (4,904)
Net cash (used in) provided by continuing operations (76,603) 230,228 (2,792)
Net cash provided by (used in) discontinued operations 116,899 (25,606) 157,965
Net cash provided by financing activities 40,296 204,622 155,173
(Decrease) increase in cash, cash equivalents and restricted cash (10,071) (3,542) 26,356
Cash, cash equivalents and restricted cash - beginning of year 76,975 [1] 80,517 [1] 54,161
Cash, cash equivalents and restricted cash - end of year [1] $ 66,904 $ 76,975 $ 80,517
[1]
*Includes cash of discontinued operations of $16.5 million and $9.7 million for the years ended December 31, 2023 and 2022, respectively.
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Consolidated Statements of Comprehensive Income (Parenthetical) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Statement of Comprehensive Income [Abstract]      
Reclassification adjustment for loss on derivative instruments included in net income, tax $ 0 $ 15 $ 177
Postretirement liability gains (losses) arising during the period, tax 360 (201) 3,965
Amortization of postretirement liability losses included in net periodic benefit credit, tax 145 78 597
Reclassification of postretirement liability adjustment from regulatory asset, tax 0 0 (1,086)
Net unrealized loss on available-for-sale investments arising during the period, tax 23 46 (177)
Reclassification adjustment for loss on available-for-sale investments included in net income, tax $ 5 $ 11 $ 31
v3.25.0.1
Consolidated Balance Sheets (Parenthetical) - $ / shares
Dec. 31, 2024
Dec. 31, 2023
Statement of Financial Position [Abstract]    
Common stock, authorized (in shares) 500,000,000 500,000,000
Common stock, par value per share (in usd per share) $ 1.00 $ 1.00
Common stock, issued (in shares) 203,934,578 203,689,090
v3.25.0.1
Consolidated Statements of Cash Flows (Parenthetical) - USD ($)
$ in Millions
Dec. 31, 2023
Dec. 31, 2022
Statement of Cash Flows [Abstract]    
Disposal group, including discontinued operation, cash and cash equivalents $ 16.5 $ 9.7
v3.25.0.1
Basis of Presentation
 12 Months Ended
Dec. 31, 2024
Accounting Policies [Abstract]  
Basis of Presentation Basis of Presentation
The consolidated financial statements of the Company include the accounts of the following businesses: electric, natural gas distribution, pipeline and other. For further descriptions of the Company's businesses, see Note 17.
On May 31, 2023, the Company completed the separation of Knife River, formerly the construction materials and contracting segment, resulting in Knife River becoming an independent, publicly-traded company. The Company's board of directors approved the distribution of approximately 90 percent of the issued and outstanding shares of Knife River to the Company's stockholders. Stockholders of the Company received one share of Knife River common stock for every four shares of the Company's common stock held on May 22, 2023, the record date for the distribution. The Company retained approximately 10 percent or 5.7 million shares of Knife River common stock immediately following the separation, which were disposed of in a tax-free exchange in November 2023. The separation of Knife River was a tax-free spinoff transaction to the Company's stockholders for U.S. federal income tax purposes, except for cash received in lieu of fractional shares.
On October 31, 2024, the Company completed the separation of Everus, its construction services business, resulting in Everus becoming an independent, publicly-traded company. The Company's board of directors approved the distribution of all the outstanding shares of Everus common stock to the Company's stockholders. Stockholders of the Company received one share of Everus common stock for every four shares of the Company's common stock held as of the close of business on October 21, 2024, the record date for the distribution. The separation of Everus was a tax-free spinoff transaction to the Company's stockholders for U.S. federal income tax purposes, except for cash received in lieu of fractional shares.
The Company's consolidated financial statements and accompanying notes for the current and prior periods have been restated to present the results of operations and the assets and liabilities of Knife River and Everus as discontinued operations, other than certain corporate overhead costs of the Company historically allocated to Knife River and Everus, which are reflected in Other. Also included in discontinued operations in the Consolidated Statements of Income are the supporting activities of Fidelity and certain interest expense related to financing activity associated with the Knife River and Everus separations. The assets and liabilities of the Company's discontinued operations are included in current assets of discontinued operations, noncurrent assets of discontinued operations, current liabilities of discontinued operations and noncurrent liabilities of discontinued operations on the Consolidated Balance Sheets. Unless otherwise indicated, the amounts presented in the accompanying notes to the consolidated financial statements relate to the Company's continuing operations. For more information on discontinued operations, see Note 3.
Additionally, certain amounts recorded in prior year financial statements have been reclassified to conform to the current year presentation. The Company has reclassified $26.9 million and $27.4 million of transmission-related expenses from operation and maintenance to electric fuel and purchased power for the years ended December 31, 2023 and 2022, respectively, in the Consolidated Statements of Income. These transmission-related expenses are an integral component of the cost of electricity sold to customers and therefore, more appropriately reflected in electric fuel and purchased power than operation and maintenance expense. These reclassifications had no effect on previously reported results of operations or cash flows.
Management has also evaluated the impact of events occurring after December 31, 2024, up to the date of issuance of these consolidated financial statements on February 20, 2025, that would require recognition or disclosure in the financial statements.
Principles of consolidation
The consolidated financial statements were prepared in accordance with GAAP and include the accounts of the Company and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation, except for certain transactions related to regulated operations in accordance with GAAP. For more information on intercompany revenues, see Note 17.
The statements also include the Company's ownership interests in the assets, liabilities and expenses of jointly owned electric transmission and generating facilities. See Note 19 for additional information.
Use of estimates
The preparation of financial statements in conformity with GAAP requires the Company to make estimates and assumptions that affect the reported amounts of assets and liabilities, and disclosure of contingent assets and liabilities, at the date of the financial statements, as well as the reported amounts of revenues and expenses during the reporting period. Estimates are used for items such as long-lived assets and goodwill; property depreciable lives; tax provisions; revenue recognized using the cost-to-cost measure of progress for contracts; expected credit losses; environmental and other loss contingencies; regulatory assets expected to be recovered in rates charged to customers; costs on construction contracts; unbilled revenues; actuarially determined benefit costs; asset retirement obligations; lease classification; present value of right-of-use assets and lease liabilities; and the valuation of stock-based compensation. As additional information becomes available, or actual amounts are determinable, the recorded estimates are revised. Consequently, operating results can be affected by revisions to prior accounting estimates.
v3.25.0.1
Significant Accounting Policies
 12 Months Ended
Dec. 31, 2024
Accounting Policies [Abstract]  
Significant Accounting Policies Significant Accounting Policies
New accounting standards
The following table provides a brief description of the accounting pronouncements applicable to the Company and the potential impact on its financial statements and/or disclosures:
StandardDescriptionEffective dateImpact on financial statements/disclosures
Recently adopted accounting standards
ASU 2022-06 - Reference Rate Reform: Deferral of Sunset DateIn December 2022, the FASB included a sunset provision within ASC 848 based on expectations of when LIBOR would cease being published. At the time ASU 2020-04 was issued, the UK Financial Conduct Authority had established its intent to cease overnight tenors of LIBOR after December 31, 2021. In March 2021, the UK Financial Conduct Authority announced that the intended cessation date of the overnight tenors of LIBOR would be June 30, 2023 which is beyond the current sunset date of ASC 848. The amendments in this Update defer the sunset date of ASC 848 from December 31, 2022 to December 31, 2024, after which entities will no longer be permitted to apply the relief in ASC 848.December 31, 2024
The Company has updated its credit agreements to include language regarding the successor or alternate rate to LIBOR. The Company did not have a material impact on its results of operations, financial position, cash flows or disclosures.
ASU 2023-07 Segment Reporting - Improvements to Reportable Segment Disclosures
In November 2023, the FASB issued guidance on improving financial reporting by requiring disclosure of incremental segment information, primarily through enhanced disclosures about significant segment expenses, on an annual and interim basis for all public entities to enable investors to develop more decision-useful financial analyses.
December 31, 2024
The Company identified and updated disclosures to ensure compliance with the new guidance. See Note 17.
Recently issued accounting standards not yet adopted
ASU 2023-09 Income Taxes - Improvements to Income Tax Disclosures an Amendment, December 2023
In December 2023, the FASB issued guidance to address investors requests for more transparency about income tax information through improvements to income tax disclosures primarily related to the rate reconciliation and income taxes paid information and effectiveness of income tax disclosures.
Effective for annual reporting periods beginning after 2024 on a prospective basis.
The Company is currently evaluating the impact the guidance will have on its disclosures for the year ended December 31, 2025.
ASU 2024-01 Compensation - Stock Compensation
In March 2024, the FASB issued Improvements to GAAP through an example to demonstrate application of the scope of paragraph 718-10-15-3 to determine whether profits interest and similar awards should be accounted in Compensation - Stock Compensation.
Effective for fiscal year beginning after December 15, 2024.The Company is currently evaluating the impact the guidance will have on its disclosures for the year ended December 31, 2025.
ASU 2024-03 Disaggregation of Income Statement Expenses
In November 2024, the FASB issued guidance to improve the disclosures about a public business entity's expenses and address requests from investors for more detailed information about the types of expenses (including purchases of inventory, employee compensation, depreciation, amortization, and depletion) in commonly presented expense captions (such as cost of sales, selling, general, and administrative; and research and development).
Effective for annual reporting periods beginning after December 15, 2026, and interim reporting periods beginning after December 15, 2027.
The Company is currently evaluating the impact the guidance will have on its disclosures for the year ended December 31, 2027.
Cash, cash equivalents and restricted cash
The Company considers all highly liquid investments purchased with an original maturity of three months or less to be cash equivalents. Restricted cash represents deposits held by the Company’s captive insurance company that is required by state insurance regulations to remain in the captive insurance company. The Company had restricted cash of $16.7 million and $13.2 million at December 31, 2024 and 2023, respectively.
Revenue recognition
Revenue is recognized when a performance obligation is satisfied by transferring control over a product or service to a customer. Revenue is measured based on consideration specified in a contract with a customer and excludes any sales incentives and amounts collected on behalf of third parties. The Company is considered an agent for certain taxes collected from customers. As such, the Company presents revenues net of these taxes at the time of sale to be remitted to governmental authorities, including sales and use taxes.
The electric and natural gas distribution segments generate revenue from the sales of electric and natural gas products and services, which includes retail and transportation services. These segments establish a customer's retail or transportation service account based on the customer's application/contract for service, which indicates approval of a contract for service. The contract identifies an obligation to provide service in exchange for delivering or standing ready to deliver the identified commodity; and the customer is obligated to pay for the service as provided in the applicable tariff. The product sales are based on a fixed rate that includes a base and per-unit rate, which are included in approved tariffs as determined by state or federal regulatory agencies. The quantity of the commodity consumed or transported determines the total per-unit revenue. The service provided, along with the product consumed or transported, are a single performance obligation because both are required in combination to successfully transfer the contracted product or service to the customer. Revenues are recognized over time as customers receive and consume the products and services. The method of measuring progress toward the completion of the single performance obligation is on a per-unit output method basis, with revenue recognized based on the direct measurement of the value to the customer of the goods or services transferred to date. For contracts governed by the Company’s utility tariffs, amounts are billed monthly with the amount due between 15 and 22 days of receipt of the invoice depending on the applicable state’s tariff. For other contracts not governed by tariff, payment terms are net 30 days. At this time, the segment has no material obligations for returns, refunds or other similar obligations.
The pipeline segment generates revenue from providing natural gas transportation and underground storage services, as well as other energy-related services to both third parties and internal customers, largely the natural gas distribution segment. The pipeline segment establishes a contract with a customer based upon the customer’s request for firm or interruptible natural gas transportation or storage service(s). The contract identifies an obligation for the segment to provide the requested service(s) in exchange for consideration from the customer over a specified term. Depending on the type of service(s) requested and contracted, the service provided may include transporting or storing an identified quantity of natural gas and/or standing ready to deliver or store an identified quantity of natural gas. Natural gas transportation and storage revenues are based on fixed rates, which may include reservation fees and/or per-unit commodity rates. The services provided by the segment are generally treated as single performance obligations satisfied over time simultaneous to when the service is provided and revenue is recognized. Rates for the segment’s regulated services are based on its FERC approved tariff or customer negotiated rates, and rates for its non-regulated services are negotiated with its customers and set forth in the contract. For contracts governed by the company’s tariff, amounts are billed on or before the ninth business day of the following month and the amount is due within 12 days of receipt of the invoice. For other contracts not governed by the tariff, payment terms are net 30 days. At this time, the segment has no material obligations for returns, refunds or other similar obligations.
The Company recognizes all other revenues when services are rendered or goods are delivered.
Legal costs
The Company generally expenses external legal fees as they are incurred unless it has specific circumstances to defer, such as probable recovery in a rate proceeding.
Receivables and allowance for expected credit losses
Receivables consist primarily of trade receivables from the sale of goods and services net of expected credit losses. The Company's trade receivables are all due in 12 months or less. The total balance of receivables past due 90 days or more was $3.6 million and $3.7 million at December 31, 2024 and 2023, respectively.
The Company's expected credit losses are determined through a review using historical credit loss experience, changes in asset specific characteristics, current conditions and reasonable and supportable future forecasts, among other specific account data, and is performed at least quarterly. The Company develops and documents its methodology to determine its allowance for expected credit losses at each of its reportable business segments. Risk characteristics used by the business segments may include customer mix, knowledge of customers and general economic conditions of the various local economies, among others. Specific account balances are written off when management determines the amounts to be uncollectible. Management has reviewed the balance reserved through the allowance for expected credit losses and believes it is reasonable.
Details of the Company's expected credit losses were as follows:
ElectricNatural gas
distribution		PipelineTotal
 (In thousands)
At December 31, 2022
$375 $1,615 $2 $1,992 
Current expected credit loss provision
1,645 5,777 — 7,422 
Less write-offs charged against the allowance1,994 7,355 2 9,351 
Credit loss recoveries collected388 1,152 — 1,540 
At December 31, 2023414 1,189 — 1,603 
Current expected credit loss provision1,891 4,667 — 6,558 
Less write-offs charged against the allowance2,218 5,709 — 7,927 
Credit loss recoveries collected386 1,219 — 1,605 
At December 31, 2024$473 $1,366 $— $1,839 
Receivables also consist of accrued unbilled revenue representing revenues recognized in excess of amounts billed. Accrued unbilled revenue at MDU Energy Capital was $143.2 million and $132.0 million at December 31, 2024 and 2023, respectively.
Inventories and natural gas in storage            
Natural gas in storage is generally valued at lower of cost or market using the last-in, first-out method or lower of cost or net realizable value using the average cost or first-in, first-out method. The majority of all other inventories are valued at the lower of cost or net realizable value using the average cost method. The portion of the cost of natural gas in storage expected to be used within 12 months was included in inventories. Inventories at December 31 consisted of:
 20242023
 (In thousands)
Natural gas in storage (current)$40,073 $39,377 
Fuel stock4,867 5,307 
Total$44,940 $44,684 
The remainder of natural gas in storage, which largely represents the cost of gas required to maintain pressure levels for normal operating purposes, was included in noncurrent assets - other and was $48.5 million at both December 31, 2024 and 2023, respectively.
Property, plant and equipment
Additions to property, plant and equipment are recorded at cost. When regulated assets are retired, or otherwise disposed of in the ordinary course of business, the original cost of the asset is charged to accumulated depreciation. With respect to the retirement or disposal of all other assets, the resulting gains or losses are recognized as a component of income.
The Company is permitted to capitalize AFUDC on regulated construction projects and to include such amounts in rate base when the related facilities are placed in service. In addition, the Company capitalizes interest, when applicable, on certain contracting services projects associated with its other operations. The amount of AFUDC for the years ended December 31 was as follows:
202420232022
(In thousands)
AFUDC - borrowed$10,964 $10,035 $2,236 
AFUDC - equity$2,251 $1,894 $2,165 
Generally, property, plant and equipment are depreciated on a straight-line basis over the average useful lives of the assets.
The Company collects removal costs for certain plant assets in regulated utility rates. These amounts are recorded as regulatory liabilities on the Consolidated Balance Sheets.
Impairment of long-lived assets, excluding goodwill
The Company reviews the carrying values of its long-lived assets, whenever events or changes in circumstances indicate that such carrying values may not be recoverable. The Company tests long-lived assets for impairment at a level significantly lower than that of goodwill impairment testing. Long-lived assets or groups of assets that are evaluated for impairment at the lowest level of largely independent identifiable cash flows at an individual operation or group of operations collectively serving a local market. The determination of whether an impairment has occurred is based on an estimate of undiscounted future cash flows attributable to the assets, compared to the carrying value of the assets. If impairment has occurred, the amount of the impairment recognized is determined by estimating the fair value of the assets and recording a loss if the carrying value is greater than the fair value. The impairments are recorded in operation and maintenance expense on the Consolidated Statements of Income.
No impairment losses were recorded in 2024, 2023 or 2022. Unforeseen events and changes in circumstances could require the recognition of impairment losses at some future date.
Regulatory assets and liabilities
The Company is subject to various state and federal agency regulations. The accounting policies followed by the Company are generally subject to the Uniform System of Accounts of the FERC as well as the provisions of ASC 980 - Regulated Operations. These accounting policies differ in some respects from those used by the Company's non-regulated businesses.
The Company accounts for certain income and expense items under the provisions of regulatory accounting, which requires the Company to defer as regulatory assets or liabilities certain items that would have otherwise been reflected as expense or income, respectively. The Company records regulatory assets or liabilities at the time the Company determines the amounts to be recoverable in current or future rates. Regulatory assets and liabilities are being amortized consistently with the regulatory treatment established by the FERC and the applicable state public service commission. See Note 6 for more information regarding the nature and amounts of these regulatory deferrals.
Goodwill
Goodwill represents the excess of the purchase price over the fair value of identifiable net tangible and intangible assets acquired in a business combination. Goodwill is required to be tested for impairment annually, which the Company completes in the fourth quarter, or more frequently if events or changes in circumstances indicate that goodwill may be impaired.
The Company has determined that the reporting units for its goodwill impairment test are its operating segments, or components of an operating segment, that constitute a business for which discrete financial information is available and for which segment management regularly reviews the operating results. As of December 31, 2024, the only operating segment with goodwill was the natural gas distribution segment. For more information on the Company's operating segments, see Note 17.
Goodwill impairment, if any, is measured by comparing the fair value of each reporting unit to its carrying value. If the fair value of a reporting unit exceeds its carrying value, the goodwill of the reporting unit is not impaired. If the carrying value of a reporting unit exceeds its fair value, the Company must record an impairment loss for the amount that the carrying value of the reporting unit, including goodwill, exceeds the fair value of the reporting unit. For the years ended December 31, 2024, 2023 and 2022, there were no impairment losses recorded.
Investments
The Company's investments include the cash surrender value of life insurance policies, insurance contracts, mortgage-backed securities and U.S. Treasury securities. The Company measures its investment in the insurance contracts at fair value with any unrealized gains and losses recorded on the Consolidated Statements of Income. The Company has not elected the fair value option for its mortgage-backed securities and U.S. Treasury securities and, as a result, the unrealized gains and losses on these investments are recorded in accumulated other comprehensive loss. For more information, see Notes 9 and 18.
Variable interest entities
The Company evaluates its arrangements and contracts with other entities to determine if they are VIEs and if so, if the Company is the primary beneficiary. GAAP provides a framework for identifying VIEs and determining when a company should include the assets, liabilities, noncontrolling interest and results of activities of a VIE in its consolidated financial statements.
A VIE should be consolidated if a party with an ownership, contractual or other financial interest in the VIE (a variable interest holder) has the power to direct the VIE's most significant activities and the obligation to absorb losses or right to receive benefits of the VIE that could be significant to the VIE. A variable interest holder that consolidates the VIE is called the primary beneficiary. Upon consolidation, the primary beneficiary generally must initially record all of the VIE's assets, liabilities and noncontrolling interests at fair value and subsequently account for the VIE as if it were consolidated.
The Company's evaluation of whether it qualifies as the primary beneficiary of a VIE involves significant judgments, estimates and assumptions and includes a qualitative analysis of the activities that most significantly impact the VIE's economic performance and whether the Company has the power to direct those activities, the design of the entity, the rights of the parties and the purpose of the arrangement.
Derivative instruments
The Company enters into commodity price derivative contracts in order to minimize the price volatility associated with customer natural gas costs at its natural gas distribution segment. These derivatives are not designated as hedging instruments and are recorded in the Consolidated Balance Sheets at fair value. Changes in the fair value of these derivatives along with any contract settlements are recorded each period in regulatory assets or liabilities in accordance with regulatory accounting. The Company does not enter into any derivatives for trading or other speculative purposes.
The Company did not have any material commodity price derivative contracts at December 31, 2024 or 2023.
Leases
Lease liabilities and their corresponding right-of-use assets are recorded based on the present value of lease payments over the expected lease term. The Company recognizes leases with an original lease term of 12 months or less in income on a straight-line basis over the term of the lease and does not recognize a corresponding right-of-use asset or lease liability. The Company determines the lease term based on the non-cancelable and cancelable periods in each contract. The non-cancelable period consists of the term of the contract that is legally enforceable and cannot be canceled by either party without incurring a significant penalty. The cancelable period is determined by various factors that are based on who has the right to cancel a contract. If only the lessor has the right to cancel the contract, the Company will assume the contract will continue. If the lessee is the only party that has the right to cancel the contract, the Company looks to asset, entity and market-based factors. If both the lessor and the lessee have the right to cancel the contract, the Company assumes the contract will not continue.
The discount rate used to calculate the present value of the lease liabilities is based upon the implied rate within each contract. If the rate is unknown or cannot be determined, the Company uses an incremental borrowing rate, which is determined by the length of the contract, asset class and the Company's borrowing rates, as of the commencement date of the contract.
Asset retirement obligations
The Company records the fair value of a liability for an asset retirement obligation in the period in which it is incurred. When the liability is initially recorded, the Company capitalizes a cost by increasing the carrying amount of the related long-lived asset. Over time, the liability is accreted to its present value each period and the capitalized cost is depreciated over the useful life of the related asset. Upon settlement of the liability, the Company either settles the obligation for the recorded amount or incurs a gain or loss at its non-regulated operations or incurs a regulatory asset or liability at its regulated operations.
Stock-based compensation
The Company determines compensation expense for stock-based awards based on the estimated fair values at the grant date and recognizes the related compensation expense over the vesting period. The Company uses the straight-line amortization method to recognize compensation expense related to RSUs, which only has a service condition. This method recognizes stock compensation expense on a straight-line basis over the requisite service period for the entire award. The Company recognized compensation expense related to PSAs that vest based on performance metrics and service conditions on a straight-line basis over the service period. Inception-to-date expense was adjusted based upon the determination of the potential achievement of the performance target at each reporting date. The Company recognized compensation expense related to PSAs with market-based performance metrics on a straight-line basis over the requisite service period. Outstanding PSAs were converted to RSUs in connection with the completed separation of Knife River through the spinoff.
The Company records the compensation expense for PSAs using an estimated forfeiture rate. The estimated forfeiture rate is calculated based on an average of actual historical forfeitures. The Company also performs an analysis of any known factors at the time of the calculation to identify any necessary adjustments to the average historical forfeiture rate. At the time actual forfeitures become more than estimated forfeitures, the Company records compensation expense using actual forfeitures.
Earnings per share
Basic earnings per share is computed by dividing net income by the weighted average number of shares of common stock outstanding during the year. Diluted earnings per share is computed by dividing net income by the total of the weighted average number of shares of common stock outstanding during the year, plus the effect of nonvested performance share awards and restricted stock units. Common stock outstanding includes issued shares less shares held in treasury. As a result of the 2023 Knife River separation, the Company retained legal ownership of 538,921 shares of the Company's common stock that were historically owned by a subsidiary of Knife River and recorded in Treasury stock at cost. Following the separation, the 538,921 treasury shares were retired. The 538,921 shares of treasury stock did not have an impact on weighted-average shares outstanding, as they were not outstanding prior to being retired. Net income was the same for both the basic and diluted earnings per share calculations. A reconciliation of the weighted average common shares outstanding used in the basic and diluted earnings per share calculations follows:
2024 2023 2022 
(In thousands, except per share amounts)
Weighted average common shares outstanding - basic203,867 203,640 203,358 
Effect of dilutive performance share awards786 298 104 
Weighted average common shares outstanding - diluted204,653 203,938 203,462 
Earnings per share - basic:
Income from continuing operations
$.89 $1.62 $.58 
Discontinued operations, net of tax
.49 .42 1.23 
Earnings per share - basic
$1.38 $2.04 $1.81 
Earnings per share - diluted:
Income from continuing operations
$.88 $1.62 $.58 
Discontinued operations, net of tax
.49 .41 1.23 
Earnings per share - diluted
$1.37 $2.03 $1.81 
Shares excluded from the calculation of diluted earnings per share— — 14 
Dividends declared per common share
$.5100 $.6950 $.8750 
Income taxes
The Company provides deferred federal and state income taxes on all temporary differences between the book and tax basis of the Company's assets and liabilities by using enacted tax rates in effect for the year in which the differences are expected to reverse. The effect of a change in tax rates on deferred tax assets and liabilities is recognized in income in the period that includes the enactment date. Excess deferred income tax balances associated with the Company's rate-regulated activities have been recorded as regulatory liabilities. These regulatory liabilities are expected to be reflected as a reduction in future rates charged to customers in accordance with applicable regulatory procedures.
The Company uses the deferral method of accounting for investment tax credits and amortizes the credits on regulated electric and natural gas distribution plant over various periods that conform to the ratemaking treatment prescribed by the applicable state public service commissions.
The Company records uncertain tax positions in accordance with accounting guidance on accounting for income taxes on the basis of a two-step process in which (1) the Company determines whether it is more-likely-than-not that the tax position will be sustained on the basis of the technical merits of the position and (2) for those tax positions that meet the more-likely-than-not recognition threshold, the Company recognizes the largest amount of the tax benefit that is more than 50 percent likely to be realized upon ultimate settlement with the related tax authority. Tax positions that do not meet the more-likely-than-not criteria are reflected as a tax liability. The Company recognizes interest and penalties accrued related to unrecognized tax benefits in income taxes.
v3.25.0.1
Discontinued Operations
 12 Months Ended
Dec. 31, 2024
Discontinued Operations and Disposal Groups [Abstract]  
Discontinued Operations Discontinued Operations
On May 31, 2023, the Company completed the separation of Knife River, its former construction materials and contracting segment, into a new independent publicly-traded company. The separation was achieved through the Company's pro-rata distribution of approximately 90 percent of the outstanding shares of Knife River to the Company's common stockholders. To effect the separation, the Company distributed to its stockholders one share of Knife River common stock for every four shares of the Company's common stock held on May 22, 2023, the record date for the distribution, with the Company retaining approximately 10 percent, or 5.7 million shares of Knife River common stock immediately following the separation. In November 2023, the Company completed the tax-free exchange of its retained shares and recognized a gain of $186.6 million, which was reflected in continuing operations because the Company did not have continuing significant involvement in Knife River. The separation of Knife River was a tax-free spinoff transaction to the Company's stockholders for U.S. federal income tax purposes, except for cash received in lieu of fractional shares.
On October 31, 2024, the Company completed the separation of Everus, its former construction services segment, into a new independent, publicly-traded company. The Company's board of directors approved the distribution of all the outstanding shares of Everus common stock to the Company's stockholders. Stockholders of the Company received one share of Everus common stock for every four shares of the Company's common stock held as of the close of business on October 21, 2024, the record date for the distribution. The separation of Everus was a tax-free spinoff transaction to the Company's stockholders for U.S. federal income tax purposes, except for cash received in lieu of fractional shares.
As a result of the separations, the historical results of operations are shown in discontinued operations, net of tax, except for allocated general corporate overhead costs of the Company, which did not meet the criteria for discontinued operations. The Company’s consolidated financial statements and accompanying notes for prior periods have been restated. For the comparative periods, Everus' operations are only reflected through October 2024 compared to the full year in 2023 and 2022 and Knife River's operations are only reflected through May 2023 compared to the full year in 2022.
On April 25, 2023, Knife River issued $425.0 million of senior notes, pursuant to an indenture, due in 2031 to qualified institutional buyers. Knife River also entered into a new credit agreement which provided a revolving credit facility in an initial amount of up to $350.0 million and a senior secured term loan facility in an amount up to $275.0 million. The net proceeds from the notes offering, revolving credit facility and the term loan were used to repay $825.0 million of Knife River's intercompany obligations owed to Centennial. Centennial used the entirety of these proceeds from Knife River to repay a portion of its existing third-party indebtedness.
As a result of the separation of Knife River, the Company retained legal ownership of 538,921 shares of the Company's common stock that were historically owned by a subsidiary of Knife River and recorded in Treasury stock at cost. Following the separation of Knife River, the 538,921 treasury shares were retired.
The Company provided to Knife River and Knife River provided to the Company transition services in accordance with the transition services agreement entered into on May 31, 2023. For the twelve months ended December 31, 2024 and 2023, the Company received $1.5 million and $2.9 million, respectively; and paid $159,000 and $823,000, respectively, for these related activities. All transition services were completed as of October 2024.
The Company provided and will provide to Everus and Everus provided and will provide to the Company transition services in accordance with the transition services agreement entered into on October 31, 2024. For the twelve months ended December 31, 2024, the Company received $727,000; and paid $47,000, for these related activities. The majority of the transition services are expected to be provided for a period of approximately eighteen months, however, no longer than two years after the separation.
Separation related costs of $41.7 million, $58.6 million and $11.5 million net of tax, were incurred during the twelve months ended December 31, 2024, 2023 and 2022, respectively. Certain separation costs incurred are presented in discontinued operations, net of tax in the Consolidated Statements of Income. These charges primarily relate to transaction and third-party support costs, one-time business separation fees and related tax charges.
The Company had no assets or liabilities related to the discontinued operations of Knife River on its balance sheet as of December 31, 2024 and 2023. The carrying amounts of the major classes of assets and liabilities related to the discontinued operations of Everus included in the Company’s Consolidated Balance Sheet at December 31, 2023 were as follows:
December 31, 2023
Assets(In Thousands)
Current assets:
Cash and cash equivalents$16,501 
Receivables, net692,629 
Inventories42,709 
Prepayments and other current assets17,651 
Total current assets of discontinued operations769,490 
Noncurrent assets:
Net property, plant and equipment116,018 
Goodwill143,224 
Other intangible assets, net2,004 
Investments11,760 
Operating lease right-of-use assets53,232 
Other21,627 
Total noncurrent assets of discontinued operations347,865 
Total assets of discontinued operations$1,117,355 
Liabilities
Current liabilities:
Accounts payable$315,240 
Taxes payable8,557 
Accrued compensation44,721 
Operating lease liabilities due within one year21,143 
Other accrued liabilities53,619 
Total current liabilities of discontinued operations443,280 
Noncurrent liabilities:
Long-term debt132,000 
Deferred income taxes6,212 
Operating lease liabilities32,504 
Other8,934 
Total noncurrent liabilities of discontinued operations179,650 
Total liabilities of discontinued operations$622,930 
The reconciliation of the major classes of income and expense constituting pretax income from discontinued operations to the after-tax income from discontinued operations on the Consolidated Statements of Income were as follows:
202420232022
(In thousands)
Operating revenues$2,377,332 $3,589,251 $5,226,766 
Operating expenses2,241,162 3,422,393 4,853,408 
Operating (loss) income
136,170 166,858 373,358 
Other income (expense)12,446 10,599 4,119 
Interest expense7,118 47,229 38,590 
Income from discontinued operations before income taxes
141,498 130,228 338,887 
Income taxes41,463 45,638 88,650 
Discontinued operations, net of tax$100,035 $84,590 $250,237 
v3.25.0.1
Revenue from Contracts with Customers
 12 Months Ended
Dec. 31, 2024
Revenue from Contract with Customer [Abstract]  
Revenue from Contracts with Customers Revenue from Contracts with Customers
Revenue is recognized when a performance obligation is satisfied by transferring control over a product or service to a customer. Revenue is measured based on consideration specified in a contract with a customer and excludes any sales incentives and amounts collected on behalf of third parties. The Company is considered an agent for certain taxes collected from customers. As such, the Company presents revenues net of these taxes at the time of sale to be remitted to governmental authorities, including sales and use taxes.
As part of the adoption of ASC 606 - Revenue from Contracts with Customers, the Company elected the practical expedient to recognize the incremental costs of obtaining a contract as an expense when incurred if the amortization period of the asset that the Company otherwise would have recognized is 12 months or less.
Disaggregation
In the following table, revenue is disaggregated by the type of customer or service provided. The Company believes this level of disaggregation best depicts how the nature, amount, timing and uncertainty of revenue and cash flows are affected by economic factors. The table also includes a reconciliation of the disaggregated revenue by reportable segments. For more information on the Company's business segments, see Note 17.
Year ended December 31, 2024ElectricNatural gas distributionPipelineOtherTotal
(In thousands)
Residential utility sales
$140,054 $646,049 $— $— $786,103 
Commercial utility sales171,760 399,087 — — 570,847 
Industrial utility sales42,883 42,588 — — 85,471 
Other utility sales7,910 — — — 7,910 
Natural gas transportation— 60,645 174,623 — 235,268 
Natural gas storage— — 23,690 — 23,690 
Other59,288 40,703 13,139 195 113,325 
Intersegment eliminations(72)(130)(69,222)(195)(69,619)
Revenues from contracts with customers421,823 1,188,942 142,230 — 1,752,995 
Other revenues(7,417)12,033 367 — 4,983 
Total external operating revenues$414,406 $1,200,975 $142,597 $— $1,757,978 

Year ended December 31, 2023ElectricNatural gas distributionPipelineOtherTotal
(In thousands)
Residential utility sales$136,274 $724,600 $— $— $860,874 
Commercial utility sales170,321 442,507 — — 612,828 
Industrial utility sales43,063 45,205 — — 88,268 
Other utility sales7,270 — — — 7,270 
Natural gas transportation— 52,465 145,297 — 197,762 
Natural gas storage— — 18,254 — 18,254 
Other54,508 15,141 13,874 119 83,642 
Intersegment eliminations(138)(301)(62,533)(119)(63,091)
Revenues from contracts with customers411,298 1,279,617 114,892 — 1,805,807 
Other revenues(10,261)7,619 187 — (2,455)
Total external operating revenues$401,037 $1,287,236 $115,079 $— $1,803,352 
Year ended December 31, 2022ElectricNatural gas distributionPipelineOtherTotal
(In thousands)
Residential utility sales$138,634 $718,191 $— $— $856,825 
Commercial utility sales146,182 453,802 — — 599,984 
Industrial utility sales43,766 41,710 — — 85,476 
Other utility sales7,597 — — — 7,597 
Natural gas transportation— 48,886 129,290 — 178,176 
Natural gas storage— — 14,583 — 14,583 
Other45,608 13,617 11,450 86 70,761 
Intersegment eliminations(58)(216)(58,884)(86)(59,244)
Revenues from contracts with customers381,729 1,275,990 96,439 — 1,754,158 
Other revenues(4,714)(2,402)256 — (6,860)
Total external operating revenues$377,015 $1,273,588 $96,695 $— $1,747,298 
Remaining performance obligations
The remaining performance obligations at the pipeline segment include firm transportation and storage contracts with fixed pricing and fixed volumes. The Company has applied the practical expedient that does not require additional disclosures for contracts with an original duration of less than 12 months to certain firm transportation and non-regulated contracts. The Company's firm transportation and storage contracts included in the remaining performance obligations have weighted average remaining durations of less than five years and one year, respectively.
At December 31, 2024, the Company's remaining performance obligations were $606.5 million. The Company expects to recognize the following revenue amounts in future periods related to these remaining performance obligations: $82.1 million within the next 12 months or less; $81.5 million within the next 13 to 24 months; and $442.9 million in 25 months or more.
v3.25.0.1
Property, Plant and Equipment
 12 Months Ended
Dec. 31, 2024
Property, Plant and Equipment [Abstract]  
Property, Plant and Equipment Property, Plant and Equipment
Property, plant and equipment at December 31 was as follows:
20242023Weighted
Average
Depreciable
Life in Years
(Dollars in thousands, where applicable)
Electric:
Generation$1,014,906 $939,474 49
Distribution546,121 521,215 47
Transmission662,466 639,999 65
CWIP
81,316 115,103 0
Other176,007 153,248 15
Natural gas distribution:
Distribution2,955,435 2,771,540 53
Transmission146,710 115,057 56
Storage43,700 42,654 37
General229,034 215,572 13
CWIP
74,207 70,373 0
Other282,007 246,991 15
Pipeline:
Transmission1,173,259 1,035,995 46
Storage61,369 57,160 53
CWIP
29,629 57,038 0
Other73,749 68,194 17
Other:
Land and other
4,148 31,654 7
Less accumulated depreciation and amortization
2,209,771 2,076,375 
Net property, plant and equipment$5,344,292 $5,004,892 
v3.25.0.1
Regulatory Assets and Liabilities
 12 Months Ended
Dec. 31, 2024
Regulatory Assets and Liabilities Disclosure [Abstract]  
Regulatory Assets and Liabilities Regulatory Assets and Liabilities
The following table summarizes the individual components of unamortized regulatory assets and liabilities as of December 31:
Estimated Recovery or Refund Period*2024 2023 
(In thousands)
Regulatory assets:
Current:
Natural gas costs recoverable through rate adjustments
Up to 1 year
$91,091 $98,844 
Environmental compliance programs
Up to 1 year
76,964 5,525 
Conservation programs
Up to 1 year
19,123 14,425 
Electric fuel and purchased power deferral
Up to 1 year
9,662 33,918 
Decoupling mechanisms
Up to 1 year
6,767 — 
Cost recovery mechanisms
Up to 1 year
5,114 9,153 
Other
Up to 1 year
6,715 10,627 
215,436 172,492 
Noncurrent:
Pension and postretirement benefits**142,064 142,511 
Cost recovery mechanisms
Up to 24 years
76,542 85,944 
Plant costs/asset retirement obligationsOver plant lives47,042 46,009 
Manufactured gas plant site remediation-27,964 26,127 
Taxes recoverable from customersOver plant lives12,221 12,249 
Electric fuel and purchased power deferral
Up to 2 years
4,349 — 
Covid-19 deferred costs-4,167 2,746 
Long-term debt refinancing costs
Up to 36 years
2,011 2,600 
Environmental compliance programs-— 66,806 
Natural gas costs recoverable through rate adjustments
Up to 2 years
— 55,493 
Other
Up to 14 years
5,990 6,614 
322,350 447,099 
Total regulatory assets$537,786 $619,591 
Regulatory liabilities:
Current:
Environmental compliance
Up to 1 year
$72,387 $— 
Natural gas costs refundable through rate adjustments
Up to 1 year
45,427 43,161 
Margin sharing
Up to 1 year
4,156 5,243 
Provision for rate refund
Up to 1 year
3,677 6,866 
Taxes refundable to customers
Up to 1 year
2,163 2,149 
Conservation programs
Up to 1 year
2,082 2,130 
Cost recovery mechanisms
Up to 1 year
1,720 6,284 
Other
Up to 1 year
5,555 4,928 
137,167 70,761 
Noncurrent:
Plant removal and decommissioning costsOver plant lives217,603 220,147 
Taxes refundable to customersOver plant lives185,402 193,578 
Cost recovery mechanisms
Up to 17 years
30,354 21,791 
Accumulated deferred investment tax creditOver plant lives18,788 15,740 
Pension and postretirement benefits**4,862 6,044 
Environmental compliance programs-— 61,941 
Other
Up to 13 years
2,161 1,809 
459,170 521,050 
Total regulatory liabilities$596,337 $591,811 
Net regulatory position$(58,551)$27,780 
*Estimated recovery or refund period for amounts currently being recovered or refunded in rates to customers.
**    Recovered as expense is incurred or cash contributions are made.
As of December 31, 2024 and 2023, approximately $181.2 million and $194.3 million, respectively, of regulatory assets were not earning a rate of return but are expected to be recovered from customers in future rates. These assets are largely comprised of the unfunded portion of pension and postretirement benefits, asset retirement obligations, certain pipeline integrity costs and the estimated future cost of manufactured gas plant site remediation.
The Company is subject to environmental compliance regulations in certain states which require natural gas distribution companies to reduce overall GHG emissions to certain thresholds as established by each applicable state. Compliance with these standards may be achieved through increased energy efficiency and conservation measures, purchased emission allowances and offsets and purchases of low carbon fuels. Emission allowances are allocated by the respective states to the Company at no cost, of which a portion is required to be sold at auction. The compliance costs for these regulations and the revenues from the sale of the allocated emissions allowances are passed through to customers in rates and the Company has, accordingly, deferred the environmental compliance costs as a regulatory asset and proceeds from the sale of allowances as a regulatory liability.
For a discussion of the Company's most recent cases by jurisdiction, see Note 20.
If, for any reason, the Company's regulated businesses cease to meet the criteria for application of regulatory accounting for all or part of their operations, the regulatory assets and liabilities relating to those portions ceasing to meet such criteria would be written off and included in the statement of income or accumulated other comprehensive loss in the period in which the discontinuance of regulatory accounting occurs.
v3.25.0.1
Environmental Allowances and Obligations
 12 Months Ended
Dec. 31, 2024
Environmental Remediation Obligations [Abstract]  
Environmental Allowance and Obligations Environmental Allowances and Obligations
Beginning in 2023, the Company's natural gas distribution segment acquires environmental allowances as part of its requirement to comply with environmental regulations in certain states. Allowances are allocated by the respective states to the Company at no cost and additional allowances are required to be purchased as needed based on the requirements in the respective states. The segment records purchased and allocated environmental allowances at weighted average cost under the inventory method of accounting. Environmental allowances are included in Prepayments and other current assets and noncurrent assets - Other on the Consolidated Balance Sheets.
Environmental compliance obligations, which are based on GHG emissions, are measured at the carrying value of environmental allowances held plus the estimated value of additional allowances necessary to satisfy the compliance obligation. Environmental compliance obligations are included in current liabilities - Other accrued liabilities and noncurrent liabilities - Other on the Consolidated Balance Sheets.
The Company recognizes revenue from the sale of emissions allowances allocated under the environmental programs when the allowances are sold at auction. The revenues associated with the sale of these allowances are deferred as a component of the respective jurisdiction’s regulatory liability for environmental compliance.
As environmental allowances are surrendered, the segment reduces the associated environmental compliance assets and liabilities from the Consolidated Balance Sheets. The expenses and revenues associated with the Company’s environmental allowances and obligations are deferred as regulatory assets and liabilities and recognized as a component of purchased natural gas sold as recovered in customer rates. For more information on the Company’s regulatory assets and liabilities, see Note 6.
v3.25.0.1
Goodwill
 12 Months Ended
Dec. 31, 2024
Goodwill and Intangible Assets Disclosure [Abstract]  
Goodwill Goodwill
The carrying amount of goodwill at the natural gas distribution segment, which remained unchanged, was $345.7 million, respectively, at both December 31, 2024 and 2023. No impairments of goodwill have been recorded in these periods.
v3.25.0.1
Fair Value Measurements
 12 Months Ended
Dec. 31, 2024
Fair Value Disclosures [Abstract]  
Fair Value Measurements Fair Value Measurements
Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability (an exit price) in an orderly transaction between market participants at the measurement date. The fair value ASC establishes a hierarchy for grouping assets and liabilities, based on the significance of inputs. The estimated fair values of the Company's assets and liabilities measured on a recurring basis are determined using the market approach.
The Company measures its investments in certain fixed-income and equity securities at fair value with changes in fair value recognized in income. The Company anticipates using these investments, which consist of insurance contracts, to satisfy its obligations under its unfunded, nonqualified defined benefit and defined contribution plans for executive officers and certain key management employees and invests in these fixed-income and equity securities for the purpose of earning investment returns and capital appreciation. These investments, which totaled $59.3 million and $62.9 million at December 31, 2024 and 2023, respectively, are classified as investments on the Consolidated Balance Sheets. The net unrealized gain on these investments for the year ended December 31, 2024 and 2023, was $5.9 million and $7.4 million, respectively. The net unrealized loss on these investments for the year ended December 31, 2022 was $11.2 million. The change in fair value, which is considered part of the cost of the plan, is classified in Other income on the Consolidated Statements of Income. In the first quarter of 2024 and the fourth quarter of 2023, the Company withdrew $9.0 million and $20.0 million, respectively, of its cost basis, which reduced Investments on the Consolidated Balance Sheets.
The Company did not elect the fair value option, which records gains and losses in income, for its available-for-sale securities, which include mortgage-backed securities and U.S. Treasury securities. These available-for-sale securities are recorded at fair value and are classified as Investments on the Consolidated Balance Sheets. Unrealized gains or losses are recorded in Accumulated other comprehensive loss on the Consolidated Balance Sheets. Details of available-for-sale securities were as follows:
December 31, 2024CostGross
Unrealized
Gains		Gross
Unrealized
Losses		Fair Value
(In thousands)
Mortgage-backed securities$7,933 $4 $383 $7,554 
U.S. Treasury securities3,945 80 1 4,024 
Total$11,878 $84 $384 $11,578 
December 31, 2023CostGross
Unrealized
Gains		Gross
Unrealized
Losses		Fair Value
(In thousands)
Mortgage-backed securities$8,234 $17 $470 $7,781 
U.S. Treasury securities3,521 28 8 3,541 
Total$11,755 $45 $478 $11,322 
The Company's assets measured at fair value on a recurring basis were as follows:
 
Fair Value Measurements at December 31, 2024, Using
 
 Quoted Prices
in Active
Markets for
Identical
Assets
(Level 1)		Significant
Other
Observable
Inputs
(Level 2)		Significant
Unobservable
Inputs
 (Level 3)		Balance at December 31, 2024
 (In thousands)
Assets:    
Money market funds$— $12,879 $— $12,879 
Insurance contracts*— 59,282 — 59,282 
Available-for-sale securities:
Mortgage-backed securities— 7,554 — 7,554 
U.S. Treasury securities— 4,024 — 4,024 
Total assets measured at fair value$— $83,739 $— $83,739 
*The insurance contracts invest approximately 58 percent in fixed-income investments, 17 percent in common stock of large-cap companies, 8 percent in target date investments, 8 percent in common stock of mid-cap companies, 4 percent in common stock of small-cap companies, 4 percent in cash equivalents, and 1 percent in international investments.
 
Fair Value Measurements at December 31, 2023, Using
 
 Quoted Prices
in Active
Markets for
Identical
Assets
 (Level 1)		Significant
Other
Observable
Inputs
(Level 2)		Significant
Unobservable
Inputs
 (Level 3)		Balance at December 31, 2023
 (In thousands)
Assets:    
Money market funds$— $6,409 $— $6,409 
Insurance contracts*— 62,936 — 62,936 
Available-for-sale securities:
Mortgage-backed securities— 7,781 — 7,781 
U.S. Treasury securities— 3,541 — 3,541 
Total assets measured at fair value$— $80,667 $— $80,667 
*The insurance contracts invest approximately 60 percent in fixed-income investments, 15 percent in common stock of large-cap companies, 8 percent in target date investments, 7 percent in common stock of mid-cap companies, 5 percent in common stock of small-cap companies, 3 percent in cash equivalents, 1 percent in high yield investments, and 1 percent in international investments.
The Company's money market funds are valued at the net asset value of shares held at the end of the period, based on published market quotations on active markets, or using other known sources including pricing from outside sources. The estimated fair value of the Company's mortgage-backed securities and U.S. Treasury securities are based on comparable market transactions, other observable inputs or other sources, including pricing from outside sources. The estimated fair value of the Company's insurance contracts are based on contractual cash surrender values that are determined primarily by investments in managed separate accounts of the insurer. These amounts approximate fair value. The managed separate accounts are valued based on other observable inputs or corroborated market data.
Though the Company believes the methods used to estimate fair value are consistent with those used by other market participants, the use of other methods or assumptions could result in a different estimate of fair value.
The Company applies the provisions of the fair value measurement standard to its nonrecurring, non-financial measurements, including long-lived asset impairments. These assets are not measured at fair value on an ongoing basis but are subject to fair value adjustments only in certain circumstances. The Company reviews the carrying value of its long-lived assets, excluding goodwill, whenever events or changes in circumstances indicate that such carrying amounts may not be recoverable.
The Company's long-term debt is not measured at fair value on the Consolidated Balance Sheets and the fair value is being provided for disclosure purposes only. The fair value was categorized as Level 2 in the fair value hierarchy and was based on discounted future cash flows using current market interest rates. The estimated fair value of the Company's Level 2 long-term debt at December 31 was as follows:
 20242023
 (In thousands)
Carrying Amount$2,292,610 $2,166,223 
Fair Value$1,963,396 $1,914,039 
The carrying amounts of the Company's remaining financial instruments included in current assets and current liabilities approximate their fair values.
v3.25.0.1
Debt
 12 Months Ended
Dec. 31, 2024
Debt Disclosure [Abstract]  
Debt Debt
Due to the Knife River separation, Centennial repaid all of its outstanding debt in the second quarter of 2023, which was funded by the Knife River repayment and the Company entering into various new debt instruments. Refer to Note 3 for additional information related to the repayment of debt associated with the Knife River separation.

Certain debt instruments of the Company and its subsidiaries contain restrictive and financial covenants and cross-default provisions. In order to borrow under the respective debt agreements, the Company and its subsidiaries must be in compliance with the applicable covenants and certain other conditions, all of which the Company and its subsidiaries, as applicable, were in compliance with at December 31, 2024. In the event the Company or its subsidiaries do not comply with the applicable covenants and other conditions, alternative sources of funding may need to be pursued.
The following table summarizes the outstanding revolving credit facilities of the Company and its subsidiaries:
CompanyFacilityFacility
Limit		 
Amount Outstanding at December 31, 2024
Amount Outstanding at December 31, 2023
Letters of
Credit at December 31, 2024
Expiration
Date
  (In millions)
Montana-Dakota Utilities Co.Commercial paper/Revolving credit agreement (a)$200.0  $81.4 $144.2 $— 10/18/28
Cascade Natural Gas Corporation
Revolving credit agreement
$175.0 (b)$64.6 $15.4 $2.2 (c)6/20/29
Intermountain Gas Company
Revolving credit agreement
$175.0 
(b)
$105.1 $30.7 $— 6/20/29
MDU Resources Group, Inc.
Revolving credit agreement
$200.0 
(d)
$— $— $12.1 (c)5/31/28
(a)The commercial paper program is supported by a revolving credit agreement with various banks (provisions allow for increased borrowings, at the option of Montana-Dakota on stated conditions, up to a maximum of $250.0 million). At December 31, 2024 and 2023, there were no amounts outstanding under the revolving credit agreement.
(b)Certain provisions allow for increased borrowings, up to a maximum of $225.0 million.
(c)Outstanding letter(s) of credit reduce the amount available under the credit agreement.
(d)Certain provisions allow for increased borrowings, up to a maximum of $250.0 million.
Montana-Dakota's commercial paper program is supported by a revolving credit agreement. While the amount of commercial paper outstanding does not reduce available capacity under the revolving credit agreement, Montana-Dakota does not issue commercial paper in an aggregate amount exceeding the available capacity under the credit agreement. The commercial paper and revolving credit agreement borrowings may vary during the period, largely the result of fluctuations in working capital requirements due to the seasonality of certain operations of Montana-Dakota.
Short-term debt
Cascade On January 20, 2023, Cascade entered into a $150.0 million term loan agreement with a SOFR-based variable interest rate and a maturity date of January 19, 2024. On December 5, 2023, Cascade paid down $100.0 million of the outstanding balance. On January 19, 2024, Cascade made the final $50.0 million repayment on the term loan agreement.
Intermountain On January 20, 2023, Intermountain entered into a $125.0 million term loan agreement with a SOFR-based variable interest rate and a maturity date of January 19, 2024. In March, April and May 2023, Intermountain paid down $20.0 million, $30.0 million, and $30.0 million, respectively, of the outstanding balance. On January 19, 2024 Intermountain made the final $45.0 million repayment on the term loan agreement.

MDU Resources Group, Inc. On May 31, 2023, the Company entered into a $150.0 million revolving credit agreement with a SOFR-based variable interest rate and a maturity date of May 29, 2024. At December 31, 2023, the Company had no amount outstanding, which remained that way until this agreement matured and subsequently terminated in May 2024.
Long-term debt
Long-term Debt Outstanding Long-term debt outstanding was as follows:
 
Weighted Average Interest Rate at December 31, 2024
20242023
 (In thousands)
Senior notes due on dates ranging from August 23, 2025 to June 15, 2062
4.57 %$1,947,000 $1,882,000 
Credit agreements due on June 20, 2029
5.79 %169,700 46,100 
Commercial paper supported by revolving credit agreement
4.76 %81,400 144,200 
Term loan agreements due on dates ranging from September 3, 2032 to April 1, 2039
4.44 %65,600 64,300 
Medium-term notes due on dates ranging from September 15, 2027 to March 16, 2029
7.32 %35,000 35,000 
Other notes due on dates ranging from May 31, 2028 to November 30, 2038
6.00 %346 980 
Less unamortized debt issuance costs6,436 6,357 
Total long-term debt2,292,610 2,166,223 
Less current maturities161,700 61,319 
Net long-term debt$2,130,910 $2,104,904 
Montana-Dakota On October 18, 2023, Montana-Dakota amended and restated its revolving credit agreement to increase the borrowing capacity to $200.0 million and extend the maturity date to October 18, 2028. Montana-Dakota's revolving credit agreement supports its commercial paper program. Commercial paper borrowings under this agreement are classified as long-term debt as they are intended to be refinanced on a long-term basis through continued commercial paper borrowings. The credit agreement contains customary covenants and provisions, including covenants of Montana-Dakota not to permit, as of the end of any fiscal quarter, the ratio of funded debt to total capitalization (determined on a consolidated basis) to be greater than 65 percent. Other covenants include limitations on the sale of certain assets and on the making of certain loans and investments.
On July 11, 2024, Montana-Dakota issued $125.0 million of senior notes under a note purchase agreement with maturity dates ranging from July 11, 2039 to July 11, 2054, at a weighted average interest rate of 5.96 percent. The agreement contains customary covenants and provisions, including a covenant of Montana-Dakota not to permit, at any time, the ratio of total debt to capitalization to be greater than 65 percent. The covenants also include certain restrictions on the sale of certain assets, loans and investments.
Montana-Dakota's ratio of total debt to total capitalization at December 31, 2024, was 48 percent.
Cascade On June 20, 2024, Cascade amended and restated its revolving credit agreement to increase the borrowing capacity from $100.0 million to $175.0 million and extend the maturity date to June 20, 2029. Any borrowings under the revolving credit agreement are classified as long-term debt as they are intended to be refinanced on a long-term basis through continued borrowings. The credit agreement contains customary covenants and provisions, including a covenant of Cascade not to permit, at any time, the ratio of total debt to total capitalization to be greater than 65 percent. Other covenants include restrictions on the sale of certain assets, limitations on indebtedness and the making of certain investments.
Cascade's ratio of total debt to total capitalization at December 31, 2024, was 50 percent.
Intermountain On June 20, 2024, Intermountain amended and restated its revolving credit agreement to increase the borrowing capacity from $100.0 million to $175.0 million and extend the maturity date to June 20, 2029. Any borrowings under the revolving credit agreement are classified as long-term debt as they are intended to be refinanced on a long-term basis through continued borrowings. The credit agreement contains customary covenants and provisions, including a covenant of Intermountain not to permit, at any time, the ratio of total debt to total capitalization to be greater than 65 percent. Other covenants include restrictions on the sale of certain assets, limitations on indebtedness and the making of certain investments.
Intermountain's ratio of total debt to total capitalization at December 31, 2024, was 60 percent.
MDU Resources Group, Inc. On May 31, 2023, the Company entered into a $200.0 million revolving credit agreement with a SOFR-based variable interest rate and a maturity date of May 31, 2028. Any borrowings under the revolving credit agreement are classified as long-term debt as they are intended to be refinanced on a long-term basis through continued borrowings. The credit agreement contains customary covenants and provisions, including a covenant of the Company not to permit, at any time, the ratio of total debt to total capitalization to be greater than 65 percent. The covenants also include certain restrictions on the sale of certain assets, loans and investments.
On May 31, 2023, the Company entered into a $375.0 million term loan agreement with a SOFR-based variable interest rate and a maturity date of May 31, 2025. On November 15, 2023, the Company paid down $185.0 million of the term loan agreement. On November 1, 2024, the Company repaid its remaining outstanding balance of $190.0 million and the term loan agreement subsequently terminated. The Company's repayment was
funded by the Everus repayment of debt in connection with the separation. Refer to Note 3 for additional information related to the repayment of debt associated with the Everus separation.
The Company's ratio of total debt to total capitalization at December 31, 2024, was 46 percent.
WBI Energy Transmission WBI Energy Transmission has a $350.0 million uncommitted note purchase and private shelf agreement with an expiration date of December 22, 2025. WBI Energy Transmission had $235.0 million of notes outstanding at December 31, 2024, which reduced the remaining capacity under this uncommitted private shelf agreement to $115.0 million. This agreement contains customary covenants and provisions, including a covenant of WBI Energy Transmission not to permit, as of the end of any fiscal quarter, the ratio of total debt to total capitalization to be greater than 55 percent. Other covenants include a limitation on priority debt, restrictions on the sale of certain assets and the making of certain investments.
On April 1, 2024, WBI Energy Transmission entered into a $60.0 million term loan agreement with an interest rate of 4.52 percent and a maturity date of April 1, 2039, with the principal to be repaid in equal annual installments of $4.0 million each, beginning March 2025 and continuing through the maturity date. The agreement contains customary covenants and provisions, including a covenant of WBI Energy Transmission not to permit, at any time, the ratio of total debt to total capitalization to be greater than 65 percent. The covenants also include certain restrictions on the sale of certain assets, loans and investments.
WBI Energy Transmission's ratio of total debt to total capitalization at December 31, 2024, was 40 percent.
Schedule of Debt Maturities Long-term debt maturities, which excludes unamortized debt issuance costs and discount, for the five years and thereafter following December 31, 2024, were as follows:
20252026202720282029Thereafter
(In thousands)
Long-term debt maturities$161,700 $144,700 $24,700 $161,100 $244,400 $1,562,446 
v3.25.0.1
Asset Retirement Obligations
 12 Months Ended
Dec. 31, 2024
Asset Retirement Obligation [Abstract]  
Asset Retirement Obligations Asset Retirement Obligations
The Company records obligations related to retirement costs of natural gas distribution lines, natural gas transmission lines, natural gas storage wells, decommissioning of certain electric generating facilities, special handling and disposal of hazardous materials at certain electric generating facilities, natural gas distribution facilities and buildings, and certain other obligations as asset retirement obligations.
A reconciliation of the Company's liability, which the current portion is included in other accrued liabilities on the Consolidated Balance Sheets, for the years ended December 31 was as follows:
2024 2023 
(In thousands)
Balance at beginning of year$385,154 $373,147 
Liabilities incurred2,721 533 
Liabilities settled(5,271)(6,633)
Accretion expense*19,655 18,894 
Revisions in estimates4,388 (787)
Balance at end of year$406,647 $385,154 
*Includes $19.6 million and $18.9 million in 2024 and 2023, respectively, recorded to regulatory assets.
The 2024 revisions in estimates consist principally of updated asset retirement obligation costs resulting from decommissioning studies performed for electric generating facilities at the electric segment.
The Company believes that largely all expenses related to asset retirement obligations at the Company's regulated operations will be recovered in rates over time and, accordingly, defers such expenses as regulatory assets. For more information on the Company's regulatory assets and liabilities, see Note 6.
v3.25.0.1
Equity
 12 Months Ended
Dec. 31, 2024
Equity [Abstract]  
Equity Equity
The Company depends on earnings and dividends from its subsidiaries to pay dividends on common stock. The Company has paid quarterly dividends for 87 consecutive years. For the years ended December 31, 2024, 2023 and 2022, dividends declared on common stock were $.5100, $.6950 and $.8750 per common share, respectively. Dividends on common stock are paid quarterly to the stockholders as of the record date. For the years ended December 31, 2024, 2023 and 2022, the dividends declared to common stockholders were $103.9 million, $141.5 million and $177.9 million, respectively.
The declaration and payment of dividends of the Company is at the sole discretion of the board of directors. In addition, the Company's subsidiaries are generally restricted to paying dividends out of capital accounts or net assets. The following discusses the most restrictive limitations.
Certain credit agreements and regulatory limitations of the Company's subsidiaries also contain restrictions on dividend payments. The most restrictive limitation requires the Company's subsidiaries not to permit the ratio of funded debt to capitalization to be greater than 65 percent. Based on this limitation, approximately $1.3 billion of the net assets of the Company's subsidiaries, which represents common stockholders' equity including retained earnings, would be restricted from use for dividend payments at December 31, 2024.
The Company may sell any combination of common stock and debt securities if warranted by market conditions and the Company's capital requirements. Any public offer and sale of such securities will be made only by means of a prospectus meeting the requirements of the Securities Act and the rules and regulations thereunder.
The K-Plan provides participants the option to invest in the Company's common stock. For the years ended December 31, 2024, 2023 and 2022, the K-Plan purchased shares of common stock on the open market. At December 31, 2024, there were 7.2 million shares of common stock reserved for original issuance under the K-Plan.
The Company currently has 2.0 million shares of preferred stock authorized to be issued with a $100 par value. At December 31, 2024 and 2023, there were no shares outstanding.
v3.25.0.1
Stock-Based Compensation
 12 Months Ended
Dec. 31, 2024
Share-Based Payment Arrangement [Abstract]  
Stock-Based Compensation Stock-Based Compensation
The Company has stock-based compensation plans under which it is currently authorized to grant RSUs and other stock awards. As of December 31, 2024, there were 2.3 million remaining shares available to grant under these plans. The Company either purchases shares on the open market or issues new shares of common stock to satisfy the vesting of stock-based awards.
Separations of Knife River and Everus
In connection with the completed separations of Knife River and Everus through spinoffs, the provisions of the existing compensation plans required adjustments to the number and terms of outstanding employee time-vested RSUs and PSAs to preserve the intrinsic value of the awards immediately prior to each separation. The outstanding awards will continue to vest over the original vesting period, which is generally three years from the grant date. The outstanding PSAs in place at the time of the Knife River spinoff were modified to no longer be subject to performance-based vesting conditions. The number of PSAs were first adjusted for performance. The combined performance factors were determined based on the performance of the Company as of December 31, 2022. As a result, there were no outstanding PSAs at December 31, 2023. Outstanding awards at the time of the spinoffs were converted into awards of the holder’s employer following each separation. The Company incurred $1.7 million of incremental compensation expense related to the conversion of the RSUs associated with the Everus spinoff, of which $854,000 was recognized in 2024 and the remainder will be recognized in expense over the remaining service periods of the applicable awards.
Total stock-based compensation expense (after tax) was $7.1 million, $5.1 million and $6.9 million in 2024, 2023 and 2022, respectively. The Company uses the straight-line amortization method to recognize compensation expense related to RSUs, which only has a service condition. The Company recognized compensation expense related to PSAs with market-based performance metrics on a straight-line basis over the requisite service period. As of December 31, 2024, total remaining unrecognized compensation expense related to stock-based compensation was approximately $8.4 million (before income taxes) which will be amortized over a weighted average period of 1.3 years.
Stock awards
Non-employee directors receive shares of common stock in addition to and in lieu of cash payment for directors' fees. There were 46,341 shares with a fair value of $850,000, 50,717 shares with a fair value of $950,000 and 40,800 shares with a fair value of $1.2 million issued to non-employee directors during the years ended December 31, 2024, 2023 and 2022, respectively.
RSUs
In February 2024, 2023 and 2022, key employees were granted RSUs under the long-term performance-based incentive plan authorized by the Company's compensation committee. The compensation committee has the authority to select the recipients of awards, determine the type and size of awards, and establish certain terms and conditions of unit award grants. The shares vest over three years, contingent on continued employment. Compensation expense is recognized over the vesting period. Upon vesting, participants receive dividends that accumulate during the vesting period.

As previously discussed, adjustments were made to the number of RSUs to preserve the intrinsic value of the awards in connection with the spinoffs of Knife River and Everus and outstanding PSAs in place at the time of the Knife River spinoff were converted to RSUs.
Target grants of RSUs outstanding at December 31, 2024, were as follows:
Grant DatePerformance PeriodTarget Grant of Shares
February 2023/ July 20232023-2025542,233 
February 2024/ June 20242024-2026698,284 
A summary of the status of the RSUs for the year ended December 31, 2024, was as follows:
RSUs
 
Number of Shares
Weighted
Average
Grant-Date
Fair Value
**
Nonvested at beginning of period873,300 $21.16 
Granted pre-separation of Everus
478,938 20.89 
Forfeited
(112,826)21.35 
Non-vested pre-separation of Everus
1,239,412 
Adjustments related to the Everus separation*
663,661 
Vested shares
(662,556)12.04 
Nonvested at end of period1,240,517 $12.56 
*Includes the conversion adjustments to preserve the intrinsic value of the awards and the cancellation of outstanding awards held by employees that transferred to Everus, which were replaced with awards issued by Everus as part of the separation.
** Weighted average grant-date fair values post-separation of Everus reflects incremental fair value related to modifying the awards and the Company's adjusted stock price due to the separation.
Historical PSAs
In February 2022, key employees were granted PSAs under the long-term performance-based incentive plan authorized by the Company's compensation committee. The compensation committee has the authority to select the recipients of awards, determine the type and size of awards, and establish certain terms and conditions of award grants. Upon vesting, participants receive dividends that accumulate during the vesting period. Share awards were generally earned over a three-year vesting period and tied to financial metrics. However, in connection with the spinoff of Knife River, the outstanding PSAs were converted to RSUs. As a result, there were no outstanding PSAs at December 31, 2024.
Under the market condition for these PSAs, participants could earn from zero to 200 percent of the apportioned target grant of shares based on the Company's total stockholder return relative to that of the selected peer group. Compensation expense was based on the grant-date fair value as determined by Monte Carlo simulation. The blended volatility term structure ranges were comprised of 50 percent historical volatility and 50 percent implied volatility. Risk-free interest rates were based on U.S. Treasury security rates in effect as of the grant date. Assumptions used for initial grants applicable to the market condition for certain PSAs issued in 2022 were:
2022 
Weighted average grant-date fair value$36.25 
Blended volatility range
24.07% - 31.41%
Risk-free interest rate range
.71% - 1.68%
Weighted average discounted dividends per share$2.93 
Under the performance conditions for these PSAs, participants could earn from zero to 200 percent of the apportioned target grant of shares. The performance conditions were based on the Company's compound annual growth rate in earnings from continuing operations. The weighted average grant-date fair value per share for the PSAs applicable to these performance conditions issued in 2022 was $27.73.
The fair value of the PSAs that vested during the year ended December 31, 2022, was $7.6 million.
v3.25.0.1
Accumulated Other Comprehensive Loss
 12 Months Ended
Dec. 31, 2024
Equity [Abstract]  
Accumulated Other Comprehensive Loss Accumulated Other Comprehensive Loss
The Company's accumulated other comprehensive loss is comprised of losses on derivative instruments qualifying as hedges, postretirement liability adjustments and gain (loss) on available-for-sale investments.
The after-tax changes in the components of accumulated other comprehensive loss were as follows:
 Net
Unrealized
Loss on
Derivative
 Instruments
 Qualifying
as Hedges		Post-
retirement
 Liability
Adjustment		Net
Unrealized
Gain (Loss) on
Available-
for-sale
Investments		Total
Accumulated
 Other
Comprehensive
 Loss
 (In thousands)
At December 31, 2022$(125)$(29,900)$(558)$(30,583)
Other comprehensive income (loss) before reclassifications— (646)173 (473)
Amounts reclassified from accumulated other comprehensive loss81 242 43 366 
Net current-period other comprehensive income (loss)81 (404)216 (107)
Amounts reclassified related to the separation of Knife River44 12,262 — 12,306 
At December 31, 2023— (18,042)(342)(18,384)
Other comprehensive income before reclassifications
— 1,049 85 1,134 
Amounts reclassified from accumulated other comprehensive loss— 432 20 452 
Net current-period other comprehensive income
— 1,481 105 1,586 
At December 31, 2024$— $(16,561)$(237)$(16,798)
The following amounts were reclassified out of accumulated other comprehensive loss into net income. The amounts presented in parentheses indicate a decrease to net income on the Consolidated Statements of Income. The reclassifications for the years ended December 31 were as follows:
 20242023Location on Consolidated
Statements of Income
(In thousands)
Reclassification adjustment for loss on derivative instruments included in net income$— $(96)Interest expense
— 15 Income taxes
— (81)
Amortization of postretirement liability losses included in net periodic benefit credit(577)(320)Other income
145 78 Income taxes
(432)(242)
Reclassification adjustment on available-for-sale investments included in net income(25)(54)Other income
5 11 Income taxes
(20)(43)
Total reclassifications$(452)$(366)
v3.25.0.1
Income Taxes
 12 Months Ended
Dec. 31, 2024
Income Tax Disclosure [Abstract]  
Income Taxes Income Taxes
The components of income before income taxes from continuing operations for each of the years ended December 31 were as follows:
202420232022
(In thousands)
United States$198,662 $340,330 $123,447 
Income before income taxes from continuing operations$198,662 $340,330 $123,447 
Income tax expense (benefit) from continuing operations for the years ended December 31 was as follows:
 2024 2023 2022 
 (In thousands)
Current:   
Federal$30,412 $8,271 $(15,849)
State3,255 3,251 1,857 
 33,667 11,522 (13,992)
Deferred:
Income taxes:
Federal(17,321)(3,331)15,038 
State(1,805)(125)4,251 
Investment tax credit - net3,048 2,147 898 
 (16,078)(1,309)20,187 
Total income tax expense$17,589 $10,213 $6,195 
Components of deferred tax assets and deferred tax liabilities at December 31 were as follows:
 20242023
 (In thousands)
Deferred tax assets:  
Environmental compliance$33,730 $28,873 
Pension and postretirement25,508 27,584 
Compensation-related15,651 17,106 
Customer advances9,719 8,312 
Cost recovery mechanisms7,402 5,314 
Legal and environmental contingencies5,317 4,881 
Other20,386 13,045 
Total deferred tax assets117,713 105,115 
Deferred tax liabilities:  
Basis differences on property, plant and equipment426,493 404,039 
Pension and postretirement48,355 39,110 
Purchased gas adjustment20,441 34,618 
Environmental compliance17,260 16,221 
Cost recovery mechanisms19,245 22,604 
Legal and environmental contingencies6,300 5,902 
Other19,931 33,947 
Total deferred tax liabilities558,025 556,441 
Valuation allowance1,008 1,010 
Net deferred income tax liability$441,320 $452,336 
As of both December 31, 2024 and 2023, the Company had various state income tax net operating loss carryforwards of $1.0 million and state income tax credit carryforwards, excluding alternative minimum tax credit carryforwards, of $31.6 million and $33.7 million, respectively. The state income tax credit carryforwards are due to expire between 2026 and 2038. Changes in tax regulations or assumptions regarding current and future taxable income could require additional valuation allowances in the future.
The following table reconciles the change in the net deferred income tax liability from December 31, 2023, to December 31, 2024, to deferred income tax expense:
 2024
(In thousands)
Change in net deferred income tax liability from the preceding table$(11,016)
Excess deferred income tax amortization(8,121)
Deferred taxes associated with other comprehensive income
(532)
Other3,591 
Deferred income tax expense for the period$(16,078)
Total income tax expense differs from the amount computed by applying the statutory federal income tax rate to income before taxes. The reasons for this difference were as follows:
Years ended December 31,202420232022
 Amount%Amount%Amount%
 (Dollars in thousands)
Computed tax at federal statutory rate$41,719 21.0 $71,469 21.0 $25,924 21.0 
Increases (reductions) resulting from:  
State income taxes, net of federal income tax
4,047 2.0 3,605 1.1 2,484 2.0 
State investment tax credit, net of federal income tax2,400 1.2 1,545 .5 1,624 1.3 
Executive compensation2,111 1.1 564 .2 683 .6 
Federal renewable energy credit
(16,871)(8.5)(15,175)(4.5)(15,343)(12.4)
Excess deferred income tax amortization(8,121)(4.1)(8,383)(2.5)(9,008)(7.3)
State tax rate change(2,317)(1.2)(9)— (3)— 
Research and development tax credit(1,465)(.7)(1,985)(.6)(1,692)(1.4)
Nonqualified benefit plans(1,142)(.6)(1,313)(.4)1,516 1.2 
Tax-free debt for equity exchange — — (38,967)(11.4)— — 
Other(2,772)(1.4)(1,138)(.3)10 — 
Total income tax expense$17,589 8.8 $10,213 3.1 $6,195 5.0 
The Company's effective tax rate for 2024 differs from the U.S. federal statutory rate of 21 percent due primarily to the impact of credits and deductions provided by law and excess deferred income tax amortization.
The Company and its subsidiaries file income tax returns in the U.S. federal jurisdiction, and various state and local jurisdictions. The Company is no longer subject to U.S. federal, non-U.S., state or local income tax examinations by tax authorities for years ending prior to 2020.
Total reserves for uncertain tax positions were not material. The Company recognizes interest and penalties accrued relative to unrecognized tax benefits in income tax expense.
v3.25.0.1
Cash Flow Information
 12 Months Ended
Dec. 31, 2024
Supplemental Cash Flow Information [Abstract]  
Cash Flow Information Cash Flow Information
Cash expenditures for interest and income taxes for the years ended December 31 were as follows:
202420232022
 (In thousands)
Interest, net*
$108,242 $112,839 $49,036 
Income taxes paid (refunded), net**
$43,572 $12,162 $(27,884)
*    AFUDC - borrowed was $11.0 million, $10.0 million and $2.2 million for the years ended December 31, 2024, 2023 and 2022, respectively.
**Income taxes paid, including discontinued operations, were $80.9 million, $62.5 million and $26.4 million for the years ended December 31, 2024, 2023 and 2022, respectively.
Noncash investing and financing transactions at December 31 were as follows:
202420232022
 (In thousands)
Property, plant and equipment additions in accounts payable$36,820 $46,364 $34,886 
Right-of-use assets obtained in exchange for new operating lease liabilities$1,787 $2,265 $1,324 
Debt for equity exchange of retained shares in Knife River
$— $293,239 $— 
v3.25.0.1
Business Segment Data
 12 Months Ended
Dec. 31, 2024
Segment Reporting [Abstract]  
Business Segment Data Business Segment Data
The Company's reportable segments are those that are based on the Company's method of internal reporting, which generally segregates the strategic business activities due to differences in products, services and regulation. The internal reporting of these operating segments is defined based on the reporting and review process used by the Company's CODM, the chief executive officer. The Company's operations are located within the United States.
The Company’s CODM regularly reviews discrete financial information of each reportable segment and uses net income to assess performance of each reportable segment. The CODM uses this information to assess performance and make decisions about resources to be allocated to each reportable segment, including capital and personnel. The information provided to the CODM is prepared at the reportable segment level in quarterly financial packages and on a more summarized basis monthly. Budget and forecast information is also provided to the CODM at the reportable segment level.
The electric segment generates, transmits and distributes electricity in Montana, North Dakota, South Dakota and Wyoming. The natural gas distribution segment distributes natural gas in those states, as well as in Idaho, Minnesota, Oregon and Washington. These operations also supply related value-added services.
The pipeline segment provides natural gas transportation and underground storage services through a FERC regulated pipeline system primarily in the Rocky Mountain and northern Great Plains regions of the United States. This segment also provides non-regulated energy-related services, including cathodic protection.
The Other category includes the activities of Centennial Capital, which, through its subsidiary InterSource Insurance Company, insures various types of risks as a captive insurer for certain of the Company's subsidiaries. The function of the captive insurer is to fund the self-insured layers of the insured Company's general liability, automobile liability, pollution liability and other coverages. Centennial Capital also owns certain personal property. In addition, the Other category includes certain assets, liabilities and tax adjustments of the holding company primarily associated with corporate functions, as well as the gain on the tax-free exchange of the retained shares in Knife River and costs associated with certain strategic initiatives. Also included are certain general and administrative costs (reflected in operation and maintenance expense) and interest expense, which were previously allocated to Knife River, Everus, Fidelity and the refining business and did not meet the criteria for discontinued operations.
Discontinued operations includes the results of operations for Knife River and Everus and certain associated separation costs, including interest on certain debt facilities repaid in connection with the separations. For the comparative periods below, Everus' operations are only reflected through October 2024 compared to the full year in 2023 and 2022 and Knife River's operations are only reflected through May 2023, compared to the full year in 2022. Discontinued operations also includes the supporting activities of Fidelity other than certain general and administrative costs and interest expense as described above.
The information below follows the same accounting policies as described in Note 2. Information on the Company's segments as of December 31 and for the years then ended was as follows:
Year ended December 31, 2024ElectricNatural gas distributionPipelineOtherConsolidated
(In thousands)
Operating revenues:
External operating revenues$414,406 $1,200,975 $142,597 $— $1,757,978 
Intersegment operating revenues72 130 69,222 195 69,619 
Operation and maintenance:
External operation and maintenance94,897 231,087 75,456 13,051 414,491 
Intersegment operation and maintenance72 130 324 195 721 
Purchased natural gas sold:
External purchased natural gas sold— 630,403 — — 630,403 
Intersegment purchased natural gas sold— 68,898 — — 68,898 
Electric fuel and purchased power
141,148 — — — 141,148 
Depreciation and amortization66,524 101,958 29,362 2,234 200,078 
Taxes, other than income17,605 76,042 12,175 394 106,216 
Other income:
External other income
8,205 25,509 5,850 1,803 41,367 
Intersegment other income
— — 655 14,798 15,453 
Interest expense:
External interest expense30,058 63,185 10,862 4,242 108,347 
Intersegment interest expense— — 4,633 10,820 15,453 
Income tax expense (benefit)
(2,414)7,974 17,470 (5,441)17,589 
Income (loss) from continuing operations
74,793 46,937 68,042 (8,699)181,073 
Discontinued operations, net of tax— — — 100,035 100,035 
Net income$74,793 $46,937 $68,042 $91,336 $281,108 
Capital expenditures (a)
$110,812 $286,152 $126,806 $1,728 $525,498 
Assets$1,976,912 
(b)
$3,730,532 (b)$1,151,317 $180,057 
(c)
$7,038,818 
Property, plant and equipment$2,480,816 (b)$3,731,093 (b)$1,338,006 $4,148 $7,554,063 
Accumulated depreciation and amortization
$716,736 
(b)
$1,139,223 
(b)
$351,045 $2,767 $2,209,771 
(a)Capital expenditures include noncash transactions such as capital expenditure-related accounts payable and AFUDC totaling $7.1 million.
(b)Includes allocations of common utility property for the Electric and Natural gas distribution segments.
(c)Other includes assets not directly assignable to a business (i.e. cash, cash equivalents and restricted cash, certain accounts receivable, certain investments and other miscellaneous current and deferred assets).
Year ended December 31, 2023ElectricNatural gas distributionPipelineOtherConsolidated
(In thousands)
Operating revenues:
External operating revenues$401,037 $1,287,236 $115,079 $— $1,803,352 
Intersegment operating revenues138 301 62,533 119 63,091 
Operation and maintenance:
External operation and maintenance92,521 219,481 70,386 24,693 407,081 
Intersegment operation and maintenance138 301 431 119 989 
Purchased natural gas sold:
External purchased natural gas sold— 742,965 — — 742,965 
Intersegment purchased natural gas sold— 62,102 — — 62,102 
Electric fuel and purchased power
134,779 — — — 134,779 
Depreciation and amortization64,253 95,300 26,811 4,086 190,450 
Taxes, other than income16,695 75,207 10,822 409 103,133 
Realized gain on tax-free exchange of the retained shares in Knife River— — — 186,556 186,556 
Other income:
External other income5,815 20,867 3,675 3,097 33,454 
Intersegment other income— — 217 13,431 13,648 
Interest expense:
External interest expense28,064 57,601 9,428 9,531 104,624 
Intersegment interest expense— — 3,842 9,806 13,648 
Income tax expense (benefit)
(1,019)6,927 12,409 (8,104)10,213 
Income from continuing operations
71,559 48,520 47,375 162,663 330,117 
Discontinued operations, net of tax— — (457)85,047 84,590 
Net income$71,559 $48,520 $46,918 $247,710 $414,707 
Capital expenditures (a)
$109,805 $274,836 $115,903 $(2,825)$497,719 
Assets$1,955,644 
(b)
$3,532,142 
(b)
$1,045,704 $1,299,669 
(c)
$7,833,159 
Property, plant and equipment
$2,369,039 
(b)
$3,462,187 
(b)
$1,218,387 $31,654 $7,081,267 
Accumulated depreciation and amortization
$660,438 
(b)
$1,068,037 
(b)
$328,010 $19,890 $2,076,375 
(a)Capital expenditures include noncash transactions such as capital expenditure-related accounts payable and AFUDC totaling $(13.6) million.
(b)Includes allocations of common utility property for the Electric and Natural gas distribution segments.
(c)Other includes assets of discontinued operations and assets not directly assignable to a business (i.e. cash, cash equivalents and restricted cash, certain accounts receivable, certain investments and other miscellaneous current and deferred assets).
Year ended December 31, 2022ElectricNatural gas distributionPipelineOtherConsolidated
(In thousands)
Operating revenues:
External operating revenues$377,015 $1,273,588 $96,695 $— $1,747,298 
Intersegment operating revenues58 216 58,884 86 59,244 
Operation and maintenance:
External operation and maintenance93,236 205,009 60,300 21,406 379,951 
Intersegment operation and maintenance58 216 638 86 998 
Purchased natural gas sold:
External purchased natural gas sold— 757,883 — — 757,883 
Intersegment purchased natural gas sold— 58,246 — — 58,246 
Electric fuel and purchased power
119,405 — — — 119,405 
Depreciation and amortization67,802 89,466 26,857 4,435 188,560 
Taxes, other than income16,917 71,095 12,318 299 100,629 
Other income:
External other income528 3,213 1,272 (1,753)3,260 
Intersegment other income— — 80 556 636 
Interest expense:
External interest expense28,526 42,126 9,966 65 80,683 
Intersegment interest expense— — 136 500 636 
Income tax expense (benefit)
(5,420)7,805 10,522 (6,712)6,195 
Income (loss) from continuing operations
57,077 45,171 36,194 (21,190)117,252 
Discontinued operations, net of tax— — (906)251,143 250,237 
Net income$57,077 $45,171 $35,288 $229,953 $367,489 
Capital expenditures (a)
$133,970 $240,064 $61,923 $2,272 $438,229 
Assets$1,856,258 
(b)
$3,214,452 
(b)
$961,893 $3,628,178 
(c)
$9,660,781 
Property, plant and equipment
$2,276,613 
(b)
$3,208,059 
(b)
$1,108,141 $36,705 $6,629,518 
Accumulated depreciation and amortization
$625,813 
(b)
$1,009,788 
(b)
$308,516 $19,143 $1,963,260 
(a)Capital expenditures include noncash transactions such as capital expenditure-related accounts payable and AFUDC totaling $4.4 million.
(b)Includes allocations of common utility property for the Electric and Natural gas distribution segments.
(c)Other includes assets of discontinued operations and assets not directly assignable to a business (i.e. cash, cash equivalents and restricted cash, certain accounts receivable, certain investments and other miscellaneous current and deferred assets).
A reconciliation of reportable segment operating revenues and assets to consolidated operating revenues and assets is as follows:
20242023 2022 
(In thousands)
Operating revenues reconciliation:
Total reportable segment operating revenues$1,827,402 $1,866,324 $1,806,456 
Other revenue195 119 86 
Elimination of intersegment operating revenues(69,619)(63,091)(59,244)
Total consolidated operating revenues$1,757,978 $1,803,352 $1,747,298 
Asset reconciliation:
Total reportable segment assets$6,892,959 $6,564,962 $6,061,151 
Other assets525,258 1,847,432 4,784,142 
Elimination of intersegment receivables(379,399)(579,235)(1,184,512)
Total consolidated assets$7,038,818 $7,833,159 $9,660,781 
v3.25.0.1
Employee Benefit Plans
 12 Months Ended
Dec. 31, 2024
Retirement Benefits [Abstract]  
Employee Benefit Plans Employee Benefit Plans
Pension and other postretirement benefit plans
The Company has noncontributory qualified defined benefit pension plans and other postretirement benefit plans for certain eligible employees. The Company uses a measurement date of December 31 for all of its pension and postretirement benefit plans.
Prior to 2013, defined benefit pension plan benefits and accruals for all nonunion and certain union plans were frozen and on June 30, 2015, the remaining union plan was frozen. These employees were eligible to receive additional defined contribution plan benefits.
Effective January 1, 2010, eligibility to receive retiree medical benefits was modified at certain of the Company's businesses. Employees who had attained age 55 with 10 years of continuous service by December 31, 2010, were provided the option to choose between a pre-65 comprehensive medical plan coupled with a Medicare supplement or a specified company funded Retiree Reimbursement Account, regardless of when they retire. All other eligible employees must meet the new eligibility criteria of age 60 and 10 years of continuous service at the time they retire to be eligible for a specified company funded Retiree Reimbursement Account. Employees hired after December 31, 2009, will not be eligible for retiree medical benefits.
In 2012, the Company modified health care coverage for certain retirees. Effective January 1, 2013, post-65 coverage was replaced by a fixed-dollar subsidy for retirees and spouses to be used to purchase individual insurance through a healthcare exchange.

In connection with the previously discussed separation of Knife River on May 31, 2023, Knife River's pension plan, including the associated assets and liabilities, was transferred to Knife River and therefore is no longer reflected as part of the Company. Also in connection with the separation, a remeasurement of the Company's postretirement plan and the Company's unfunded, non-qualified defined benefit plan were performed and the applicable liabilities from the plans relating to transferring employees were transferred to Knife River.
Changes in benefit obligation and plan assets and amounts recognized in the Consolidated Balance Sheets at December 31 were as follows:
 Pension BenefitsOther
Postretirement Benefits
 2024202320242023
Change in benefit obligation:(In thousands)
Benefit obligation at beginning of year$275,586 $278,286 $39,590 $40,315 
Service cost— — 505 534 
Interest cost12,799 13,521 1,837 1,956 
Plan participants' contributions— — 412 479 
Actuarial (gain) loss
(11,040)5,395 (3,420)(215)
Benefits paid(21,995)(21,616)(3,249)(3,479)
Benefit obligation at end of year255,350 275,586 35,675 39,590 
Change in net plan assets:    
Fair value of plan assets at beginning of year248,558 242,031 79,234 76,640 
Actual return on plan assets1,152 20,576 2,297 5,518 
Employer contribution2,911 7,567 71 76 
Plan participants' contributions— — 412 479 
Benefits paid(21,995)(21,616)(3,249)(3,479)
Fair value of net plan assets at end of year230,626 248,558 78,765 79,234 
Funded status - (under) over$(24,724)$(27,028)$43,090 $39,644 
Amounts recognized in the Consolidated Balance Sheets at December 31:    
Noncurrent assets - other$— $— $43,090 $39,644 
Noncurrent liabilities - other24,724 27,028 — — 
Benefit obligation (liabilities) assets - net amount recognized$(24,724)$(27,028)$43,090 $39,644 
Amounts recognized in accumulated other comprehensive loss:    
Actuarial loss (gain)$13,228 $32,273 $(809)$(3,515)
Prior service credit— — (37)(115)
Total$13,228 $32,273 $(846)$(3,630)
Amounts recognized in regulatory assets or liabilities:    
Actuarial loss (gain)$139,962 $140,232 $(1,478)$(1,146)
Prior service credit— — (1,303)(2,619)
Total$139,962 $140,232 $(2,781)$(3,765)
Employer contributions and benefits paid in the preceding table include only those amounts contributed directly to, or paid directly from, plan assets. Amounts related to regulated operations are recorded as regulatory assets or liabilities and are expected to be reflected in rates charged to customers over time. For more information on regulatory assets and liabilities, see Note 6.
In 2024, the actuarial gain recognized in the benefit obligation was primarily the result of an increase in the discount rate. In 2023, the actuarial loss recognized in the benefit obligation was primarily the result of a decrease in the discount rate. For more information on the discount rates, see the table below. Unrecognized pension actuarial gains and losses in excess of 10 percent of the greater of the projected benefit obligation or the market-related value of assets are amortized over the average life expectancy of plan participants for frozen plans. The market-related value of assets is determined using a five-year average of assets.
The pension plans all have accumulated benefit obligations in excess of plan assets. The projected benefit obligation, accumulated benefit obligation and fair value of plan assets for these plans at December 31 were as follows:
 2024 2023 
 (In thousands)
Projected benefit obligation$255,350 $275,586 
Accumulated benefit obligation$255,350 $275,586 
Fair value of plan assets$230,626 $248,558 
The components of net periodic benefit cost (credit), other than the service cost component, are included in other income on the Consolidated Statements of Income. Prior service credit is amortized on a straight-line basis over the average remaining service period of active participants. These components related to the Company's pension and other postretirement benefit plans for the years ended December 31 were as follows:
 Pension BenefitsOther
Postretirement Benefits
 202420232022202420232022
Components of net periodic benefit cost (credit):
(In thousands)
Service cost$— $— $— $505 $534 $894 
Interest cost12,799 13,521 9,396 1,837 1,956 1,383 
Expected return on assets(16,113)(17,194)(17,482)(5,315)(5,361)(5,277)
Amortization of prior service credit— — — (1,318)(1,318)(1,318)
Recognized net actuarial loss (gain)4,149 3,093 5,826 (288)(504)(570)
Net periodic benefit cost (credit), including amount capitalized
835 (580)(2,260)(4,579)(4,693)(4,888)
Less amount capitalized— — — — 107 175 
Net periodic benefit cost (credit)
835 (580)(2,260)(4,579)(4,800)(5,063)
Other changes in plan assets and benefit obligations recognized in accumulated comprehensive loss:    
Net loss (gain)
401 187 2,369 71 (604)(4,141)
Amortization of actuarial (loss) gain(359)(292)(1,310)130 108 (281)
Amortization of prior service credit— — — 45 78 125 
Reclassification of postretirement liability adjustment from regulatory asset— — 5,343 — — (992)
Total recognized in accumulated other comprehensive loss42 (105)6,402 246 (418)(5,289)
Other changes in plan assets and benefit obligations recognized in regulatory assets or liabilities:    
Net loss (gain)
3,520 1,826 9,757 (472)(107)11,920 
Amortization of actuarial (loss) gain(3,790)(2,801)(5,373)158 304 500 
Amortization of prior service credit— — — 1,273 1,273 1,273 
Reclassification of postretirement liability adjustment from regulatory asset— — (5,343)— — 992 
Total recognized in regulatory assets or liabilities(270)(975)(959)959 1,470 14,685 
Total recognized in net periodic benefit credit, accumulated other comprehensive loss and regulatory assets or liabilities$607 $(1,660)$3,183 $(3,374)$(3,748)$4,333 
Weighted average assumptions used to determine benefit obligations at December 31 were as follows:
 Pension BenefitsOther
Postretirement Benefits
 2024 2023 2024 2023 
Discount rate5.41 %4.84 %5.43 %4.85 %
Expected return on plan assets6.50 %6.50 %6.00 %6.00 %
Weighted average assumptions used to determine net periodic benefit cost (credit) for the years ended December 31 were as follows:
 Pension BenefitsOther
Postretirement Benefits
 2024202320242023
Discount rate4.84 %5.06 %4.85 %5.07 %
Expected return on plan assets6.50 %6.50 %6.00 %6.00 %
The expected rate of return on pension plan assets is based on a targeted asset allocation range determined by the funded ratio of the plan. As of December 31, 2024, the expected rate of return on pension plan assets is based on the targeted asset allocation range of 40 percent to 50 percent equity securities and 50 percent to 60 percent fixed-income securities and the expected rate of return from these asset categories. The expected rate of return on other postretirement plan assets is based on the targeted asset allocation range of 10 percent to 20 percent equity securities and 80 percent to 90 percent fixed-income securities and the expected rate of return from these asset categories. The expected return on plan assets for other postretirement benefits reflects insurance-related investment costs.
Health care rate assumptions for the Company's other postretirement benefit plans as of December 31 were as follows:
 2024 2023 
Health care trend rate assumed for next year (pre-65/post-65)
8.5%/6.25%
7.5%/6.5%
Health care cost trend rate - ultimate4.5 %4.5 %
Year in which ultimate trend rate achieved (pre-65/post-65)
2035/20342034/2033
The Company's other postretirement benefit plans include health care and life insurance benefits for certain retirees. The plans underlying these benefits may require contributions by the retiree depending on such retiree's age and years of service at retirement or the date of retirement. The Company contributes a flat dollar amount to the monthly premiums which is updated annually on January 1.
The Company expects to contribute to its defined benefit pension plans in 2025 the minimum funding requirement of $1.7 million. The Company expects to contribute approximately $18,000 to its postretirement benefit plans in 2025.
The following benefit payments, which reflect future service, as appropriate, and expected Medicare Part D subsidies at December 31, 2024, are as follows:
YearsPension
Benefits		Other
Postretirement Benefits		Expected
Medicare
Part D Subsidy
 (In thousands)
2025$22,280 $3,333 $48 
2026$22,070 $3,235 $43 
2027$21,870 $3,153 $37 
2028$21,500 $3,064 $32 
2029$21,170 $2,941 $27 
2030-2034$98,020 $13,659 $85 
Outside investment managers manage the Company's pension and postretirement assets. The Company's investment policy with respect to pension and other postretirement assets is to make investments solely in the interest of the participants and beneficiaries of the plans and for the exclusive purpose of providing benefits accrued and defraying the reasonable expenses of administration. The Company strives to maintain investment diversification to assist in minimizing the risk of large losses. The Company's policy guidelines allow for investment of funds in cash equivalents, fixed-income securities and equity securities. The guidelines prohibit investment in commodities and futures contracts, equity private placement, employer securities, leveraged or derivative securities, options, direct real estate investments, precious metals, venture capital and limited partnerships. The guidelines also prohibit short selling and margin transactions. The Company's practice is to periodically review and rebalance asset categories based on its targeted asset allocation percentage policy.
Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability (an exit price) in an orderly transaction between market participants at the measurement date. The fair value ASC establishes a hierarchy for grouping assets and liabilities, based on the significance of inputs. The estimated fair values of the Company's pension plans' assets are determined using the market approach.
The carrying value of the pension plans' Level 2 cash equivalents approximates fair value and is determined using observable inputs in active markets or the net asset value of shares held at year end, which is determined using other observable inputs including pricing from outside sources.
The estimated fair value of the pension plans' Level 1 and Level 2 equity securities are based on the closing price reported on the active market on which the individual securities are traded or other known sources including pricing from outside sources. The estimated fair value of the pension plans' Level 1 and Level 2 collective and mutual funds are based on the net asset value of shares held at year end, based on either published market quotations on active markets or other known sources including pricing from outside sources. The estimated fair value of the pension plans' Level 2 corporate and municipal bonds is determined using other observable inputs, including benchmark yields, reported trades, broker/dealer quotes, bids, offers, future cash flows and other reference data. The estimated fair value of the pension plans' Level 1 U.S. Government securities are valued based on quoted prices on an active market. The estimated fair value of the pension plans' Level 2 U.S. Government securities are valued mainly using other observable inputs, including benchmark yields, reported trades, broker/dealer quotes, bids, offers, to be announced prices, future cash flows and other reference data. The estimated fair value of the pension plans' Level 2 pooled separate accounts are determined using observable inputs in active markets or the net asset value of shares held at year end, or other observable inputs. Some of these securities are valued using pricing from outside sources.
All investments measured at net asset value in the tables that follow are invested in commingled funds, separate accounts or common collective trusts which do not have publicly quoted prices. The fair value of the commingled funds, separate accounts and common collective trusts are determined based on the net asset value of the underlying investments. The fair value of the underlying investments held by the commingled funds, separate accounts and common collective trusts is generally based on quoted prices in active markets.
Though the Company believes the methods used to estimate fair value are consistent with those used by other market participants, the use of other methods or assumptions could result in a different estimate of fair value.
The fair value of the Company's pension plans' assets (excluding cash) by class were as follows:
 
Fair Value Measurements
 at December 31, 2024, Using
 
 Quoted Prices
in Active
Markets for
Identical
Assets
 (Level 1)		Significant
Other
Observable
Inputs
 (Level 2)		Significant
Unobservable
 Inputs
 (Level 3)		Balance at December 31, 2024
 (In thousands)
Assets:    
Cash equivalents$— $4,512 $— $4,512 
Equity securities: 
U.S. companies(2)— — (2)
Collective and mutual funds (a)72,777 93,606 — 166,383 
U.S. Government securities33,616 25,857 — 59,473 
Investments measured at net asset value (b)— — — 260 
Total assets measured at fair value$106,391 $123,975 $— $230,626 
(a)Collective and mutual funds invest approximately 39 percent in corporate bonds, 19 percent in U.S. Government securities, 17 percent in other investments, 15 percent in common stock of international companies, 9 percent in common stock of large-cap and mid-cap U.S. companies, and 1 percent cash and cash equivalents.
(b)In accordance with ASC 820 - Fair Value Measurements, certain investments that were measured at net asset value per share (or its equivalent) have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the line items presented in the Consolidated Balance Sheets.
 
Fair Value Measurements
 at December 31, 2023, Using
 
 Quoted Prices
in Active
Markets for
Identical
Assets
 (Level 1)		Significant
Other
Observable
Inputs
 (Level 2)		Significant
Unobservable
 Inputs
 (Level 3)		Balance at December 31, 2023
 (In thousands)
Assets:    
Cash equivalents$— $7,197 $— $7,197 
Equity securities: 
U.S. companies(2)— — (2)
Collective and mutual funds (a)84,761 88,219 — 172,980 
U.S. Government securities30,162 33,141 — 63,303 
Investments measured at net asset value (b)
— — — 5,080 
Total assets measured at fair value$114,921 $128,557 $— $248,558 
(a)Collective and mutual funds invest approximately 51 percent in corporate bonds, 15 percent in common stock of international companies, 11 percent in common stock of large-cap and mid-cap U.S. companies, 7 percent cash and cash equivalents, 7 percent in U.S. Government securities and 9 percent in other investments.
(b)In accordance with ASC 820 - Fair Value Measurements, certain investments that were measured at net asset value per share (or its equivalent) have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the line items presented in the Consolidated Balance Sheets.
The estimated fair values of the Company's other postretirement benefit plans' assets are determined using the market approach.
The estimated fair value of the other postretirement benefit plans' Level 2 cash equivalents is valued at the net asset value of shares held at year end, based on published market quotations on active markets, or using other known sources including pricing from outside sources. The estimated fair value of the other postretirement benefit plans' Level 1 and Level 2 equity securities is based on the closing price reported on the active market on which the individual securities are traded or other known sources including pricing from outside sources. The estimated fair value of the other postretirement benefit plans' Level 2 insurance contract is based on contractual cash surrender values that are determined primarily by investments in managed separate accounts of the insurer. These amounts approximate fair value. The managed separate accounts are valued based on other observable inputs or corroborated market data.
Though the Company believes the methods used to estimate fair value are consistent with those used by other market participants, the use of other methods or assumptions could result in a different estimate of fair value.
The fair value of the Company's other postretirement benefit plans' assets (excluding cash) by asset class were as follows:
 Fair Value Measurements
 at December 31, 2024, Using		 
 Quoted Prices
in Active
Markets for
Identical
Assets
 (Level 1)		Significant
Other
Observable
Inputs
 (Level 2)		Significant
Unobservable
 Inputs
 (Level 3)		Balance at December 31, 2024
 (In thousands)
Assets:    
Cash equivalents$— $4,373 $— $4,373 
Equity securities: 
U.S. companies2,880 — — 2,880 
Insurance contract (a)— 71,512 — 71,512 
Total assets measured at fair value$2,880 $75,885 $— $78,765 
(a)The insurance contract invests approximately 41 percent in corporate bonds, 28 percent in U.S. Government securities, 19 percent in common stock of large-cap U.S. companies, 6 percent in common stock of small-cap U.S. companies and 6 percent in other investments.
 Fair Value Measurements
 at December 31, 2023, Using		 
 Quoted Prices
in Active
Markets for
Identical
Assets
 (Level 1)		Significant
Other
Observable
Inputs
 (Level 2)		Significant
Unobservable
 Inputs
 (Level 3)		Balance at December 31, 2023
 (In thousands)
Assets:    
Cash equivalents$— $4,562 $— $4,562 
Equity securities: 
U.S. companies2,369 — — 2,369 
Insurance contract (a)— 72,303 — 72,303 
Total assets measured at fair value$2,369 $76,865 $— $79,234 
(a)The insurance contract invests approximately 60 percent in corporate bonds, 16 percent in common stock of large-cap U.S. companies, 15 percent in U.S. Government securities, 5 percent in common stock of small-cap U.S. companies and 4 percent in other investments.
Nonqualified benefit plans
In addition to the qualified defined benefit pension plans reflected in the table at the beginning of this note, the Company also has unfunded, nonqualified defined benefit plans for executive officers and certain key management employees that generally provide for defined benefit payments at age 65 following the employee's retirement or, upon death, to their beneficiaries for a 15-year period. In February 2016, the Company froze the unfunded, nonqualified defined benefit plans to new participants and eliminated benefit increases. Vesting for participants not fully vested was retained.
The projected benefit obligation and accumulated benefit obligation for these plans at December 31 were as follows:
 2024 2023 
 (In thousands)
Projected benefit obligation$52,007 $57,033 
Accumulated benefit obligation$52,007 $57,033 
The components of net periodic benefit cost are included in other income on the Consolidated Statements of Income. These components related to the Company's nonqualified defined benefit plans for the years ended December 31 were as follows:
 2024 2023 2022 
 (In thousands)
Components of net periodic benefit cost:   
Interest cost$2,568 $2,740 $1,681 
Recognized net actuarial loss365 273 911 
Net periodic benefit cost$2,933 $3,013 $2,592 
Weighted average assumptions used at December 31 were as follows:
 2024 2023 
Benefit obligation discount rate5.26 %4.73 %
Benefit obligation rate of compensation increaseN/AN/A
Net periodic benefit cost discount rate4.73 %4.97 %
Net periodic benefit cost rate of compensation increaseN/AN/A
The amount of future benefit payments for the unfunded, nonqualified defined benefit plans at December 31, 2024, are expected to aggregate as follows:
202520262027202820292030-2034
(In thousands)
Nonqualified benefits$5,700 $5,610 $5,830 $5,560 $5,190 $20,920 
In 2012, the Company established a nonqualified defined contribution plan for certain key management employees. In 2020, the plan was frozen to new participants and no new Company contributions will be made to the plan after December 31, 2020. Vesting for participants not fully vested was retained. A new nonqualified defined contribution plan was adopted in 2020, effective January 1, 2021, to replace the plan originally established in 2012 with similar provisions. Expenses incurred under these plans for 2024, 2023 and 2022 were $4.0 million, $2.7 million and $538,000, respectively.
The amount of investments that the Company anticipates using to satisfy obligations under these plans at December 31 was as follows:
2024 2023 
(In thousands)
Investments
Insurance contracts*$59,282 $62,936 
Life insurance**30,834 31,303 
Other12,879 6,409 
Total investments$102,995 $100,648 
*For more information on the insurance contracts, see Note 9.
**Investments of life insurance are carried on plan participants (payable upon the employee's death).
Defined contribution plans
The Company sponsors a defined contribution plan for eligible employees and the costs incurred under this plan were $10.7 million in 2024, $17.0 million in 2023 and $14.3 million in 2022.
Multiemployer plans
The Company contributes to a MEPP under the terms of a collective-bargaining agreement that covers its union-represented employees. The risks of participating in this multiemployer plan is different from single-employer plans in the following aspects:
•Assets contributed to the MEPP by one employer may be used to provide benefits to employees of other participating employers
•If a participating employer stops contributing to the plan, the unfunded obligations of the plan may be borne by the remaining participating employers
•If the Company chooses to stop participating in its MEPP, the Company may be required to pay those plans an amount based on the underfunded status of the plan, referred to as a withdrawal liability
The Company's participation in this plan is outlined in the following table. Unless otherwise noted, the most recent Pension Protection Act zone status available in 2024 and 2023 is for the plan's year-end status at December 31, 2023, and December 31, 2022, respectively. The zone status is based on information that the Company received from the plan and is certified by the plan's actuary. Among other factors, a plan in the red zone is generally less than 65 percent funded, a plan in the yellow zone is between 65 percent and 80 percent funded, and a plan in the green zone is at least 80 percent funded.
EIN/Pension Plan NumberPension Protection Act Zone StatusFIP/RP Status Pending/ImplementedContributionsSurcharge ImposedExpiration Date
of Collective
Bargaining
Agreement
Pension Fund202420232024 2023 2022 
(In thousands)
Idaho Plumbers and Pipefitters Pension Plan
826010346-001
Green as of 5/31/2024
Green as of 5/31/2023
No$1,434 $1,690 $1,613 No3/31/2027
Total contributions$1,434 $1,690 $1,613 
The Company was listed in the plans' Forms 5500 as providing more than 5 percent of the total contributions for the following plans and plan years:
Pension FundYear Contributions to Plan Exceeded More Than 5 Percent
of Total Contributions (as of December 31 of the Plan's Year-End)
Idaho Plumbers and Pipefitters Pension Plan2023 and 2022
v3.25.0.1
Regulatory Matters
 12 Months Ended
Dec. 31, 2024
Regulated Operations [Abstract]  
Regulatory Matters Regulatory Matters
The Company regularly reviews the need for electric and natural gas rate changes in each of the jurisdictions in which service is provided. The Company files for rate adjustments to seek recovery of operating costs and capital investments, as well as reasonable returns as allowed by regulators. Certain regulatory proceedings and cases may also contain recurring mechanisms that can have an annual true-up. Examples of these recurring mechanisms include: infrastructure riders, transmission trackers, renewable resource cost adjustment riders, as well as weather normalization and decoupling mechanisms. The following paragraphs summarize the Company's significant open regulatory proceedings and cases by jurisdiction. The Company is unable to predict the ultimate outcome of these matters, the timing of final decisions of the various regulators and courts, or the effect on the Company's results of operations, financial position or cash flows.

MTPSC
On July 15, 2024, Montana-Dakota filed a request with the MTPSC for a natural gas general rate increase of approximately $9.4 million annually or 11.1 percent above current rates. The requested increase is primarily to recover investments in system upgrades and pipeline replacement projects enhancing the reliability, safety and integrity of the natural gas system, as well as increased costs to operate and maintain that system. On October 15, 2024, the MTPSC denied Montana-Dakota's request for an interim rate increase of approximately $8.0 million annually or 10.2 percent above current rates. On October 25, 2024, Montana-Dakota filed a motion for reconsideration of the interim rate increase. On January 14, 2025, the MTPSC approved an interim increase of approximately $7.7 million with interim rates effective on and after February 1, 2025.
NDPSC
On November 1, 2023, Montana-Dakota filed a request with the NDPSC for a natural gas general rate increase of approximately $11.6 million annually or 7.5 percent above current rates. The requested increase is primarily to recover investments in system upgrades and pipeline replacement projects enhancing the reliability, safety and integrity of the natural gas system, as well as increased costs to operate and maintain that system. On December 13, 2023, the NDPSC approved an interim rate increase of approximately $10.1 million annually or 6.5 percent above current rates, subject to refund, for service rendered on and after January 1, 2024. On September 16, 2024, an all-party settlement agreement was filed reflecting an annual revenue increase of $9.4 million or 6.1 percent overall. The reduction from the original filing includes lower incentives and a decreased return on equity. On November 7, 2024, the NDPSC approved the settlement with rates effective on and after December 1, 2024.
Montana-Dakota has a renewable resource cost adjustment rate tariff that allows for annual adjustments for recent projected capital costs and related expenses for projects determined to be recoverable under the tariff. On November 1, 2024, Montana-Dakota filed an annual update to its renewable resource cost adjustment requesting to recover a revenue requirement of approximately $18.3 million annually. The update reflects a decrease of approximately $2.8 million annually from the revenues currently included in rates. The NDPSC approved the renewable resource cost adjustment on January 22, 2025, with rates effective February 1, 2025.

WUTC
On March 29, 2024, Cascade filed a request with the WUTC for a multi-year natural gas general rate increase of $43.8 million or 11.6 percent effective March 1, 2025 and $11.7 million or 2.8 percent to be effective March 1, 2026. Multi-year filings are now required by Washington law that went into effect on January 1, 2022. The requested increase is primarily to recover infrastructure investments necessary to provide safe and reliable service and higher operating costs due to inflation. On December 11, 2024, a multi-party settlement agreement was filed reflecting rate increases of $29.8 million or 7.9 percent proposed to be effective March 1, 2025, and $10.8 million or 2.6 percent proposed to be effective March 1, 2026.

WYPSC
On October 31, 2024, Montana-Dakota filed a request with the WYPSC for a natural gas general rate increase of approximately $2.6 million annually or 14.0 percent above current rates. The requested increase is primarily to recover investments in system upgrades and pipeline replacement projects enhancing the reliability, safety and integrity of the natural gas system, as well as increased costs to operate and maintain that system. This matter is pending before the WYPSC.

FERC
On August 29, 2024, Montana-Dakota filed an update to its transmission formula rate under the MISO tariff for its multi-value project and network upgrade changes for $19.7 million. Rates were effective January 1, 2025.
v3.25.0.1
Commitments and Contingencies
 12 Months Ended
Dec. 31, 2024
Commitments and Contingencies Disclosure [Abstract]  
Commitments and Contingencies Commitments and Contingencies
The Company is party to claims and lawsuits arising out of its business and that of its consolidated subsidiaries, which may include, but are not limited to, matters involving property damage, personal injury, and environmental, contractual, statutory and regulatory obligations. The Company accrues a liability for those contingencies when the incurrence of a loss is probable and the amount can be reasonably estimated. If a range of amounts can be reasonably estimated and no amount within the range is a better estimate than any other amount, then the minimum of the range is accrued. The Company does not accrue liabilities when the likelihood that the liability has been incurred is probable but the amount cannot be reasonably estimated or when the liability is believed to be only reasonably possible or remote. For contingencies where an unfavorable outcome is probable or reasonably possible and which are material, the Company discloses the nature of the contingency and, in some circumstances, an estimate of the possible loss. Accruals are based on the best information available, but in certain situations management is unable to estimate an amount or range of a reasonably possible loss including, but not limited to when: (1) the damages are unsubstantiated or indeterminate, (2) the proceedings are in the early stages, (3) numerous parties are involved, or (4) the matter involves novel or unsettled legal theories.
At December 31, 2024 and 2023, the Company accrued liabilities which have not been discounted of $24.1 million and $22.5 million, respectively. At December 31, 2024 and 2023, the Company also recorded corresponding insurance receivables of $24,000 and $152,000, respectively, and regulatory assets of $22.9 million and $21.6 million, respectively, related to the accrued liabilities. The accruals are for contingencies resulting from litigation and environmental matters. This includes amounts that have been accrued for matters discussed in Environmental matters within this note. The Company will continue to monitor each matter and adjust accruals as might be warranted based on new information and further developments. Management believes that the outcomes with respect to probable and reasonably possible losses in excess of the amounts accrued, net of insurance recoveries, while uncertain, either cannot be estimated or will not have a material effect upon the Company's financial position, results of operations or cash flows. Unless otherwise required by GAAP, legal costs are expensed as they are incurred.
Environmental matters
Manufactured Gas Plant Sites Claims have been made against Cascade for cleanup of environmental contamination at manufactured gas plant sites operated by Cascade's predecessors and a similar claim has been made against Montana-Dakota for a site operated by Montana-Dakota and its predecessors. Any accruals related to these claims are reflected in regulatory assets. For more information, see Note 6.
Demand has been made of Montana-Dakota to participate in investigation and remediation of environmental contamination at a site in Missoula, Montana. The site operated as a former manufactured gas plant from approximately 1907 to 1938 when it was converted to a butane-air plant that operated until 1956. Montana-Dakota or its predecessors owned or controlled the site for a period of the time it operated as a manufactured gas plant and Montana-Dakota operated the butane-air plant from 1940 to 1951, at which time it sold the plant. There are no documented wastes or by-products resulting from the mixing or distribution of butane-air gas. Preliminary assessment of a portion of the site provided a recommended remedial alternative for that portion of approximately $560,000. However, the recommended remediation would not address any potential contamination to adjacent parcels that may be impacted from historic operations of the manufactured gas plant. An environmental assessment, which was started in 2020 and is still underway, is estimated to cost approximately $2.0 million. Montana-Dakota and another party agreed to voluntarily investigate and remediate the site and that Montana-Dakota will pay two-thirds of the costs for further investigation and remediation of the site. Montana-Dakota has accrued costs of $645,000 for the remediation and investigation costs and has incurred costs of $1.2 million as of December 31, 2024. Montana-Dakota received notice from a prior insurance carrier that it will participate in payment of defense costs incurred in relation to the claim. On December 9, 2021, Montana Dakota filed an application with the MTPSC for deferred accounting treatment for costs associated with the investigation and remediation of the site. The MTPSC approved the application for deferred accounting treatment as requested on July 26, 2022.
A claim was made against Cascade for contamination at the Bremerton Gasworks Superfund Site in Bremerton, Washington, which was received in 1997. A preliminary investigation has found soil and groundwater at the site contain impacts requiring further investigation and cleanup. The EPA conducted a Targeted Brownfields Assessment of the site and released a report summarizing the results of that assessment in August 2009. The assessment confirmed that impacts have affected soil and groundwater at the site, as well as sediments in the adjacent Port Washington Narrows. In April 2010, the Washington DOE issued notice it considered Cascade a PRP for hazardous substances at the site. In May 2012, the EPA added the site to the National Priorities List of Superfund sites. Cascade entered into an administrative settlement agreement and consent order with the EPA regarding the scope and schedule for a remedial investigation and feasibility study for the site. Current estimates for the cost to complete the remedial investigation and feasibility study are approximately $16.0 million of which $11.7 million has been incurred as of December 31, 2024. Based on the site investigation, preliminary remediation alternative costs were provided by consultants in August 2020. The preliminary information received through the completion of the data report allowed for the projection of possible costs for a variety of site configurations, remedial measures and potential natural resource damage claims of between $13.6 million and $71.5 million. At December 31, 2024, Cascade has accrued $4.3 million for the remedial investigation and feasibility study, as well as $17.5 million for remediation of this site. The accrual for remediation costs will be reviewed and adjusted, if necessary, after the completion of the feasibility study. In April 2010, Cascade filed a petition with the WUTC for authority to defer the costs incurred in relation to the environmental remediation of this site. The WUTC approved the petition in September 2010, subject to conditions set forth in the order. A significant portion of the costs incurred to date have been recovered by insurance.
A claim was made against Cascade for impacts at a site in Bellingham, Washington. Cascade received notice from a party in May 2008 that Cascade may be a PRP, along with other parties, for impacts from a manufactured gas plant owned by Cascade and its predecessor from about 1946 to 1962. Other PRPs reached an agreed order and work plan with the Washington DOE for completion of a remedial investigation and feasibility study for the site. A feasibility study prepared for one of the PRPs in March 2018 identifies five cleanup action alternatives for the site with estimated costs ranging from $8.0 million to $20.4 million with a selected preferred alternative having an estimated total cost of $9.3 million. The other PRPs developed a cleanup action plan and completed public review in 2020. The development of the remediation design is underway, with the Pre-Remedial Design Investigation Data Report and Engineering Design Report submitted to Washington Ecology in June 2023 and November 2024, respectively. The remedy construction is expected to commence in 2028 following the approval of the final design. Cascade believes its proportional share of any liability will be relatively small in comparison to other PRPs. The plant manufactured gas from coal between approximately 1890 and 1946. In 1946, shortly after Cascade's predecessor acquired the plant, the plant converted to a propane-air gas facility. There are no documented wastes or by-products resulting from the mixing or distribution of propane-air gas. Cascade has recorded an accrual for this site for an amount that is not material.
The Company has received notices from and entered into agreements with certain of its insurance carriers that they will participate in the defense for certain contamination claims subject to full and complete reservations of rights and defenses to insurance coverage. To the extent these claims are not covered by insurance, the Company intends to seek recovery of remediation costs through its natural gas rates charged to customers.
Purchase commitments
The Company has entered into various commitments largely consisting of contracts for natural gas and coal supply; purchased power; natural gas transportation and storage; and information technology. Certain of these contracts are subject to variability in volume and price. The commitment terms vary in length, up to 35 years. The commitments under these contracts as of December 31, 2024, were:
20252026202720282029Thereafter
(In thousands)
Purchase commitments$658,012 $310,894 $210,152 $177,613 $147,081 $1,221,125 
These commitments were not reflected in the Company's consolidated financial statements. Amounts purchased under various commitments for the years ended December 31, 2024, 2023 and 2022, were $841.7 million, $1.0 billion and $870.6 million, respectively.
Guarantees
The Company and certain subsidiaries have outstanding letters of credit to third parties related to insurance policies and other agreements, some of which are guaranteed by other subsidiaries of the Company. At December 31, 2024, the fixed maximum amounts guaranteed under these letters of credit aggregated $14.3 million. The amounts of scheduled expiration of the maximum amounts guaranteed under these letters of credit aggregate to $14.3 million in 2025. There were no amounts outstanding under the previously mentioned letters of credit at December 31, 2024. In the event of default under these letter of credit obligations, the Company or subsidiary guaranteeing the letter of credit would be obligated for reimbursement of payments made under the letter of credit.
In the normal course of business, the Company and its subsidiaries have surety bonds. In the event the Company or its subsidiaries do not fulfill a bonded obligation, the Company or its subsidiaries would be responsible to the surety bond company for completion of the bonded contract or obligation. At December 31, 2024, approximately $15.6 million of surety bonds were outstanding, which were not reflected on the Consolidated Balance Sheet.
Leases
Most of the leases the Company enters into are for equipment, buildings, easements and vehicles as part of their ongoing operations. The Company also leases certain equipment to third parties through its utility business. The Company determines if an arrangement contains a lease at inception of a contract and accounts for all leases in accordance with ASC 842 - Leases.
The recognition of leases requires the Company to make estimates and assumptions that affect the lease classification and the assets and liabilities recorded. The accuracy of lease assets and liabilities reported on the Consolidated Financial Statements depends on, among other things, management's estimates of interest rates used to discount the lease assets and liabilities to their present value, as well as the lease terms based on the unique facts and circumstances of each lease.
Lessee accounting The leases the Company has entered into as part of its ongoing operations are considered operating leases and are recognized on the Consolidated Balance Sheets as noncurrent assets - other, current liabilities - other accrued liabilities and noncurrent liabilities - other. The corresponding lease costs are included in operation and maintenance expense on the Consolidated Statements of Income.
Generally, the leases for equipment have a term of five years or less and buildings and easements have a longer term of up to 35 years or more. To date, the Company does not have any residual value guarantee amounts probable of being owed to a lessor, financing leases or material agreements with related parties.
The following tables provide information on the Company's operating leases at and for the years ended December 31:
202420232022
(In thousands)
Lease costs:
Short-term lease cost$1,549 $1,646 $1,373 
Operating lease cost3,069 2,871 2,497 
Variable lease cost819 676 413 
$5,437 $5,193 $4,283 
202420232022
(Dollars in thousands)
Weighted average remaining lease term12.65 years15.35 years15.15 years
Weighted average discount rate6.08 %4.88 %4.65 %
Cash paid for amounts included in the measurement of lease liabilities
$3,063$2,868 $2,500 
The reconciliation of future undiscounted cash flows to operating lease liabilities presented on the Consolidated Balance Sheet at December 31, 2024, was as follows:
(In thousands)
2025$3,034 
20262,648 
20272,011 
20281,570 
20291,492 
Thereafter20,808 
Total31,563 
Less discount10,654 
Total operating lease liabilities$20,909 
Lessor accounting The Company leases certain equipment to third parties through its utility businesses, which are considered short-term operating leases with terms of less than 12 months. Lease revenue was not material for the years ended December 31, 2024, 2023 and 2022, respectively.
Variable interest entities
The Company evaluates its arrangements and contracts with other entities to determine if they are VIEs and if so, if the Company is the primary beneficiary.
Fuel Contract Coyote Station entered into a coal supply agreement with Coyote Creek that provides for the purchase of coal necessary to supply the coal requirements of the Coyote Station for the period May 2016 through December 2040. Coal purchased under the coal supply agreement is reflected in Inventories on the Consolidated Balance Sheets and is recovered from customers as a component of electric fuel and purchased power.
The coal supply agreement creates a variable interest in Coyote Creek due to the transfer of all operating and economic risk to the Coyote Station owners, as the agreement is structured so that the price of the coal will cover all costs of operations, as well as future reclamation costs. The Coyote Station owners are also providing a guarantee of the value of the assets of Coyote Creek as they would be required to buy the assets at book value should they terminate the contract prior to the end of the contract term and are providing a guarantee of the value of the equity of Coyote Creek in that they are required to buy the entity at the end of the contract term at equity value. Although the Company has determined that Coyote Creek is a VIE, the Company has concluded that it is not the primary beneficiary of Coyote Creek because the authority to direct the activities of the entity is shared by the four unrelated owners of the Coyote Station, with no primary beneficiary existing. As a result, Coyote Creek is not required to be consolidated in the Company's financial statements.
At December 31, 2024, the Company's exposure to loss as a result of the Company's involvement with the VIE, based on the Company's ownership percentage, was $25.6 million.
v3.25.0.1
Subsequent Events
 12 Months Ended
Dec. 31, 2024
Subsequent Events [Abstract]  
Subsequent Events Subsequent EventsOn February 13, 2025, Montana-Dakota entered into a definitive purchase and sale agreement with Badger Wind, LLC, a subsidiary of Orsted Onshore North America, LLC. Pursuant to the terms of the agreement, Montana-Dakota will purchase a 49 percent undivided ownership interest in a wind project being constructed and located in North Dakota that is anticipated to have a net generating capacity of approximately 250 MW for a purchase price of $294.0 million, which would represent 122.5 MW of wind generation to be owned by Montana-Dakota. The purchase agreement is contingent on regulatory approval from the NDPSC. This transaction would reduce Montana-Dakota's purchase requirements under the existing power purchase agreement with Badger Wind, LLC, dated November 4, 2024.
v3.25.0.1
Schedule I - Condensed Financial Information of Registrant
 12 Months Ended
Dec. 31, 2024
Condensed Financial Information Disclosure [Abstract]  
Schedule I-Condensed Financial Information of Registrant Condensed Financial Information of Registrant (Unconsolidated)
Condensed Statements of Income and Comprehensive Income
Years ended December 31,202420232022
 (In thousands)
Operating revenues$— $— $— 
Operating expenses4,416 9,668 1,636 
Operating loss(4,416)(9,668)(1,636)
Realized gain on tax-free exchange of the retained shares in Knife River— 186,556 — 
Interest expense642 7,109 — 
Income (loss) before income taxes
(5,058)169,779 (1,636)
Income tax benefit
(2,324)(4,220)(400)
Equity in earnings of subsidiaries from continuing operations183,807 156,118 118,488 
Income from continuing operations181,073 330,117 117,252 
Equity in earnings of subsidiaries from discontinued operations
140,042 143,181 261,701 
Discontinued operations, net of tax
(40,007)(58,591)(11,464)
Net income$281,108 $414,707 $367,489 
Comprehensive income$282,694 $414,600 $377,910 
The accompanying notes are an integral part of these condensed financial statements.
Condensed Financial Information of Registrant (Unconsolidated)
Condensed Balance Sheets
December 31,20242023
(In thousands, except shares and per share amounts)
Assets  
Current assets:  
Cash and cash equivalents$29,361 $33,039 
Receivables, net2,777 6,568 
Accounts receivable from subsidiaries31,955 30,526 
Taxes receivable
5,799 — 
Prepayments and other current assets3,210 8,261 
Total current assets73,102 78,394 
Noncurrent assets
Investments37,264 37,722 
Investment in subsidiaries2,861,311 3,146,122 
Notes receivable from subsidiaries
— 58,000 
Deferred income taxes13,569 12,596 
Operating lease right-of-use assets160 31 
Other2,874 2,593 
Total noncurrent assets2,915,178 3,257,064 
Total assets$2,988,280 $3,335,458 
Liabilities and Stockholders' Equity
Current liabilities:
Accounts payable$4,076 $4,264 
Accounts payable to subsidiaries1,077 3,435 
Notes payable to subsidiaries
198,035 134,107 
Taxes payable— 542 
Dividends payable26,511 25,461 
Accrued compensation7,939 9,651 
Operating lease liabilities due within one year60 25 
Other accrued liabilities7,653 8,008 
Total current liabilities245,351 185,493 
Noncurrent liabilities:
Long-term debt, net of debt issuance costs
(536)57,048 
Operating lease liabilities100 6 
Other52,791 187,678 
Total noncurrent liabilities52,355 244,732 
Commitments and contingencies
Stockholders' equity:  
Common stock
Authorized - 500,000,000 shares, $1.00 par value
Shares issued - 203,934,578 at December 31, 2024 and 203,689,090 at December 31, 2023
203,935 203,689 
Other paid-in capital1,473,738 1,466,235 
Retained earnings1,029,699 1,253,693 
Accumulated other comprehensive loss(16,798)(18,384)
Total stockholders' equity2,690,574 2,905,233 
Total liabilities and stockholders' equity$2,988,280 $3,335,458 
The accompanying notes are an integral part of these condensed financial statements.
Condensed Financial Information of Registrant (Unconsolidated)
Condensed Statements of Cash Flows
Years ended December 31,2024 2023 2022 
 (In thousands)
Net cash provided by operating activities of continuing operations
$482,195 $282,132 $253,663 
Net cash used in operating activities of discontinued operations
(40,007)(58,591)(11,464)
Net cash provided by operating activities
442,188 223,541 242,199 
Investing activities:  
Investments in and advances to subsidiaries(211,000)(476,000)(45,000)
Investments2,253 7,422 (885)
Repayment (issuance) of notes receivable
58,000 (58,000)— 
Net cash used in investing activities of continuing operations
(150,747)(526,578)(45,885)
Financing activities:  
Issuance of short-term borrowings— 535,000 — 
Repayment of short-term borrowings— (242,401)— 
Issuance of long-term debt— 443,000 — 
Repayment of long-term debt(58,000)(385,000)— 
Debt issuance costs
(401)(952)— 
Proceeds from issuance of common stock(50)— (149)
Dividends paid(102,939)(161,316)(176,915)
Repurchase of common stock— (2,270)(3,525)
Tax withholding on stock-based compensation(1,729)(1,471)(2,398)
Net cash provided by (used in) financing activities of continuing operations
(163,119)184,590 (182,987)
Net cash provided by (used in) financing activities of discontinued operations
(132,000)132,000 — 
Net cash provided by (used in) financing activities
(295,119)316,590 (182,987)
Increase (decrease) in cash and cash equivalents(3,678)13,553 13,327 
Cash and cash equivalents - beginning of year33,039 19,486 6,159 
Cash and cash equivalents - end of year$29,361 $33,039 $19,486 
The accompanying notes are an integral part of these condensed financial statements.
Note 1 - Summary of Significant Accounting Policies
Basis of presentation The condensed financial information reported in Schedule I is being presented to comply with Rule 12-04 of Regulation S-X. The information is unconsolidated and is presented for the parent company only, MDU Resources Group, Inc. (the Company) as of and for the years ended December 31, 2024, 2023 and 2022. In Schedule I, investments in subsidiaries are presented under the equity method of accounting where the assets and liabilities of the subsidiaries are not consolidated. The investments in net assets of the subsidiaries are recorded on the Condensed Balance Sheets. The income from subsidiaries is reported as equity in earnings of subsidiaries on the Condensed Statements of Income. The material cash inflows on the Condensed Statements of Cash Flows are primarily from the dividends and other payments received from its subsidiaries and the proceeds raised from the issuance of debt and equity securities. The consolidated financial statements of the Company reflect certain businesses as discontinued operations. These statements should be read in conjunction with the consolidated financial statements and notes thereto of the Company.
Earnings per common share Please refer to the Consolidated Statements of Income of the registrant for earnings per common share. In addition, see Item 8 - Note 2 for information on the computation of earnings per common share.
Note 2 - Debt
MDU Resources Group, Inc. On May 31, 2023, the Company entered into a $150.0 million revolving credit agreement with a SOFR-based variable interest rate and a maturity date of May 29, 2024. At December 31, 2023, the Company had no amount outstanding, which remained that way until this agreement matured and subsequently terminated in May 2024.
On May 31, 2023, the Company entered into a $200.0 million revolving credit agreement with a SOFR-based variable interest rate and a maturity date of May 31, 2028. Any borrowings under the revolving credit agreement are classified as long-term debt as they are intended to be refinanced on a long-term basis through continued borrowings. The credit agreement contains customary covenants and provisions, including a covenant of the Company not to permit, at any time, the ratio of total debt to total capitalization to be greater than 65 percent. The covenants also include certain restrictions on the sale of certain assets, loans and investments. At December 31, 2024, there were no amounts outstanding under the agreement.
On May 31, 2023, the Company entered into a $375.0 million term loan agreement with a SOFR-based variable interest rate and a maturity date of May 31, 2025. On November 15, 2023, the Company paid down $185.0 million of the term loan agreement. On November 1, 2024, the Company repaid its remaining outstanding balance of $190.0 million and the term loan agreement subsequently terminated. The Company's repayment was funded by the Everus repayment of debt in connection with the separation. Refer to Note 3 for additional information related to the repayment of debt associated with the Everus separation.
At December 31, 2024, the Company had no long-term debt maturities for 2025. For more information on debt, see Item 8 - Note 10.
Note 3 - Dividends The Company depends on earnings and dividends from its subsidiaries to pay dividends on common stock. Cash dividends paid to the Company by subsidiaries were $418.3 million, $165.5 million and $242.1 million for the years ended December 31, 2024, 2023 and 2022, respectively.
v3.25.0.1
Jointly Owned Facilities
 12 Months Ended
Dec. 31, 2024
Regulated Operations [Abstract]  
Jointly Owned Facilities Jointly Owned Facilities
The consolidated financial statements include the Company's ownership interests in three coal-fired electric generating facilities (Big Stone Station, Coyote Station and Wygen III) and two major transmission lines (BSSE and JETx). Each owner of the jointly owned facilities is responsible for financing its investment. The Company's share of the jointly owned facilities operating expenses was reflected in the appropriate categories of operating expenses (electric fuel and purchased power; operation and maintenance; and taxes, other than income) in the Consolidated Statements of Income.
At December 31, the Company's share of the cost of utility plant in service, construction work in progress and related accumulated depreciation for the jointly owned facilities was as follows:
Ownership Percentage20242023
 (In thousands)
Big Stone Station:22.7 %
Utility plant in service$155,302 $159,437 
CWIP
318 197 
Less accumulated depreciation55,327 52,264 
$100,293 $107,370 
BSSE:50.0 %
Utility plant in service$111,043 $107,260 
CWIP
— — 
Less accumulated depreciation10,359 8,111 
$100,684 $99,149 
Coyote Station:25.0 %
Utility plant in service$160,343 $160,208 
CWIP
755 159 
Less accumulated depreciation115,133 113,187 
$45,965 $47,180 
JETx:
50.0 %
Utility plant in service$— $— 
CWIP
6,112 1,372 
Less accumulated depreciation— — 
$6,112 $1,372 
Wygen III:25.0 %
Utility plant in service$67,851 $66,852 
CWIP
97 127 
Less accumulated depreciation15,340 13,728 
$52,608 $53,251 
v3.25.0.1
Pay vs Performance Disclosure - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Pay vs Performance Disclosure      
Net income $ 281,108 $ 414,707 $ 367,489
v3.25.0.1
Insider Trading Arrangements
 3 Months Ended
Dec. 31, 2024
Trading Arrangements, by Individual  
Rule 10b5-1 Arrangement Adopted false
Non-Rule 10b5-1 Arrangement Adopted false
Rule 10b5-1 Arrangement Terminated false
Non-Rule 10b5-1 Arrangement Terminated false
v3.25.0.1
Insider Trading Policies and Procedures
 12 Months Ended
Dec. 31, 2024
Insider Trading Policies and Procedures [Line Items]  
Insider Trading Policies and Procedures Adopted true
v3.25.0.1
Cybersecurity Risk Management and Strategy Disclosure
 12 Months Ended
Dec. 31, 2024
Cybersecurity Risk Management, Strategy, and Governance [Line Items]  
Cybersecurity Risk Management Processes for Assessing, Identifying, and Managing Threats [Text Block]
Overall Risk Management
The Company has implemented a cyber risk management program to help ensure that the Company's electronic information and information systems are protected from various threats. The cyber risk management program is maintained as part of the Company's overall governance, ERM program and compliance program. The Company's information systems experience ongoing and often sophisticated cyberattacks by a variety of sources with the apparent aim to breach the Company's cyber-defenses. The Company has and may continue to face increased cyber risk due to the increased use of employee-owned devices and work from home arrangements. The Company is continuously reevaluating the need to upgrade and/or replace systems and network infrastructure. These upgrades and/or replacements could adversely impact operations by imposing substantial capital expenditures, creating delays or outages, or experiencing difficulties transitioning to new systems. System disruptions, if not anticipated and appropriately mitigated, could adversely affect the Company. The Company continually assesses risks from cybersecurity threats and adapts and enhances its controls accordingly.
Risks from Cybersecurity Threats
Any risks from previous cybersecurity threats, including as a result of any previous cybersecurity incidents, have not materially affected or are reasonably likely to materially affect the Company's business, financial condition, or results of operations. Such risks and incidents could have a material adverse effect in the future as cyberattacks continue to increase in frequency and sophistication. The Company also has cyber event related insurance.
Employee Cybersecurity Training
The Company provides ongoing cybersecurity training and compliance programs to facilitate education for employees who may have access to the Company's data and critical systems. Employee phishing tests are conducted on a monthly basis.
Engage Third-parties on Risk Management
Periodic external reviews, including penetration tests and security framework assessments, are conducted by auditors, external assessors, and/or consultants to assess and ensure compliance with the Company’s information security programs and practices. Internal and external auditors assess the Company’s information technology general controls on an annual basis.
Oversee Third-party Risk
The Company has implemented a third-party management risk program to help monitor and reduce risks associated with the Company's vendors, which includes processes such as completing due diligence on third party service providers before engaging with them for their services; assessing the third party’s cybersecurity posture by reviewing audit reports of the third party, completing cyber questionnaires, and reviewing applicable certification; including cybersecurity contractual language in contracts to limit risk; and monitoring and reassessing third party’s to ensure ongoing compliance with their cybersecurity obligations.
Physical Security
The Company safeguards assets through a standard physical security design process, including access controls, surveillance and monitoring, perimeter security controls, data center security, and incident response and reporting controls.
Operational Technology
The Company has operation technology, consisting of the hardware and software that monitors and controls devices, processes, and infrastructure related to the Company's operational assets. Security protocols for the Company's operational technology follow applicable NERC, FERC and TSA regulations and security directives.
Other Risk Factors
Notwithstanding the breadth of the Company's information security program, the Company may be unsuccessful in preventing or mitigating a cybersecurity event that could have a material adverse impact. See “Item 1A – Risk Factors – Other Risks – Technology disruptions or cyberattacks could adversely impact the Company's operations.”
Cybersecurity Risk Management Processes Integrated [Flag] true
Cybersecurity Risk Management Processes Integrated [Text Block]
The Company has implemented a cyber risk management program to help ensure that the Company's electronic information and information systems are protected from various threats. The cyber risk management program is maintained as part of the Company's overall governance, ERM program and compliance program. The Company's information systems experience ongoing and often sophisticated cyberattacks by a variety of sources with the apparent aim to breach the Company's cyber-defenses. The Company has and may continue to face increased cyber risk due to the increased use of employee-owned devices and work from home arrangements. The Company is continuously reevaluating the need to upgrade and/or replace systems and network infrastructure. These upgrades and/or replacements could adversely impact operations by imposing substantial capital expenditures, creating delays or outages, or experiencing difficulties transitioning to new systems. System disruptions, if not anticipated and appropriately mitigated, could adversely affect the Company. The Company continually assesses risks from cybersecurity threats and adapts and enhances its controls accordingly.
Cybersecurity Risk Management Third Party Engaged [Flag] true
Cybersecurity Risk Third Party Oversight and Identification Processes [Flag] true
Cybersecurity Risk Materially Affected or Reasonably Likely to Materially Affect Registrant [Flag] false
Cybersecurity Risk Board of Directors Oversight [Text Block]
Board of Directors Oversight
The Company's board of directors, as a whole and through its committees, has responsibility for oversight of risk management. In its risk oversight role, the board of directors has the responsibility to satisfy itself that the risk management processes designed and implemented by management are adequate for identifying, assessing, and managing risk. The audit committee of the board of directors of the Company is responsible for oversight of risks from cybersecurity threats.
Management's Role Managing Risk
The Company's CIO plays a large role in informing the audit committee of the board of directors on cybersecurity risks. The audit committee of the board of directors receives presentations and reports from the CIO on cybersecurity related issues which include information security, technology risks and risk mitigation programs regularly at the quarterly board meetings. In addition to scheduled meetings, the CIO and audit committee of the board of directors maintain an ongoing dialogue regarding emerging or potential cybersecurity risks.
Cybersecurity Incident Response
The Company has an incident response plan to identify, protect, detect, respond to, and recover from cybersecurity threats and incidents that is also tested on an annual basis. The incident response plan is updated based on results of the test or as new cyber related developments occur. The CIO, executive leadership which includes the chief executive officer, chief financial officer, chief accounting officer, chief legal officer, and SEC financial reporting department employees, and the board of directors are notified of any material cybersecurity incidents through a defined escalation process. The defined escalation process is a risk-based process that specifies who is to be contacted and when at each risk level.
Monitor, Manage, and Safeguard Against Cybersecurity Incidents and Risks
The Company's CIO, along with its director of cybersecurity and a designated security team of professionals, are responsible for assessing and managing risks as well as developing and implementing policies, procedures, and practices based on the range of threats faced by the Company. There are processes around access management, data security, encryption, asset management, secure system development, security operations, network and device security to provide safeguards from a cybersecurity incident along with continual monitoring of various threat intelligence feeds.
Cyber Risk Management Personnel
The Company's director of cybersecurity reports to the CIO and the CIO reports directly to the Company's chief executive officer. The Company's CIO who served as the first CIO of the Company since 2016, oversaw the information technology and cybersecurity portfolios until her retirement on January 10, 2025. A new CIO from within the Company was named to succeed the retiring CIO and holds both a bachelor's and master's degree in business administration with over 25 years of information technology experience in the energy and utilities business. The director of cybersecurity has a bachelor’s degree in computer information systems, over 25 years of information security experience, and holds certified information systems security professional and certified risk and information systems control certifications. The other members of information technology director level leadership also responsible for managing cybersecurity risks have degrees including Bachelor of Computer Information Systems, information systems management, electronics, electrical engineering, business administration, and accounting, along with certified information systems auditor certification and a cybersecurity fundamentals certificate.
Cyber Risk Oversight Committee
Additionally, in 2014 the board of directors established CyROC to provide executive management and the audit committee of the board of directors with analyses, appraisals, recommendations and pertinent information concerning cyber defense of the Company's electronic information, information technology and operation technology systems. The CyROC is responsible for guiding the Company's comprehensive cybersecurity policies and oversight of cybersecurity risks. The CyROC is chaired by the Company's CIO and is comprised of members such as the chief financial officer, information technology leaders, internal auditors, and other leaders from across the Company.
Cybersecurity Risk Board Committee or Subcommittee Responsible for Oversight [Text Block] The Company's board of directors, as a whole and through its committees, has responsibility for oversight of risk management. In its risk oversight role, the board of directors has the responsibility to satisfy itself that the risk management processes designed and implemented by management are adequate for identifying, assessing, and managing risk. The audit committee of the board of directors of the Company is responsible for oversight of risks from cybersecurity threats.Additionally, in 2014 the board of directors established CyROC to provide executive management and the audit committee of the board of directors with analyses, appraisals, recommendations and pertinent information concerning cyber defense of the Company's electronic information, information technology and operation technology systems. The CyROC is responsible for guiding the Company's comprehensive cybersecurity policies and oversight of cybersecurity risks. The CyROC is chaired by the Company's CIO and is comprised of members such as the chief financial officer, information technology leaders, internal auditors, and other leaders from across the Company.
Cybersecurity Risk Process for Informing Board Committee or Subcommittee Responsible for Oversight [Text Block]
The Company's CIO plays a large role in informing the audit committee of the board of directors on cybersecurity risks. The audit committee of the board of directors receives presentations and reports from the CIO on cybersecurity related issues which include information security, technology risks and risk mitigation programs regularly at the quarterly board meetings. In addition to scheduled meetings, the CIO and audit committee of the board of directors maintain an ongoing dialogue regarding emerging or potential cybersecurity risks.
Cybersecurity Risk Role of Management [Text Block]
The Company's CIO plays a large role in informing the audit committee of the board of directors on cybersecurity risks. The audit committee of the board of directors receives presentations and reports from the CIO on cybersecurity related issues which include information security, technology risks and risk mitigation programs regularly at the quarterly board meetings. In addition to scheduled meetings, the CIO and audit committee of the board of directors maintain an ongoing dialogue regarding emerging or potential cybersecurity risks.
Cybersecurity Incident Response
The Company has an incident response plan to identify, protect, detect, respond to, and recover from cybersecurity threats and incidents that is also tested on an annual basis. The incident response plan is updated based on results of the test or as new cyber related developments occur. The CIO, executive leadership which includes the chief executive officer, chief financial officer, chief accounting officer, chief legal officer, and SEC financial reporting department employees, and the board of directors are notified of any material cybersecurity incidents through a defined escalation process. The defined escalation process is a risk-based process that specifies who is to be contacted and when at each risk level.
Monitor, Manage, and Safeguard Against Cybersecurity Incidents and Risks
The Company's CIO, along with its director of cybersecurity and a designated security team of professionals, are responsible for assessing and managing risks as well as developing and implementing policies, procedures, and practices based on the range of threats faced by the Company. There are processes around access management, data security, encryption, asset management, secure system development, security operations, network and device security to provide safeguards from a cybersecurity incident along with continual monitoring of various threat intelligence feeds.
Cyber Risk Management Personnel
The Company's director of cybersecurity reports to the CIO and the CIO reports directly to the Company's chief executive officer. The Company's CIO who served as the first CIO of the Company since 2016, oversaw the information technology and cybersecurity portfolios until her retirement on January 10, 2025. A new CIO from within the Company was named to succeed the retiring CIO and holds both a bachelor's and master's degree in business administration with over 25 years of information technology experience in the energy and utilities business. The director of cybersecurity has a bachelor’s degree in computer information systems, over 25 years of information security experience, and holds certified information systems security professional and certified risk and information systems control certifications. The other members of information technology director level leadership also responsible for managing cybersecurity risks have degrees including Bachelor of Computer Information Systems, information systems management, electronics, electrical engineering, business administration, and accounting, along with certified information systems auditor certification and a cybersecurity fundamentals certificate.
Cyber Risk Oversight Committee
Additionally, in 2014 the board of directors established CyROC to provide executive management and the audit committee of the board of directors with analyses, appraisals, recommendations and pertinent information concerning cyber defense of the Company's electronic information, information technology and operation technology systems. The CyROC is responsible for guiding the Company's comprehensive cybersecurity policies and oversight of cybersecurity risks. The CyROC is chaired by the Company's CIO and is comprised of members such as the chief financial officer, information technology leaders, internal auditors, and other leaders from across the Company.
Cybersecurity Risk Management Positions or Committees Responsible [Flag] true
Cybersecurity Risk Management Positions or Committees Responsible [Text Block] The Company's CIO plays a large role in informing the audit committee of the board of directors on cybersecurity risks. The audit committee of the board of directors receives presentations and reports from the CIO on cybersecurity related issues which include information security, technology risks and risk mitigation programs regularly at the quarterly board meetings.
Cybersecurity Risk Management Expertise of Management Responsible [Text Block] The Company's director of cybersecurity reports to the CIO and the CIO reports directly to the Company's chief executive officer. The Company's CIO who served as the first CIO of the Company since 2016, oversaw the information technology and cybersecurity portfolios until her retirement on January 10, 2025. A new CIO from within the Company was named to succeed the retiring CIO and holds both a bachelor's and master's degree in business administration with over 25 years of information technology experience in the energy and utilities business. The director of cybersecurity has a bachelor’s degree in computer information systems, over 25 years of information security experience, and holds certified information systems security professional and certified risk and information systems control certifications. The other members of information technology director level leadership also responsible for managing cybersecurity risks have degrees including Bachelor of Computer Information Systems, information systems management, electronics, electrical engineering, business administration, and accounting, along with certified information systems auditor certification and a cybersecurity fundamentals certificate.
Cybersecurity Risk Process for Informing Management or Committees Responsible [Text Block]
The Company has an incident response plan to identify, protect, detect, respond to, and recover from cybersecurity threats and incidents that is also tested on an annual basis. The incident response plan is updated based on results of the test or as new cyber related developments occur. The CIO, executive leadership which includes the chief executive officer, chief financial officer, chief accounting officer, chief legal officer, and SEC financial reporting department employees, and the board of directors are notified of any material cybersecurity incidents through a defined escalation process. The defined escalation process is a risk-based process that specifies who is to be contacted and when at each risk level.
Cybersecurity Risk Management Positions or Committees Responsible Report to Board [Flag] true
v3.25.0.1
Significant Accounting Policies (Policies)
 12 Months Ended
Dec. 31, 2024
Accounting Policies [Abstract]  
Basis of presentation
The consolidated financial statements of the Company include the accounts of the following businesses: electric, natural gas distribution, pipeline and other. For further descriptions of the Company's businesses, see Note 17.
On May 31, 2023, the Company completed the separation of Knife River, formerly the construction materials and contracting segment, resulting in Knife River becoming an independent, publicly-traded company. The Company's board of directors approved the distribution of approximately 90 percent of the issued and outstanding shares of Knife River to the Company's stockholders. Stockholders of the Company received one share of Knife River common stock for every four shares of the Company's common stock held on May 22, 2023, the record date for the distribution. The Company retained approximately 10 percent or 5.7 million shares of Knife River common stock immediately following the separation, which were disposed of in a tax-free exchange in November 2023. The separation of Knife River was a tax-free spinoff transaction to the Company's stockholders for U.S. federal income tax purposes, except for cash received in lieu of fractional shares.
On October 31, 2024, the Company completed the separation of Everus, its construction services business, resulting in Everus becoming an independent, publicly-traded company. The Company's board of directors approved the distribution of all the outstanding shares of Everus common stock to the Company's stockholders. Stockholders of the Company received one share of Everus common stock for every four shares of the Company's common stock held as of the close of business on October 21, 2024, the record date for the distribution. The separation of Everus was a tax-free spinoff transaction to the Company's stockholders for U.S. federal income tax purposes, except for cash received in lieu of fractional shares.
The Company's consolidated financial statements and accompanying notes for the current and prior periods have been restated to present the results of operations and the assets and liabilities of Knife River and Everus as discontinued operations, other than certain corporate overhead costs of the Company historically allocated to Knife River and Everus, which are reflected in Other. Also included in discontinued operations in the Consolidated Statements of Income are the supporting activities of Fidelity and certain interest expense related to financing activity associated with the Knife River and Everus separations. The assets and liabilities of the Company's discontinued operations are included in current assets of discontinued operations, noncurrent assets of discontinued operations, current liabilities of discontinued operations and noncurrent liabilities of discontinued operations on the Consolidated Balance Sheets. Unless otherwise indicated, the amounts presented in the accompanying notes to the consolidated financial statements relate to the Company's continuing operations. For more information on discontinued operations, see Note 3.
Additionally, certain amounts recorded in prior year financial statements have been reclassified to conform to the current year presentation. The Company has reclassified $26.9 million and $27.4 million of transmission-related expenses from operation and maintenance to electric fuel and purchased power for the years ended December 31, 2023 and 2022, respectively, in the Consolidated Statements of Income. These transmission-related expenses are an integral component of the cost of electricity sold to customers and therefore, more appropriately reflected in electric fuel and purchased power than operation and maintenance expense. These reclassifications had no effect on previously reported results of operations or cash flows.
Management has also evaluated the impact of events occurring after December 31, 2024, up to the date of issuance of these consolidated financial statements on February 20, 2025, that would require recognition or disclosure in the financial statements.
Principles of consolidation
Principles of consolidation
The consolidated financial statements were prepared in accordance with GAAP and include the accounts of the Company and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation, except for certain transactions related to regulated operations in accordance with GAAP. For more information on intercompany revenues, see Note 17.
The statements also include the Company's ownership interests in the assets, liabilities and expenses of jointly owned electric transmission and generating facilities.
Use of estimates
Use of estimates
The preparation of financial statements in conformity with GAAP requires the Company to make estimates and assumptions that affect the reported amounts of assets and liabilities, and disclosure of contingent assets and liabilities, at the date of the financial statements, as well as the reported amounts of revenues and expenses during the reporting period. Estimates are used for items such as long-lived assets and goodwill; property depreciable lives; tax provisions; revenue recognized using the cost-to-cost measure of progress for contracts; expected credit losses; environmental and other loss contingencies; regulatory assets expected to be recovered in rates charged to customers; costs on construction contracts; unbilled revenues; actuarially determined benefit costs; asset retirement obligations; lease classification; present value of right-of-use assets and lease liabilities; and the valuation of stock-based compensation. As additional information becomes available, or actual amounts are determinable, the recorded estimates are revised. Consequently, operating results can be affected by revisions to prior accounting estimates.
New accounting standards
New accounting standards
The following table provides a brief description of the accounting pronouncements applicable to the Company and the potential impact on its financial statements and/or disclosures:
StandardDescriptionEffective dateImpact on financial statements/disclosures
Recently adopted accounting standards
ASU 2022-06 - Reference Rate Reform: Deferral of Sunset DateIn December 2022, the FASB included a sunset provision within ASC 848 based on expectations of when LIBOR would cease being published. At the time ASU 2020-04 was issued, the UK Financial Conduct Authority had established its intent to cease overnight tenors of LIBOR after December 31, 2021. In March 2021, the UK Financial Conduct Authority announced that the intended cessation date of the overnight tenors of LIBOR would be June 30, 2023 which is beyond the current sunset date of ASC 848. The amendments in this Update defer the sunset date of ASC 848 from December 31, 2022 to December 31, 2024, after which entities will no longer be permitted to apply the relief in ASC 848.December 31, 2024
The Company has updated its credit agreements to include language regarding the successor or alternate rate to LIBOR. The Company did not have a material impact on its results of operations, financial position, cash flows or disclosures.
ASU 2023-07 Segment Reporting - Improvements to Reportable Segment Disclosures
In November 2023, the FASB issued guidance on improving financial reporting by requiring disclosure of incremental segment information, primarily through enhanced disclosures about significant segment expenses, on an annual and interim basis for all public entities to enable investors to develop more decision-useful financial analyses.
December 31, 2024
The Company identified and updated disclosures to ensure compliance with the new guidance. See Note 17.
Recently issued accounting standards not yet adopted
ASU 2023-09 Income Taxes - Improvements to Income Tax Disclosures an Amendment, December 2023
In December 2023, the FASB issued guidance to address investors requests for more transparency about income tax information through improvements to income tax disclosures primarily related to the rate reconciliation and income taxes paid information and effectiveness of income tax disclosures.
Effective for annual reporting periods beginning after 2024 on a prospective basis.
The Company is currently evaluating the impact the guidance will have on its disclosures for the year ended December 31, 2025.
ASU 2024-01 Compensation - Stock Compensation
In March 2024, the FASB issued Improvements to GAAP through an example to demonstrate application of the scope of paragraph 718-10-15-3 to determine whether profits interest and similar awards should be accounted in Compensation - Stock Compensation.
Effective for fiscal year beginning after December 15, 2024.The Company is currently evaluating the impact the guidance will have on its disclosures for the year ended December 31, 2025.
ASU 2024-03 Disaggregation of Income Statement Expenses
In November 2024, the FASB issued guidance to improve the disclosures about a public business entity's expenses and address requests from investors for more detailed information about the types of expenses (including purchases of inventory, employee compensation, depreciation, amortization, and depletion) in commonly presented expense captions (such as cost of sales, selling, general, and administrative; and research and development).
Effective for annual reporting periods beginning after December 15, 2026, and interim reporting periods beginning after December 15, 2027.
The Company is currently evaluating the impact the guidance will have on its disclosures for the year ended December 31, 2027.
Cash, cash equivalents and restricted cash
Cash, cash equivalents and restricted cash
The Company considers all highly liquid investments purchased with an original maturity of three months or less to be cash equivalents. Restricted cash represents deposits held by the Company’s captive insurance company that is required by state insurance regulations to remain in the captive insurance company.
Revenue recognition
Revenue recognition
Revenue is recognized when a performance obligation is satisfied by transferring control over a product or service to a customer. Revenue is measured based on consideration specified in a contract with a customer and excludes any sales incentives and amounts collected on behalf of third parties. The Company is considered an agent for certain taxes collected from customers. As such, the Company presents revenues net of these taxes at the time of sale to be remitted to governmental authorities, including sales and use taxes.
The electric and natural gas distribution segments generate revenue from the sales of electric and natural gas products and services, which includes retail and transportation services. These segments establish a customer's retail or transportation service account based on the customer's application/contract for service, which indicates approval of a contract for service. The contract identifies an obligation to provide service in exchange for delivering or standing ready to deliver the identified commodity; and the customer is obligated to pay for the service as provided in the applicable tariff. The product sales are based on a fixed rate that includes a base and per-unit rate, which are included in approved tariffs as determined by state or federal regulatory agencies. The quantity of the commodity consumed or transported determines the total per-unit revenue. The service provided, along with the product consumed or transported, are a single performance obligation because both are required in combination to successfully transfer the contracted product or service to the customer. Revenues are recognized over time as customers receive and consume the products and services. The method of measuring progress toward the completion of the single performance obligation is on a per-unit output method basis, with revenue recognized based on the direct measurement of the value to the customer of the goods or services transferred to date. For contracts governed by the Company’s utility tariffs, amounts are billed monthly with the amount due between 15 and 22 days of receipt of the invoice depending on the applicable state’s tariff. For other contracts not governed by tariff, payment terms are net 30 days. At this time, the segment has no material obligations for returns, refunds or other similar obligations.
The pipeline segment generates revenue from providing natural gas transportation and underground storage services, as well as other energy-related services to both third parties and internal customers, largely the natural gas distribution segment. The pipeline segment establishes a contract with a customer based upon the customer’s request for firm or interruptible natural gas transportation or storage service(s). The contract identifies an obligation for the segment to provide the requested service(s) in exchange for consideration from the customer over a specified term. Depending on the type of service(s) requested and contracted, the service provided may include transporting or storing an identified quantity of natural gas and/or standing ready to deliver or store an identified quantity of natural gas. Natural gas transportation and storage revenues are based on fixed rates, which may include reservation fees and/or per-unit commodity rates. The services provided by the segment are generally treated as single performance obligations satisfied over time simultaneous to when the service is provided and revenue is recognized. Rates for the segment’s regulated services are based on its FERC approved tariff or customer negotiated rates, and rates for its non-regulated services are negotiated with its customers and set forth in the contract. For contracts governed by the company’s tariff, amounts are billed on or before the ninth business day of the following month and the amount is due within 12 days of receipt of the invoice. For other contracts not governed by the tariff, payment terms are net 30 days. At this time, the segment has no material obligations for returns, refunds or other similar obligations.
The Company recognizes all other revenues when services are rendered or goods are delivered.
Legal costs
Legal costs
The Company generally expenses external legal fees as they are incurred unless it has specific circumstances to defer, such as probable recovery in a rate proceeding.
Receivables and allowance for expected credit losses Receivables consist primarily of trade receivables from the sale of goods and services net of expected credit losses. The Company's trade receivables are all due in 12 months or less.The Company's expected credit losses are determined through a review using historical credit loss experience, changes in asset specific characteristics, current conditions and reasonable and supportable future forecasts, among other specific account data, and is performed at least quarterly. The Company develops and documents its methodology to determine its allowance for expected credit losses at each of its reportable business segments. Risk characteristics used by the business segments may include customer mix, knowledge of customers and general economic conditions of the various local economies, among others. Specific account balances are written off when management determines the amounts to be uncollectible. Management has reviewed the balance reserved through the allowance for expected credit losses and believes it is reasonable.
Inventories and natural gas in storage
Inventories and natural gas in storage            
Natural gas in storage is generally valued at lower of cost or market using the last-in, first-out method or lower of cost or net realizable value using the average cost or first-in, first-out method. The majority of all other inventories are valued at the lower of cost or net realizable value using the average cost method.
Property, plant and equipment
Property, plant and equipment
Additions to property, plant and equipment are recorded at cost. When regulated assets are retired, or otherwise disposed of in the ordinary course of business, the original cost of the asset is charged to accumulated depreciation. With respect to the retirement or disposal of all other assets, the resulting gains or losses are recognized as a component of income.
The Company is permitted to capitalize AFUDC on regulated construction projects and to include such amounts in rate base when the related facilities are placed in service. In addition, the Company capitalizes interest, when applicable, on certain contracting services projects associated with its other operations.
Impairment of long-lived assets, excluding goodwill
Impairment of long-lived assets, excluding goodwill
The Company reviews the carrying values of its long-lived assets, whenever events or changes in circumstances indicate that such carrying values may not be recoverable. The Company tests long-lived assets for impairment at a level significantly lower than that of goodwill impairment testing. Long-lived assets or groups of assets that are evaluated for impairment at the lowest level of largely independent identifiable cash flows at an individual operation or group of operations collectively serving a local market. The determination of whether an impairment has occurred is based on an estimate of undiscounted future cash flows attributable to the assets, compared to the carrying value of the assets. If impairment has occurred, the amount of the impairment recognized is determined by estimating the fair value of the assets and recording a loss if the carrying value is greater than the fair value.
Regulatory assets and liabilities
Regulatory assets and liabilities
The Company is subject to various state and federal agency regulations. The accounting policies followed by the Company are generally subject to the Uniform System of Accounts of the FERC as well as the provisions of ASC 980 - Regulated Operations. These accounting policies differ in some respects from those used by the Company's non-regulated businesses.
The Company accounts for certain income and expense items under the provisions of regulatory accounting, which requires the Company to defer as regulatory assets or liabilities certain items that would have otherwise been reflected as expense or income, respectively. The Company records regulatory assets or liabilities at the time the Company determines the amounts to be recoverable in current or future rates. Regulatory assets and liabilities are being amortized consistently with the regulatory treatment established by the FERC and the applicable state public service commission. See Note 6 for more information regarding the nature and amounts of these regulatory deferrals.
Goodwill
Goodwill
Goodwill represents the excess of the purchase price over the fair value of identifiable net tangible and intangible assets acquired in a business combination. Goodwill is required to be tested for impairment annually, which the Company completes in the fourth quarter, or more frequently if events or changes in circumstances indicate that goodwill may be impaired.
The Company has determined that the reporting units for its goodwill impairment test are its operating segments, or components of an operating segment, that constitute a business for which discrete financial information is available and for which segment management regularly reviews the operating results. As of December 31, 2024, the only operating segment with goodwill was the natural gas distribution segment. For more information on the Company's operating segments, see Note 17.
Goodwill impairment, if any, is measured by comparing the fair value of each reporting unit to its carrying value. If the fair value of a reporting unit exceeds its carrying value, the goodwill of the reporting unit is not impaired. If the carrying value of a reporting unit exceeds its fair value, the Company must record an impairment loss for the amount that the carrying value of the reporting unit, including goodwill, exceeds the fair value of the reporting unit.
Investments
Investments
The Company's investments include the cash surrender value of life insurance policies, insurance contracts, mortgage-backed securities and U.S. Treasury securities. The Company measures its investment in the insurance contracts at fair value with any unrealized gains and losses recorded on the Consolidated Statements of Income. The Company has not elected the fair value option for its mortgage-backed securities and U.S. Treasury securities and, as a result, the unrealized gains and losses on these investments are recorded in accumulated other comprehensive loss. For more information, see Notes 9 and 18.
Variable interest entities
Variable interest entities
The Company evaluates its arrangements and contracts with other entities to determine if they are VIEs and if so, if the Company is the primary beneficiary. GAAP provides a framework for identifying VIEs and determining when a company should include the assets, liabilities, noncontrolling interest and results of activities of a VIE in its consolidated financial statements.
A VIE should be consolidated if a party with an ownership, contractual or other financial interest in the VIE (a variable interest holder) has the power to direct the VIE's most significant activities and the obligation to absorb losses or right to receive benefits of the VIE that could be significant to the VIE. A variable interest holder that consolidates the VIE is called the primary beneficiary. Upon consolidation, the primary beneficiary generally must initially record all of the VIE's assets, liabilities and noncontrolling interests at fair value and subsequently account for the VIE as if it were consolidated.
The Company's evaluation of whether it qualifies as the primary beneficiary of a VIE involves significant judgments, estimates and assumptions and includes a qualitative analysis of the activities that most significantly impact the VIE's economic performance and whether the Company has the power to direct those activities, the design of the entity, the rights of the parties and the purpose of the arrangement.
Derivative instruments
Derivative instruments
The Company enters into commodity price derivative contracts in order to minimize the price volatility associated with customer natural gas costs at its natural gas distribution segment. These derivatives are not designated as hedging instruments and are recorded in the Consolidated Balance Sheets at fair value. Changes in the fair value of these derivatives along with any contract settlements are recorded each period in regulatory assets or liabilities in accordance with regulatory accounting. The Company does not enter into any derivatives for trading or other speculative purposes.
Leases
Leases
Lease liabilities and their corresponding right-of-use assets are recorded based on the present value of lease payments over the expected lease term. The Company recognizes leases with an original lease term of 12 months or less in income on a straight-line basis over the term of the lease and does not recognize a corresponding right-of-use asset or lease liability. The Company determines the lease term based on the non-cancelable and cancelable periods in each contract. The non-cancelable period consists of the term of the contract that is legally enforceable and cannot be canceled by either party without incurring a significant penalty. The cancelable period is determined by various factors that are based on who has the right to cancel a contract. If only the lessor has the right to cancel the contract, the Company will assume the contract will continue. If the lessee is the only party that has the right to cancel the contract, the Company looks to asset, entity and market-based factors. If both the lessor and the lessee have the right to cancel the contract, the Company assumes the contract will not continue.
The discount rate used to calculate the present value of the lease liabilities is based upon the implied rate within each contract. If the rate is unknown or cannot be determined, the Company uses an incremental borrowing rate, which is determined by the length of the contract, asset class and the Company's borrowing rates, as of the commencement date of the contract.
Asset retirement obligations
Asset retirement obligations
The Company records the fair value of a liability for an asset retirement obligation in the period in which it is incurred. When the liability is initially recorded, the Company capitalizes a cost by increasing the carrying amount of the related long-lived asset. Over time, the liability is accreted to its present value each period and the capitalized cost is depreciated over the useful life of the related asset. Upon settlement of the liability, the Company either settles the obligation for the recorded amount or incurs a gain or loss at its non-regulated operations or incurs a regulatory asset or liability at its regulated operations.
Stock-based compensation
Stock-based compensation
The Company determines compensation expense for stock-based awards based on the estimated fair values at the grant date and recognizes the related compensation expense over the vesting period. The Company uses the straight-line amortization method to recognize compensation expense related to RSUs, which only has a service condition. This method recognizes stock compensation expense on a straight-line basis over the requisite service period for the entire award. The Company recognized compensation expense related to PSAs that vest based on performance metrics and service conditions on a straight-line basis over the service period. Inception-to-date expense was adjusted based upon the determination of the potential achievement of the performance target at each reporting date. The Company recognized compensation expense related to PSAs with market-based performance metrics on a straight-line basis over the requisite service period. Outstanding PSAs were converted to RSUs in connection with the completed separation of Knife River through the spinoff.
The Company records the compensation expense for PSAs using an estimated forfeiture rate. The estimated forfeiture rate is calculated based on an average of actual historical forfeitures. The Company also performs an analysis of any known factors at the time of the calculation to identify any necessary adjustments to the average historical forfeiture rate. At the time actual forfeitures become more than estimated forfeitures, the Company records compensation expense using actual forfeitures.
Earnings per share Basic earnings per share is computed by dividing net income by the weighted average number of shares of common stock outstanding during the year. Diluted earnings per share is computed by dividing net income by the total of the weighted average number of shares of common stock outstanding during the year, plus the effect of nonvested performance share awards and restricted stock units.
Income taxes
Income taxes
The Company provides deferred federal and state income taxes on all temporary differences between the book and tax basis of the Company's assets and liabilities by using enacted tax rates in effect for the year in which the differences are expected to reverse. The effect of a change in tax rates on deferred tax assets and liabilities is recognized in income in the period that includes the enactment date. Excess deferred income tax balances associated with the Company's rate-regulated activities have been recorded as regulatory liabilities. These regulatory liabilities are expected to be reflected as a reduction in future rates charged to customers in accordance with applicable regulatory procedures.
The Company uses the deferral method of accounting for investment tax credits and amortizes the credits on regulated electric and natural gas distribution plant over various periods that conform to the ratemaking treatment prescribed by the applicable state public service commissions.
Income taxes, uncertainties The Company records uncertain tax positions in accordance with accounting guidance on accounting for income taxes on the basis of a two-step process in which (1) the Company determines whether it is more-likely-than-not that the tax position will be sustained on the basis of the technical merits of the position and (2) for those tax positions that meet the more-likely-than-not recognition threshold, the Company recognizes the largest amount of the tax benefit that is more than 50 percent likely to be realized upon ultimate settlement with the related tax authority. Tax positions that do not meet the more-likely-than-not criteria are reflected as a tax liability. The Company recognizes interest and penalties accrued related to unrecognized tax benefits in income taxes.
Discontinued Operations
As a result of the separations, the historical results of operations are shown in discontinued operations, net of tax, except for allocated general corporate overhead costs of the Company, which did not meet the criteria for discontinued operations. The Company’s consolidated financial statements and accompanying notes for prior periods have been restated. For the comparative periods, Everus' operations are only reflected through October 2024 compared to the full year in 2023 and 2022 and Knife River's operations are only reflected through May 2023 compared to the full year in 2022.
Revenue from Contracts with Customers
Revenue is recognized when a performance obligation is satisfied by transferring control over a product or service to a customer. Revenue is measured based on consideration specified in a contract with a customer and excludes any sales incentives and amounts collected on behalf of third parties. The Company is considered an agent for certain taxes collected from customers. As such, the Company presents revenues net of these taxes at the time of sale to be remitted to governmental authorities, including sales and use taxes.
As part of the adoption of ASC 606 - Revenue from Contracts with Customers, the Company elected the practical expedient to recognize the incremental costs of obtaining a contract as an expense when incurred if the amortization period of the asset that the Company otherwise would have recognized is 12 months or less.
Environmental Allowances and Obligations Environmental Allowances and Obligations
Beginning in 2023, the Company's natural gas distribution segment acquires environmental allowances as part of its requirement to comply with environmental regulations in certain states. Allowances are allocated by the respective states to the Company at no cost and additional allowances are required to be purchased as needed based on the requirements in the respective states. The segment records purchased and allocated environmental allowances at weighted average cost under the inventory method of accounting. Environmental allowances are included in Prepayments and other current assets and noncurrent assets - Other on the Consolidated Balance Sheets.
Environmental compliance obligations, which are based on GHG emissions, are measured at the carrying value of environmental allowances held plus the estimated value of additional allowances necessary to satisfy the compliance obligation. Environmental compliance obligations are included in current liabilities - Other accrued liabilities and noncurrent liabilities - Other on the Consolidated Balance Sheets.
The Company recognizes revenue from the sale of emissions allowances allocated under the environmental programs when the allowances are sold at auction. The revenues associated with the sale of these allowances are deferred as a component of the respective jurisdiction’s regulatory liability for environmental compliance.
As environmental allowances are surrendered, the segment reduces the associated environmental compliance assets and liabilities from the Consolidated Balance Sheets. The expenses and revenues associated with the Company’s environmental allowances and obligations are deferred as regulatory assets and liabilities and recognized as a component of purchased natural gas sold as recovered in customer rates. For more information on the Company’s regulatory assets and liabilities, see Note 6.
Accumulated Other Comprehensive Loss The Company's accumulated other comprehensive loss is comprised of losses on derivative instruments qualifying as hedges, postretirement liability adjustments and gain (loss) on available-for-sale investments.
Business Segment Data The Company's reportable segments are those that are based on the Company's method of internal reporting, which generally segregates the strategic business activities due to differences in products, services and regulation. The internal reporting of these operating segments is defined based on the reporting and review process used by the Company's CODM, the chief executive officer.
Commitments and Contingencies
The Company is party to claims and lawsuits arising out of its business and that of its consolidated subsidiaries, which may include, but are not limited to, matters involving property damage, personal injury, and environmental, contractual, statutory and regulatory obligations. The Company accrues a liability for those contingencies when the incurrence of a loss is probable and the amount can be reasonably estimated. If a range of amounts can be reasonably estimated and no amount within the range is a better estimate than any other amount, then the minimum of the range is accrued. The Company does not accrue liabilities when the likelihood that the liability has been incurred is probable but the amount cannot be reasonably estimated or when the liability is believed to be only reasonably possible or remote. For contingencies where an unfavorable outcome is probable or reasonably possible and which are material, the Company discloses the nature of the contingency and, in some circumstances, an estimate of the possible loss. Accruals are based on the best information available, but in certain situations management is unable to estimate an amount or range of a reasonably possible loss including, but not limited to when: (1) the damages are unsubstantiated or indeterminate, (2) the proceedings are in the early stages, (3) numerous parties are involved, or (4) the matter involves novel or unsettled legal theories.
v3.25.0.1
Significant Accounting Policies (Tables)
 12 Months Ended
Dec. 31, 2024
Accounting Policies [Abstract]  
Schedule of Expected Credit Loss
Details of the Company's expected credit losses were as follows:
ElectricNatural gas
distribution		PipelineTotal
 (In thousands)
At December 31, 2022
$375 $1,615 $2 $1,992 
Current expected credit loss provision
1,645 5,777 — 7,422 
Less write-offs charged against the allowance1,994 7,355 2 9,351 
Credit loss recoveries collected388 1,152 — 1,540 
At December 31, 2023414 1,189 — 1,603 
Current expected credit loss provision1,891 4,667 — 6,558 
Less write-offs charged against the allowance2,218 5,709 — 7,927 
Credit loss recoveries collected386 1,219 — 1,605 
At December 31, 2024$473 $1,366 $— $1,839 
Schedule of Inventory Inventories at December 31 consisted of:
 20242023
 (In thousands)
Natural gas in storage (current)$40,073 $39,377 
Fuel stock4,867 5,307 
Total$44,940 $44,684 
Schedule of Property, Plant and Equipment The amount of AFUDC for the years ended December 31 was as follows:
202420232022
(In thousands)
AFUDC - borrowed$10,964 $10,035 $2,236 
AFUDC - equity$2,251 $1,894 $2,165 
Schedule of Earnings Per Share Reconciliation A reconciliation of the weighted average common shares outstanding used in the basic and diluted earnings per share calculations follows:
2024 2023 2022 
(In thousands, except per share amounts)
Weighted average common shares outstanding - basic203,867 203,640 203,358 
Effect of dilutive performance share awards786 298 104 
Weighted average common shares outstanding - diluted204,653 203,938 203,462 
Earnings per share - basic:
Income from continuing operations
$.89 $1.62 $.58 
Discontinued operations, net of tax
.49 .42 1.23 
Earnings per share - basic
$1.38 $2.04 $1.81 
Earnings per share - diluted:
Income from continuing operations
$.88 $1.62 $.58 
Discontinued operations, net of tax
.49 .41 1.23 
Earnings per share - diluted
$1.37 $2.03 $1.81 
Shares excluded from the calculation of diluted earnings per share— — 14 
Dividends declared per common share
$.5100 $.6950 $.8750 
v3.25.0.1
Discontinued Operations (Tables)
 12 Months Ended
Dec. 31, 2024
Discontinued Operations and Disposal Groups [Abstract]  
Schedule of Disposal Groups, Including Discontinued Operations The carrying amounts of the major classes of assets and liabilities related to the discontinued operations of Everus included in the Company’s Consolidated Balance Sheet at December 31, 2023 were as follows:
December 31, 2023
Assets(In Thousands)
Current assets:
Cash and cash equivalents$16,501 
Receivables, net692,629 
Inventories42,709 
Prepayments and other current assets17,651 
Total current assets of discontinued operations769,490 
Noncurrent assets:
Net property, plant and equipment116,018 
Goodwill143,224 
Other intangible assets, net2,004 
Investments11,760 
Operating lease right-of-use assets53,232 
Other21,627 
Total noncurrent assets of discontinued operations347,865 
Total assets of discontinued operations$1,117,355 
Liabilities
Current liabilities:
Accounts payable$315,240 
Taxes payable8,557 
Accrued compensation44,721 
Operating lease liabilities due within one year21,143 
Other accrued liabilities53,619 
Total current liabilities of discontinued operations443,280 
Noncurrent liabilities:
Long-term debt132,000 
Deferred income taxes6,212 
Operating lease liabilities32,504 
Other8,934 
Total noncurrent liabilities of discontinued operations179,650 
Total liabilities of discontinued operations$622,930 
The reconciliation of the major classes of income and expense constituting pretax income from discontinued operations to the after-tax income from discontinued operations on the Consolidated Statements of Income were as follows:
202420232022
(In thousands)
Operating revenues$2,377,332 $3,589,251 $5,226,766 
Operating expenses2,241,162 3,422,393 4,853,408 
Operating (loss) income
136,170 166,858 373,358 
Other income (expense)12,446 10,599 4,119 
Interest expense7,118 47,229 38,590 
Income from discontinued operations before income taxes
141,498 130,228 338,887 
Income taxes41,463 45,638 88,650 
Discontinued operations, net of tax$100,035 $84,590 $250,237 
v3.25.0.1
Revenue from Contracts with Customers (Tables)
 12 Months Ended
Dec. 31, 2024
Revenue from Contract with Customer [Abstract]  
Schedule of Disaggregation of Revenue
Disaggregation
In the following table, revenue is disaggregated by the type of customer or service provided. The Company believes this level of disaggregation best depicts how the nature, amount, timing and uncertainty of revenue and cash flows are affected by economic factors. The table also includes a reconciliation of the disaggregated revenue by reportable segments. For more information on the Company's business segments, see Note 17.
Year ended December 31, 2024ElectricNatural gas distributionPipelineOtherTotal
(In thousands)
Residential utility sales
$140,054 $646,049 $— $— $786,103 
Commercial utility sales171,760 399,087 — — 570,847 
Industrial utility sales42,883 42,588 — — 85,471 
Other utility sales7,910 — — — 7,910 
Natural gas transportation— 60,645 174,623 — 235,268 
Natural gas storage— — 23,690 — 23,690 
Other59,288 40,703 13,139 195 113,325 
Intersegment eliminations(72)(130)(69,222)(195)(69,619)
Revenues from contracts with customers421,823 1,188,942 142,230 — 1,752,995 
Other revenues(7,417)12,033 367 — 4,983 
Total external operating revenues$414,406 $1,200,975 $142,597 $— $1,757,978 

Year ended December 31, 2023ElectricNatural gas distributionPipelineOtherTotal
(In thousands)
Residential utility sales$136,274 $724,600 $— $— $860,874 
Commercial utility sales170,321 442,507 — — 612,828 
Industrial utility sales43,063 45,205 — — 88,268 
Other utility sales7,270 — — — 7,270 
Natural gas transportation— 52,465 145,297 — 197,762 
Natural gas storage— — 18,254 — 18,254 
Other54,508 15,141 13,874 119 83,642 
Intersegment eliminations(138)(301)(62,533)(119)(63,091)
Revenues from contracts with customers411,298 1,279,617 114,892 — 1,805,807 
Other revenues(10,261)7,619 187 — (2,455)
Total external operating revenues$401,037 $1,287,236 $115,079 $— $1,803,352 
Year ended December 31, 2022ElectricNatural gas distributionPipelineOtherTotal
(In thousands)
Residential utility sales$138,634 $718,191 $— $— $856,825 
Commercial utility sales146,182 453,802 — — 599,984 
Industrial utility sales43,766 41,710 — — 85,476 
Other utility sales7,597 — — — 7,597 
Natural gas transportation— 48,886 129,290 — 178,176 
Natural gas storage— — 14,583 — 14,583 
Other45,608 13,617 11,450 86 70,761 
Intersegment eliminations(58)(216)(58,884)(86)(59,244)
Revenues from contracts with customers381,729 1,275,990 96,439 — 1,754,158 
Other revenues(4,714)(2,402)256 — (6,860)
Total external operating revenues$377,015 $1,273,588 $96,695 $— $1,747,298 
v3.25.0.1
Property, Plant and Equipment (Tables)
 12 Months Ended
Dec. 31, 2024
Property, Plant and Equipment [Abstract]  
Schedule of Property, Plant and Equipment
Property, plant and equipment at December 31 was as follows:
20242023Weighted
Average
Depreciable
Life in Years
(Dollars in thousands, where applicable)
Electric:
Generation$1,014,906 $939,474 49
Distribution546,121 521,215 47
Transmission662,466 639,999 65
CWIP
81,316 115,103 0
Other176,007 153,248 15
Natural gas distribution:
Distribution2,955,435 2,771,540 53
Transmission146,710 115,057 56
Storage43,700 42,654 37
General229,034 215,572 13
CWIP
74,207 70,373 0
Other282,007 246,991 15
Pipeline:
Transmission1,173,259 1,035,995 46
Storage61,369 57,160 53
CWIP
29,629 57,038 0
Other73,749 68,194 17
Other:
Land and other
4,148 31,654 7
Less accumulated depreciation and amortization
2,209,771 2,076,375 
Net property, plant and equipment$5,344,292 $5,004,892 
v3.25.0.1
Regulatory Assets and Liabilities (Tables)
 12 Months Ended
Dec. 31, 2024
Regulatory Assets and Liabilities Disclosure [Abstract]  
Schedule of Regulatory Assets
The following table summarizes the individual components of unamortized regulatory assets and liabilities as of December 31:
Estimated Recovery or Refund Period*2024 2023 
(In thousands)
Regulatory assets:
Current:
Natural gas costs recoverable through rate adjustments
Up to 1 year
$91,091 $98,844 
Environmental compliance programs
Up to 1 year
76,964 5,525 
Conservation programs
Up to 1 year
19,123 14,425 
Electric fuel and purchased power deferral
Up to 1 year
9,662 33,918 
Decoupling mechanisms
Up to 1 year
6,767 — 
Cost recovery mechanisms
Up to 1 year
5,114 9,153 
Other
Up to 1 year
6,715 10,627 
215,436 172,492 
Noncurrent:
Pension and postretirement benefits**142,064 142,511 
Cost recovery mechanisms
Up to 24 years
76,542 85,944 
Plant costs/asset retirement obligationsOver plant lives47,042 46,009 
Manufactured gas plant site remediation-27,964 26,127 
Taxes recoverable from customersOver plant lives12,221 12,249 
Electric fuel and purchased power deferral
Up to 2 years
4,349 — 
Covid-19 deferred costs-4,167 2,746 
Long-term debt refinancing costs
Up to 36 years
2,011 2,600 
Environmental compliance programs-— 66,806 
Natural gas costs recoverable through rate adjustments
Up to 2 years
— 55,493 
Other
Up to 14 years
5,990 6,614 
322,350 447,099 
Total regulatory assets$537,786 $619,591 
Regulatory liabilities:
Current:
Environmental compliance
Up to 1 year
$72,387 $— 
Natural gas costs refundable through rate adjustments
Up to 1 year
45,427 43,161 
Margin sharing
Up to 1 year
4,156 5,243 
Provision for rate refund
Up to 1 year
3,677 6,866 
Taxes refundable to customers
Up to 1 year
2,163 2,149 
Conservation programs
Up to 1 year
2,082 2,130 
Cost recovery mechanisms
Up to 1 year
1,720 6,284 
Other
Up to 1 year
5,555 4,928 
137,167 70,761 
Noncurrent:
Plant removal and decommissioning costsOver plant lives217,603 220,147 
Taxes refundable to customersOver plant lives185,402 193,578 
Cost recovery mechanisms
Up to 17 years
30,354 21,791 
Accumulated deferred investment tax creditOver plant lives18,788 15,740 
Pension and postretirement benefits**4,862 6,044 
Environmental compliance programs-— 61,941 
Other
Up to 13 years
2,161 1,809 
459,170 521,050 
Total regulatory liabilities$596,337 $591,811 
Net regulatory position$(58,551)$27,780 
*Estimated recovery or refund period for amounts currently being recovered or refunded in rates to customers.
**    Recovered as expense is incurred or cash contributions are made.
Schedule of Regulatory Liabilities
The following table summarizes the individual components of unamortized regulatory assets and liabilities as of December 31:
Estimated Recovery or Refund Period*2024 2023 
(In thousands)
Regulatory assets:
Current:
Natural gas costs recoverable through rate adjustments
Up to 1 year
$91,091 $98,844 
Environmental compliance programs
Up to 1 year
76,964 5,525 
Conservation programs
Up to 1 year
19,123 14,425 
Electric fuel and purchased power deferral
Up to 1 year
9,662 33,918 
Decoupling mechanisms
Up to 1 year
6,767 — 
Cost recovery mechanisms
Up to 1 year
5,114 9,153 
Other
Up to 1 year
6,715 10,627 
215,436 172,492 
Noncurrent:
Pension and postretirement benefits**142,064 142,511 
Cost recovery mechanisms
Up to 24 years
76,542 85,944 
Plant costs/asset retirement obligationsOver plant lives47,042 46,009 
Manufactured gas plant site remediation-27,964 26,127 
Taxes recoverable from customersOver plant lives12,221 12,249 
Electric fuel and purchased power deferral
Up to 2 years
4,349 — 
Covid-19 deferred costs-4,167 2,746 
Long-term debt refinancing costs
Up to 36 years
2,011 2,600 
Environmental compliance programs-— 66,806 
Natural gas costs recoverable through rate adjustments
Up to 2 years
— 55,493 
Other
Up to 14 years
5,990 6,614 
322,350 447,099 
Total regulatory assets$537,786 $619,591 
Regulatory liabilities:
Current:
Environmental compliance
Up to 1 year
$72,387 $— 
Natural gas costs refundable through rate adjustments
Up to 1 year
45,427 43,161 
Margin sharing
Up to 1 year
4,156 5,243 
Provision for rate refund
Up to 1 year
3,677 6,866 
Taxes refundable to customers
Up to 1 year
2,163 2,149 
Conservation programs
Up to 1 year
2,082 2,130 
Cost recovery mechanisms
Up to 1 year
1,720 6,284 
Other
Up to 1 year
5,555 4,928 
137,167 70,761 
Noncurrent:
Plant removal and decommissioning costsOver plant lives217,603 220,147 
Taxes refundable to customersOver plant lives185,402 193,578 
Cost recovery mechanisms
Up to 17 years
30,354 21,791 
Accumulated deferred investment tax creditOver plant lives18,788 15,740 
Pension and postretirement benefits**4,862 6,044 
Environmental compliance programs-— 61,941 
Other
Up to 13 years
2,161 1,809 
459,170 521,050 
Total regulatory liabilities$596,337 $591,811 
Net regulatory position$(58,551)$27,780 
*Estimated recovery or refund period for amounts currently being recovered or refunded in rates to customers.
**    Recovered as expense is incurred or cash contributions are made.
v3.25.0.1
Fair Value Measurements (Tables)
 12 Months Ended
Dec. 31, 2024
Fair Value Disclosures [Abstract]  
Schedule of Debt Securities, Available-for-sale Details of available-for-sale securities were as follows:
December 31, 2024CostGross
Unrealized
Gains		Gross
Unrealized
Losses		Fair Value
(In thousands)
Mortgage-backed securities$7,933 $4 $383 $7,554 
U.S. Treasury securities3,945 80 1 4,024 
Total$11,878 $84 $384 $11,578 
December 31, 2023CostGross
Unrealized
Gains		Gross
Unrealized
Losses		Fair Value
(In thousands)
Mortgage-backed securities$8,234 $17 $470 $7,781 
U.S. Treasury securities3,521 28 8 3,541 
Total$11,755 $45 $478 $11,322 
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis
The Company's assets measured at fair value on a recurring basis were as follows:
 
Fair Value Measurements at December 31, 2024, Using
 
 Quoted Prices
in Active
Markets for
Identical
Assets
(Level 1)		Significant
Other
Observable
Inputs
(Level 2)		Significant
Unobservable
Inputs
 (Level 3)		Balance at December 31, 2024
 (In thousands)
Assets:    
Money market funds$— $12,879 $— $12,879 
Insurance contracts*— 59,282 — 59,282 
Available-for-sale securities:
Mortgage-backed securities— 7,554 — 7,554 
U.S. Treasury securities— 4,024 — 4,024 
Total assets measured at fair value$— $83,739 $— $83,739 
*The insurance contracts invest approximately 58 percent in fixed-income investments, 17 percent in common stock of large-cap companies, 8 percent in target date investments, 8 percent in common stock of mid-cap companies, 4 percent in common stock of small-cap companies, 4 percent in cash equivalents, and 1 percent in international investments.
 
Fair Value Measurements at December 31, 2023, Using
 
 Quoted Prices
in Active
Markets for
Identical
Assets
 (Level 1)		Significant
Other
Observable
Inputs
(Level 2)		Significant
Unobservable
Inputs
 (Level 3)		Balance at December 31, 2023
 (In thousands)
Assets:    
Money market funds$— $6,409 $— $6,409 
Insurance contracts*— 62,936 — 62,936 
Available-for-sale securities:
Mortgage-backed securities— 7,781 — 7,781 
U.S. Treasury securities— 3,541 — 3,541 
Total assets measured at fair value$— $80,667 $— $80,667 
*The insurance contracts invest approximately 60 percent in fixed-income investments, 15 percent in common stock of large-cap companies, 8 percent in target date investments, 7 percent in common stock of mid-cap companies, 5 percent in common stock of small-cap companies, 3 percent in cash equivalents, 1 percent in high yield investments, and 1 percent in international investments.
Schedule of Fair Value, by Balance Sheet Grouping The estimated fair value of the Company's Level 2 long-term debt at December 31 was as follows:
 20242023
 (In thousands)
Carrying Amount$2,292,610 $2,166,223 
Fair Value$1,963,396 $1,914,039 
v3.25.0.1
Debt (Tables)
 12 Months Ended
Dec. 31, 2024
Debt Disclosure [Abstract]  
Schedule of Line of Credit Facilities
The following table summarizes the outstanding revolving credit facilities of the Company and its subsidiaries:
CompanyFacilityFacility
Limit		 
Amount Outstanding at December 31, 2024
Amount Outstanding at December 31, 2023
Letters of
Credit at December 31, 2024
Expiration
Date
  (In millions)
Montana-Dakota Utilities Co.Commercial paper/Revolving credit agreement (a)$200.0  $81.4 $144.2 $— 10/18/28
Cascade Natural Gas Corporation
Revolving credit agreement
$175.0 (b)$64.6 $15.4 $2.2 (c)6/20/29
Intermountain Gas Company
Revolving credit agreement
$175.0 
(b)
$105.1 $30.7 $— 6/20/29
MDU Resources Group, Inc.
Revolving credit agreement
$200.0 
(d)
$— $— $12.1 (c)5/31/28
(a)The commercial paper program is supported by a revolving credit agreement with various banks (provisions allow for increased borrowings, at the option of Montana-Dakota on stated conditions, up to a maximum of $250.0 million). At December 31, 2024 and 2023, there were no amounts outstanding under the revolving credit agreement.
(b)Certain provisions allow for increased borrowings, up to a maximum of $225.0 million.
(c)Outstanding letter(s) of credit reduce the amount available under the credit agreement.
(d)Certain provisions allow for increased borrowings, up to a maximum of $250.0 million.
Schedule of Long-Term Debt Long-term debt outstanding was as follows:
 
Weighted Average Interest Rate at December 31, 2024
20242023
 (In thousands)
Senior notes due on dates ranging from August 23, 2025 to June 15, 2062
4.57 %$1,947,000 $1,882,000 
Credit agreements due on June 20, 2029
5.79 %169,700 46,100 
Commercial paper supported by revolving credit agreement
4.76 %81,400 144,200 
Term loan agreements due on dates ranging from September 3, 2032 to April 1, 2039
4.44 %65,600 64,300 
Medium-term notes due on dates ranging from September 15, 2027 to March 16, 2029
7.32 %35,000 35,000 
Other notes due on dates ranging from May 31, 2028 to November 30, 2038
6.00 %346 980 
Less unamortized debt issuance costs6,436 6,357 
Total long-term debt2,292,610 2,166,223 
Less current maturities161,700 61,319 
Net long-term debt$2,130,910 $2,104,904 
Schedule of Maturities of Long-Term Debt Long-term debt maturities, which excludes unamortized debt issuance costs and discount, for the five years and thereafter following December 31, 2024, were as follows:
20252026202720282029Thereafter
(In thousands)
Long-term debt maturities$161,700 $144,700 $24,700 $161,100 $244,400 $1,562,446 
v3.25.0.1
Asset Retirement Obligations (Tables)
 12 Months Ended
Dec. 31, 2024
Asset Retirement Obligation [Abstract]  
Schedule of Change in Asset Retirement Obligation
A reconciliation of the Company's liability, which the current portion is included in other accrued liabilities on the Consolidated Balance Sheets, for the years ended December 31 was as follows:
2024 2023 
(In thousands)
Balance at beginning of year$385,154 $373,147 
Liabilities incurred2,721 533 
Liabilities settled(5,271)(6,633)
Accretion expense*19,655 18,894 
Revisions in estimates4,388 (787)
Balance at end of year$406,647 $385,154 
*Includes $19.6 million and $18.9 million in 2024 and 2023, respectively, recorded to regulatory assets.
v3.25.0.1
Stock-Based Compensation (Tables)
 12 Months Ended
Dec. 31, 2024
Share-Based Payment Arrangement [Abstract]  
Schedule of Target Grants of Restricted Stock Units
Target grants of RSUs outstanding at December 31, 2024, were as follows:
Grant DatePerformance PeriodTarget Grant of Shares
February 2023/ July 20232023-2025542,233 
February 2024/ June 20242024-2026698,284 
A summary of the status of the RSUs for the year ended December 31, 2024, was as follows:
RSUs
 
Number of Shares
Weighted
Average
Grant-Date
Fair Value
**
Nonvested at beginning of period873,300 $21.16 
Granted pre-separation of Everus
478,938 20.89 
Forfeited
(112,826)21.35 
Non-vested pre-separation of Everus
1,239,412 
Adjustments related to the Everus separation*
663,661 
Vested shares
(662,556)12.04 
Nonvested at end of period1,240,517 $12.56 
*Includes the conversion adjustments to preserve the intrinsic value of the awards and the cancellation of outstanding awards held by employees that transferred to Everus, which were replaced with awards issued by Everus as part of the separation.
** Weighted average grant-date fair values post-separation of Everus reflects incremental fair value related to modifying the awards and the Company's adjusted stock price due to the separation.
Schedule of Share-Based Payment Award, Performance Shares, Valuation Assumptions Assumptions used for initial grants applicable to the market condition for certain PSAs issued in 2022 were:
2022 
Weighted average grant-date fair value$36.25 
Blended volatility range
24.07% - 31.41%
Risk-free interest rate range
.71% - 1.68%
Weighted average discounted dividends per share$2.93 
v3.25.0.1
Accumulated Other Comprehensive Loss (Tables)
 12 Months Ended
Dec. 31, 2024
Equity [Abstract]  
Schedule of Accumulated Other Comprehensive Income (Loss)
The after-tax changes in the components of accumulated other comprehensive loss were as follows:
 Net
Unrealized
Loss on
Derivative
 Instruments
 Qualifying
as Hedges		Post-
retirement
 Liability
Adjustment		Net
Unrealized
Gain (Loss) on
Available-
for-sale
Investments		Total
Accumulated
 Other
Comprehensive
 Loss
 (In thousands)
At December 31, 2022$(125)$(29,900)$(558)$(30,583)
Other comprehensive income (loss) before reclassifications— (646)173 (473)
Amounts reclassified from accumulated other comprehensive loss81 242 43 366 
Net current-period other comprehensive income (loss)81 (404)216 (107)
Amounts reclassified related to the separation of Knife River44 12,262 — 12,306 
At December 31, 2023— (18,042)(342)(18,384)
Other comprehensive income before reclassifications
— 1,049 85 1,134 
Amounts reclassified from accumulated other comprehensive loss— 432 20 452 
Net current-period other comprehensive income
— 1,481 105 1,586 
At December 31, 2024$— $(16,561)$(237)$(16,798)
Schedule of Reclassification Out of AOCI
The following amounts were reclassified out of accumulated other comprehensive loss into net income. The amounts presented in parentheses indicate a decrease to net income on the Consolidated Statements of Income. The reclassifications for the years ended December 31 were as follows:
 20242023Location on Consolidated
Statements of Income
(In thousands)
Reclassification adjustment for loss on derivative instruments included in net income$— $(96)Interest expense
— 15 Income taxes
— (81)
Amortization of postretirement liability losses included in net periodic benefit credit(577)(320)Other income
145 78 Income taxes
(432)(242)
Reclassification adjustment on available-for-sale investments included in net income(25)(54)Other income
5 11 Income taxes
(20)(43)
Total reclassifications$(452)$(366)
v3.25.0.1
Income Taxes (Tables)
 12 Months Ended
Dec. 31, 2024
Income Tax Disclosure [Abstract]  
Schedule of Income before Income Tax, Domestic and Foreign
The components of income before income taxes from continuing operations for each of the years ended December 31 were as follows:
202420232022
(In thousands)
United States$198,662 $340,330 $123,447 
Income before income taxes from continuing operations$198,662 $340,330 $123,447 
Schedule of Components of Income Tax Expense (Benefit)
Income tax expense (benefit) from continuing operations for the years ended December 31 was as follows:
 2024 2023 2022 
 (In thousands)
Current:   
Federal$30,412 $8,271 $(15,849)
State3,255 3,251 1,857 
 33,667 11,522 (13,992)
Deferred:
Income taxes:
Federal(17,321)(3,331)15,038 
State(1,805)(125)4,251 
Investment tax credit - net3,048 2,147 898 
 (16,078)(1,309)20,187 
Total income tax expense$17,589 $10,213 $6,195 
Schedule of Deferred Tax Assets and Liabilities
Components of deferred tax assets and deferred tax liabilities at December 31 were as follows:
 20242023
 (In thousands)
Deferred tax assets:  
Environmental compliance$33,730 $28,873 
Pension and postretirement25,508 27,584 
Compensation-related15,651 17,106 
Customer advances9,719 8,312 
Cost recovery mechanisms7,402 5,314 
Legal and environmental contingencies5,317 4,881 
Other20,386 13,045 
Total deferred tax assets117,713 105,115 
Deferred tax liabilities:  
Basis differences on property, plant and equipment426,493 404,039 
Pension and postretirement48,355 39,110 
Purchased gas adjustment20,441 34,618 
Environmental compliance17,260 16,221 
Cost recovery mechanisms19,245 22,604 
Legal and environmental contingencies6,300 5,902 
Other19,931 33,947 
Total deferred tax liabilities558,025 556,441 
Valuation allowance1,008 1,010 
Net deferred income tax liability$441,320 $452,336 
Schedule of Change in Net Deferred Income Tax Liability Reconciliation
The following table reconciles the change in the net deferred income tax liability from December 31, 2023, to December 31, 2024, to deferred income tax expense:
 2024
(In thousands)
Change in net deferred income tax liability from the preceding table$(11,016)
Excess deferred income tax amortization(8,121)
Deferred taxes associated with other comprehensive income
(532)
Other3,591 
Deferred income tax expense for the period$(16,078)
Schedule of Effective Income Tax Rate Reconciliation
Total income tax expense differs from the amount computed by applying the statutory federal income tax rate to income before taxes. The reasons for this difference were as follows:
Years ended December 31,202420232022
 Amount%Amount%Amount%
 (Dollars in thousands)
Computed tax at federal statutory rate$41,719 21.0 $71,469 21.0 $25,924 21.0 
Increases (reductions) resulting from:  
State income taxes, net of federal income tax
4,047 2.0 3,605 1.1 2,484 2.0 
State investment tax credit, net of federal income tax2,400 1.2 1,545 .5 1,624 1.3 
Executive compensation2,111 1.1 564 .2 683 .6 
Federal renewable energy credit
(16,871)(8.5)(15,175)(4.5)(15,343)(12.4)
Excess deferred income tax amortization(8,121)(4.1)(8,383)(2.5)(9,008)(7.3)
State tax rate change(2,317)(1.2)(9)— (3)— 
Research and development tax credit(1,465)(.7)(1,985)(.6)(1,692)(1.4)
Nonqualified benefit plans(1,142)(.6)(1,313)(.4)1,516 1.2 
Tax-free debt for equity exchange — — (38,967)(11.4)— — 
Other(2,772)(1.4)(1,138)(.3)10 — 
Total income tax expense$17,589 8.8 $10,213 3.1 $6,195 5.0 
v3.25.0.1
Cash Flow Information (Tables)
 12 Months Ended
Dec. 31, 2024
Supplemental Cash Flow Information [Abstract]  
Schedule of Cash Flow, Supplemental Disclosures
Cash expenditures for interest and income taxes for the years ended December 31 were as follows:
202420232022
 (In thousands)
Interest, net*
$108,242 $112,839 $49,036 
Income taxes paid (refunded), net**
$43,572 $12,162 $(27,884)
*    AFUDC - borrowed was $11.0 million, $10.0 million and $2.2 million for the years ended December 31, 2024, 2023 and 2022, respectively.
**Income taxes paid, including discontinued operations, were $80.9 million, $62.5 million and $26.4 million for the years ended December 31, 2024, 2023 and 2022, respectively.
Noncash investing and financing transactions at December 31 were as follows:
202420232022
 (In thousands)
Property, plant and equipment additions in accounts payable$36,820 $46,364 $34,886 
Right-of-use assets obtained in exchange for new operating lease liabilities$1,787 $2,265 $1,324 
Debt for equity exchange of retained shares in Knife River
$— $293,239 $— 
v3.25.0.1
Business Segment Data (Tables)
 12 Months Ended
Dec. 31, 2024
Segment Reporting [Abstract]  
Schedule of Segment Reporting Information, by Segment Information on the Company's segments as of December 31 and for the years then ended was as follows:
Year ended December 31, 2024ElectricNatural gas distributionPipelineOtherConsolidated
(In thousands)
Operating revenues:
External operating revenues$414,406 $1,200,975 $142,597 $— $1,757,978 
Intersegment operating revenues72 130 69,222 195 69,619 
Operation and maintenance:
External operation and maintenance94,897 231,087 75,456 13,051 414,491 
Intersegment operation and maintenance72 130 324 195 721 
Purchased natural gas sold:
External purchased natural gas sold— 630,403 — — 630,403 
Intersegment purchased natural gas sold— 68,898 — — 68,898 
Electric fuel and purchased power
141,148 — — — 141,148 
Depreciation and amortization66,524 101,958 29,362 2,234 200,078 
Taxes, other than income17,605 76,042 12,175 394 106,216 
Other income:
External other income
8,205 25,509 5,850 1,803 41,367 
Intersegment other income
— — 655 14,798 15,453 
Interest expense:
External interest expense30,058 63,185 10,862 4,242 108,347 
Intersegment interest expense— — 4,633 10,820 15,453 
Income tax expense (benefit)
(2,414)7,974 17,470 (5,441)17,589 
Income (loss) from continuing operations
74,793 46,937 68,042 (8,699)181,073 
Discontinued operations, net of tax— — — 100,035 100,035 
Net income$74,793 $46,937 $68,042 $91,336 $281,108 
Capital expenditures (a)
$110,812 $286,152 $126,806 $1,728 $525,498 
Assets$1,976,912 
(b)
$3,730,532 (b)$1,151,317 $180,057 
(c)
$7,038,818 
Property, plant and equipment$2,480,816 (b)$3,731,093 (b)$1,338,006 $4,148 $7,554,063 
Accumulated depreciation and amortization
$716,736 
(b)
$1,139,223 
(b)
$351,045 $2,767 $2,209,771 
(a)Capital expenditures include noncash transactions such as capital expenditure-related accounts payable and AFUDC totaling $7.1 million.
(b)Includes allocations of common utility property for the Electric and Natural gas distribution segments.
(c)Other includes assets not directly assignable to a business (i.e. cash, cash equivalents and restricted cash, certain accounts receivable, certain investments and other miscellaneous current and deferred assets).
Year ended December 31, 2023ElectricNatural gas distributionPipelineOtherConsolidated
(In thousands)
Operating revenues:
External operating revenues$401,037 $1,287,236 $115,079 $— $1,803,352 
Intersegment operating revenues138 301 62,533 119 63,091 
Operation and maintenance:
External operation and maintenance92,521 219,481 70,386 24,693 407,081 
Intersegment operation and maintenance138 301 431 119 989 
Purchased natural gas sold:
External purchased natural gas sold— 742,965 — — 742,965 
Intersegment purchased natural gas sold— 62,102 — — 62,102 
Electric fuel and purchased power
134,779 — — — 134,779 
Depreciation and amortization64,253 95,300 26,811 4,086 190,450 
Taxes, other than income16,695 75,207 10,822 409 103,133 
Realized gain on tax-free exchange of the retained shares in Knife River— — — 186,556 186,556 
Other income:
External other income5,815 20,867 3,675 3,097 33,454 
Intersegment other income— — 217 13,431 13,648 
Interest expense:
External interest expense28,064 57,601 9,428 9,531 104,624 
Intersegment interest expense— — 3,842 9,806 13,648 
Income tax expense (benefit)
(1,019)6,927 12,409 (8,104)10,213 
Income from continuing operations
71,559 48,520 47,375 162,663 330,117 
Discontinued operations, net of tax— — (457)85,047 84,590 
Net income$71,559 $48,520 $46,918 $247,710 $414,707 
Capital expenditures (a)
$109,805 $274,836 $115,903 $(2,825)$497,719 
Assets$1,955,644 
(b)
$3,532,142 
(b)
$1,045,704 $1,299,669 
(c)
$7,833,159 
Property, plant and equipment
$2,369,039 
(b)
$3,462,187 
(b)
$1,218,387 $31,654 $7,081,267 
Accumulated depreciation and amortization
$660,438 
(b)
$1,068,037 
(b)
$328,010 $19,890 $2,076,375 
(a)Capital expenditures include noncash transactions such as capital expenditure-related accounts payable and AFUDC totaling $(13.6) million.
(b)Includes allocations of common utility property for the Electric and Natural gas distribution segments.
(c)Other includes assets of discontinued operations and assets not directly assignable to a business (i.e. cash, cash equivalents and restricted cash, certain accounts receivable, certain investments and other miscellaneous current and deferred assets).
Year ended December 31, 2022ElectricNatural gas distributionPipelineOtherConsolidated
(In thousands)
Operating revenues:
External operating revenues$377,015 $1,273,588 $96,695 $— $1,747,298 
Intersegment operating revenues58 216 58,884 86 59,244 
Operation and maintenance:
External operation and maintenance93,236 205,009 60,300 21,406 379,951 
Intersegment operation and maintenance58 216 638 86 998 
Purchased natural gas sold:
External purchased natural gas sold— 757,883 — — 757,883 
Intersegment purchased natural gas sold— 58,246 — — 58,246 
Electric fuel and purchased power
119,405 — — — 119,405 
Depreciation and amortization67,802 89,466 26,857 4,435 188,560 
Taxes, other than income16,917 71,095 12,318 299 100,629 
Other income:
External other income528 3,213 1,272 (1,753)3,260 
Intersegment other income— — 80 556 636 
Interest expense:
External interest expense28,526 42,126 9,966 65 80,683 
Intersegment interest expense— — 136 500 636 
Income tax expense (benefit)
(5,420)7,805 10,522 (6,712)6,195 
Income (loss) from continuing operations
57,077 45,171 36,194 (21,190)117,252 
Discontinued operations, net of tax— — (906)251,143 250,237 
Net income$57,077 $45,171 $35,288 $229,953 $367,489 
Capital expenditures (a)
$133,970 $240,064 $61,923 $2,272 $438,229 
Assets$1,856,258 
(b)
$3,214,452 
(b)
$961,893 $3,628,178 
(c)
$9,660,781 
Property, plant and equipment
$2,276,613 
(b)
$3,208,059 
(b)
$1,108,141 $36,705 $6,629,518 
Accumulated depreciation and amortization
$625,813 
(b)
$1,009,788 
(b)
$308,516 $19,143 $1,963,260 
(a)Capital expenditures include noncash transactions such as capital expenditure-related accounts payable and AFUDC totaling $4.4 million.
(b)Includes allocations of common utility property for the Electric and Natural gas distribution segments.
(c)Other includes assets of discontinued operations and assets not directly assignable to a business (i.e. cash, cash equivalents and restricted cash, certain accounts receivable, certain investments and other miscellaneous current and deferred assets).
Schedule of Reconciliation of Revenue from Segments to Consolidated
A reconciliation of reportable segment operating revenues and assets to consolidated operating revenues and assets is as follows:
20242023 2022 
(In thousands)
Operating revenues reconciliation:
Total reportable segment operating revenues$1,827,402 $1,866,324 $1,806,456 
Other revenue195 119 86 
Elimination of intersegment operating revenues(69,619)(63,091)(59,244)
Total consolidated operating revenues$1,757,978 $1,803,352 $1,747,298 
Asset reconciliation:
Total reportable segment assets$6,892,959 $6,564,962 $6,061,151 
Other assets525,258 1,847,432 4,784,142 
Elimination of intersegment receivables(379,399)(579,235)(1,184,512)
Total consolidated assets$7,038,818 $7,833,159 $9,660,781 
Schedule of Reconciliation of Assets from Segment to Consolidated
A reconciliation of reportable segment operating revenues and assets to consolidated operating revenues and assets is as follows:
20242023 2022 
(In thousands)
Operating revenues reconciliation:
Total reportable segment operating revenues$1,827,402 $1,866,324 $1,806,456 
Other revenue195 119 86 
Elimination of intersegment operating revenues(69,619)(63,091)(59,244)
Total consolidated operating revenues$1,757,978 $1,803,352 $1,747,298 
Asset reconciliation:
Total reportable segment assets$6,892,959 $6,564,962 $6,061,151 
Other assets525,258 1,847,432 4,784,142 
Elimination of intersegment receivables(379,399)(579,235)(1,184,512)
Total consolidated assets$7,038,818 $7,833,159 $9,660,781 
v3.25.0.1
Employee Benefit Plans (Tables)
 12 Months Ended
Dec. 31, 2024
Retirement Benefits [Abstract]  
Schedule of Amounts Recognized in Balance Sheet
Changes in benefit obligation and plan assets and amounts recognized in the Consolidated Balance Sheets at December 31 were as follows:
 Pension BenefitsOther
Postretirement Benefits
 2024202320242023
Change in benefit obligation:(In thousands)
Benefit obligation at beginning of year$275,586 $278,286 $39,590 $40,315 
Service cost— — 505 534 
Interest cost12,799 13,521 1,837 1,956 
Plan participants' contributions— — 412 479 
Actuarial (gain) loss
(11,040)5,395 (3,420)(215)
Benefits paid(21,995)(21,616)(3,249)(3,479)
Benefit obligation at end of year255,350 275,586 35,675 39,590 
Change in net plan assets:    
Fair value of plan assets at beginning of year248,558 242,031 79,234 76,640 
Actual return on plan assets1,152 20,576 2,297 5,518 
Employer contribution2,911 7,567 71 76 
Plan participants' contributions— — 412 479 
Benefits paid(21,995)(21,616)(3,249)(3,479)
Fair value of net plan assets at end of year230,626 248,558 78,765 79,234 
Funded status - (under) over$(24,724)$(27,028)$43,090 $39,644 
Amounts recognized in the Consolidated Balance Sheets at December 31:    
Noncurrent assets - other$— $— $43,090 $39,644 
Noncurrent liabilities - other24,724 27,028 — — 
Benefit obligation (liabilities) assets - net amount recognized$(24,724)$(27,028)$43,090 $39,644 
Amounts recognized in accumulated other comprehensive loss:    
Actuarial loss (gain)$13,228 $32,273 $(809)$(3,515)
Prior service credit— — (37)(115)
Total$13,228 $32,273 $(846)$(3,630)
Amounts recognized in regulatory assets or liabilities:    
Actuarial loss (gain)$139,962 $140,232 $(1,478)$(1,146)
Prior service credit— — (1,303)(2,619)
Total$139,962 $140,232 $(2,781)$(3,765)
Schedule of Accumulated and Projected Benefit Obligations
The pension plans all have accumulated benefit obligations in excess of plan assets. The projected benefit obligation, accumulated benefit obligation and fair value of plan assets for these plans at December 31 were as follows:
 2024 2023 
 (In thousands)
Projected benefit obligation$255,350 $275,586 
Accumulated benefit obligation$255,350 $275,586 
Fair value of plan assets$230,626 $248,558 
The projected benefit obligation and accumulated benefit obligation for these plans at December 31 were as follows:
 2024 2023 
 (In thousands)
Projected benefit obligation$52,007 $57,033 
Accumulated benefit obligation$52,007 $57,033 
Schedule of Net Benefit Costs
The components of net periodic benefit cost (credit), other than the service cost component, are included in other income on the Consolidated Statements of Income. Prior service credit is amortized on a straight-line basis over the average remaining service period of active participants. These components related to the Company's pension and other postretirement benefit plans for the years ended December 31 were as follows:
 Pension BenefitsOther
Postretirement Benefits
 202420232022202420232022
Components of net periodic benefit cost (credit):
(In thousands)
Service cost$— $— $— $505 $534 $894 
Interest cost12,799 13,521 9,396 1,837 1,956 1,383 
Expected return on assets(16,113)(17,194)(17,482)(5,315)(5,361)(5,277)
Amortization of prior service credit— — — (1,318)(1,318)(1,318)
Recognized net actuarial loss (gain)4,149 3,093 5,826 (288)(504)(570)
Net periodic benefit cost (credit), including amount capitalized
835 (580)(2,260)(4,579)(4,693)(4,888)
Less amount capitalized— — — — 107 175 
Net periodic benefit cost (credit)
835 (580)(2,260)(4,579)(4,800)(5,063)
Other changes in plan assets and benefit obligations recognized in accumulated comprehensive loss:    
Net loss (gain)
401 187 2,369 71 (604)(4,141)
Amortization of actuarial (loss) gain(359)(292)(1,310)130 108 (281)
Amortization of prior service credit— — — 45 78 125 
Reclassification of postretirement liability adjustment from regulatory asset— — 5,343 — — (992)
Total recognized in accumulated other comprehensive loss42 (105)6,402 246 (418)(5,289)
Other changes in plan assets and benefit obligations recognized in regulatory assets or liabilities:    
Net loss (gain)
3,520 1,826 9,757 (472)(107)11,920 
Amortization of actuarial (loss) gain(3,790)(2,801)(5,373)158 304 500 
Amortization of prior service credit— — — 1,273 1,273 1,273 
Reclassification of postretirement liability adjustment from regulatory asset— — (5,343)— — 992 
Total recognized in regulatory assets or liabilities(270)(975)(959)959 1,470 14,685 
Total recognized in net periodic benefit credit, accumulated other comprehensive loss and regulatory assets or liabilities$607 $(1,660)$3,183 $(3,374)$(3,748)$4,333 
The components of net periodic benefit cost are included in other income on the Consolidated Statements of Income. These components related to the Company's nonqualified defined benefit plans for the years ended December 31 were as follows:
 2024 2023 2022 
 (In thousands)
Components of net periodic benefit cost:   
Interest cost$2,568 $2,740 $1,681 
Recognized net actuarial loss365 273 911 
Net periodic benefit cost$2,933 $3,013 $2,592 
Defined Benefit Plan, Assumptions
Weighted average assumptions used to determine benefit obligations at December 31 were as follows:
 Pension BenefitsOther
Postretirement Benefits
 2024 2023 2024 2023 
Discount rate5.41 %4.84 %5.43 %4.85 %
Expected return on plan assets6.50 %6.50 %6.00 %6.00 %
Weighted average assumptions used to determine net periodic benefit cost (credit) for the years ended December 31 were as follows:
 Pension BenefitsOther
Postretirement Benefits
 2024202320242023
Discount rate4.84 %5.06 %4.85 %5.07 %
Expected return on plan assets6.50 %6.50 %6.00 %6.00 %
Weighted average assumptions used at December 31 were as follows:
 2024 2023 
Benefit obligation discount rate5.26 %4.73 %
Benefit obligation rate of compensation increaseN/AN/A
Net periodic benefit cost discount rate4.73 %4.97 %
Net periodic benefit cost rate of compensation increaseN/AN/A
Schedule of Health Care Cost Trend Rates
Health care rate assumptions for the Company's other postretirement benefit plans as of December 31 were as follows:
 2024 2023 
Health care trend rate assumed for next year (pre-65/post-65)
8.5%/6.25%
7.5%/6.5%
Health care cost trend rate - ultimate4.5 %4.5 %
Year in which ultimate trend rate achieved (pre-65/post-65)
2035/20342034/2033
Schedule of Expected Benefit Payments
The following benefit payments, which reflect future service, as appropriate, and expected Medicare Part D subsidies at December 31, 2024, are as follows:
YearsPension
Benefits		Other
Postretirement Benefits		Expected
Medicare
Part D Subsidy
 (In thousands)
2025$22,280 $3,333 $48 
2026$22,070 $3,235 $43 
2027$21,870 $3,153 $37 
2028$21,500 $3,064 $32 
2029$21,170 $2,941 $27 
2030-2034$98,020 $13,659 $85 
The amount of future benefit payments for the unfunded, nonqualified defined benefit plans at December 31, 2024, are expected to aggregate as follows:
202520262027202820292030-2034
(In thousands)
Nonqualified benefits$5,700 $5,610 $5,830 $5,560 $5,190 $20,920 
Schedule of Allocation of Plan Assets
The fair value of the Company's pension plans' assets (excluding cash) by class were as follows:
 
Fair Value Measurements
 at December 31, 2024, Using
 
 Quoted Prices
in Active
Markets for
Identical
Assets
 (Level 1)		Significant
Other
Observable
Inputs
 (Level 2)		Significant
Unobservable
 Inputs
 (Level 3)		Balance at December 31, 2024
 (In thousands)
Assets:    
Cash equivalents$— $4,512 $— $4,512 
Equity securities: 
U.S. companies(2)— — (2)
Collective and mutual funds (a)72,777 93,606 — 166,383 
U.S. Government securities33,616 25,857 — 59,473 
Investments measured at net asset value (b)— — — 260 
Total assets measured at fair value$106,391 $123,975 $— $230,626 
(a)Collective and mutual funds invest approximately 39 percent in corporate bonds, 19 percent in U.S. Government securities, 17 percent in other investments, 15 percent in common stock of international companies, 9 percent in common stock of large-cap and mid-cap U.S. companies, and 1 percent cash and cash equivalents.
(b)In accordance with ASC 820 - Fair Value Measurements, certain investments that were measured at net asset value per share (or its equivalent) have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the line items presented in the Consolidated Balance Sheets.
 
Fair Value Measurements
 at December 31, 2023, Using
 
 Quoted Prices
in Active
Markets for
Identical
Assets
 (Level 1)		Significant
Other
Observable
Inputs
 (Level 2)		Significant
Unobservable
 Inputs
 (Level 3)		Balance at December 31, 2023
 (In thousands)
Assets:    
Cash equivalents$— $7,197 $— $7,197 
Equity securities: 
U.S. companies(2)— — (2)
Collective and mutual funds (a)84,761 88,219 — 172,980 
U.S. Government securities30,162 33,141 — 63,303 
Investments measured at net asset value (b)
— — — 5,080 
Total assets measured at fair value$114,921 $128,557 $— $248,558 
(a)Collective and mutual funds invest approximately 51 percent in corporate bonds, 15 percent in common stock of international companies, 11 percent in common stock of large-cap and mid-cap U.S. companies, 7 percent cash and cash equivalents, 7 percent in U.S. Government securities and 9 percent in other investments.
(b)In accordance with ASC 820 - Fair Value Measurements, certain investments that were measured at net asset value per share (or its equivalent) have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the line items presented in the Consolidated Balance Sheets.
The fair value of the Company's other postretirement benefit plans' assets (excluding cash) by asset class were as follows:
 Fair Value Measurements
 at December 31, 2024, Using		 
 Quoted Prices
in Active
Markets for
Identical
Assets
 (Level 1)		Significant
Other
Observable
Inputs
 (Level 2)		Significant
Unobservable
 Inputs
 (Level 3)		Balance at December 31, 2024
 (In thousands)
Assets:    
Cash equivalents$— $4,373 $— $4,373 
Equity securities: 
U.S. companies2,880 — — 2,880 
Insurance contract (a)— 71,512 — 71,512 
Total assets measured at fair value$2,880 $75,885 $— $78,765 
(a)The insurance contract invests approximately 41 percent in corporate bonds, 28 percent in U.S. Government securities, 19 percent in common stock of large-cap U.S. companies, 6 percent in common stock of small-cap U.S. companies and 6 percent in other investments.
 Fair Value Measurements
 at December 31, 2023, Using		 
 Quoted Prices
in Active
Markets for
Identical
Assets
 (Level 1)		Significant
Other
Observable
Inputs
 (Level 2)		Significant
Unobservable
 Inputs
 (Level 3)		Balance at December 31, 2023
 (In thousands)
Assets:    
Cash equivalents$— $4,562 $— $4,562 
Equity securities: 
U.S. companies2,369 — — 2,369 
Insurance contract (a)— 72,303 — 72,303 
Total assets measured at fair value$2,369 $76,865 $— $79,234 
(a)The insurance contract invests approximately 60 percent in corporate bonds, 16 percent in common stock of large-cap U.S. companies, 15 percent in U.S. Government securities, 5 percent in common stock of small-cap U.S. companies and 4 percent in other investments.
The amount of investments that the Company anticipates using to satisfy obligations under these plans at December 31 was as follows:
2024 2023 
(In thousands)
Investments
Insurance contracts*$59,282 $62,936 
Life insurance**30,834 31,303 
Other12,879 6,409 
Total investments$102,995 $100,648 
*For more information on the insurance contracts, see Note 9.
**Investments of life insurance are carried on plan participants (payable upon the employee's death).
Schedule of Multiemployer Plans
EIN/Pension Plan NumberPension Protection Act Zone StatusFIP/RP Status Pending/ImplementedContributionsSurcharge ImposedExpiration Date
of Collective
Bargaining
Agreement
Pension Fund202420232024 2023 2022 
(In thousands)
Idaho Plumbers and Pipefitters Pension Plan
826010346-001
Green as of 5/31/2024
Green as of 5/31/2023
No$1,434 $1,690 $1,613 No3/31/2027
Total contributions$1,434 $1,690 $1,613 
The Company was listed in the plans' Forms 5500 as providing more than 5 percent of the total contributions for the following plans and plan years:
Pension FundYear Contributions to Plan Exceeded More Than 5 Percent
of Total Contributions (as of December 31 of the Plan's Year-End)
Idaho Plumbers and Pipefitters Pension Plan2023 and 2022
v3.25.0.1
Commitments and Contingencies (Tables)
 12 Months Ended
Dec. 31, 2024
Commitments and Contingencies Disclosure [Abstract]  
Schedule of Long-Term Purchase Commitment The commitment terms vary in length, up to 35 years. The commitments under these contracts as of December 31, 2024, were:
20252026202720282029Thereafter
(In thousands)
Purchase commitments$658,012 $310,894 $210,152 $177,613 $147,081 $1,221,125 
Schedule of Lease Costs
The following tables provide information on the Company's operating leases at and for the years ended December 31:
202420232022
(In thousands)
Lease costs:
Short-term lease cost$1,549 $1,646 $1,373 
Operating lease cost3,069 2,871 2,497 
Variable lease cost819 676 413 
$5,437 $5,193 $4,283 
202420232022
(Dollars in thousands)
Weighted average remaining lease term12.65 years15.35 years15.15 years
Weighted average discount rate6.08 %4.88 %4.65 %
Cash paid for amounts included in the measurement of lease liabilities
$3,063$2,868 $2,500 
Schedule of Operating Lease Liabilities Undiscounted Cash Flows Maturity
The reconciliation of future undiscounted cash flows to operating lease liabilities presented on the Consolidated Balance Sheet at December 31, 2024, was as follows:
(In thousands)
2025$3,034 
20262,648 
20272,011 
20281,570 
20291,492 
Thereafter20,808 
Total31,563 
Less discount10,654 
Total operating lease liabilities$20,909 
v3.25.0.1
Jointly Owned Facilities (Tables)
 12 Months Ended
Dec. 31, 2024
Regulated Operations [Abstract]  
Schedule of Jointly Owned Utility Plants
At December 31, the Company's share of the cost of utility plant in service, construction work in progress and related accumulated depreciation for the jointly owned facilities was as follows:
Ownership Percentage20242023
 (In thousands)
Big Stone Station:22.7 %
Utility plant in service$155,302 $159,437 
CWIP
318 197 
Less accumulated depreciation55,327 52,264 
$100,293 $107,370 
BSSE:50.0 %
Utility plant in service$111,043 $107,260 
CWIP
— — 
Less accumulated depreciation10,359 8,111 
$100,684 $99,149 
Coyote Station:25.0 %
Utility plant in service$160,343 $160,208 
CWIP
755 159 
Less accumulated depreciation115,133 113,187 
$45,965 $47,180 
JETx:
50.0 %
Utility plant in service$— $— 
CWIP
6,112 1,372 
Less accumulated depreciation— — 
$6,112 $1,372 
Wygen III:25.0 %
Utility plant in service$67,851 $66,852 
CWIP
97 127 
Less accumulated depreciation15,340 13,728 
$52,608 $53,251 
v3.25.0.1
Basis of Presentation (Details)
$ in Thousands, shares in Millions
 12 Months Ended
Oct. 31, 2024
May 31, 2023
shares
Dec. 31, 2024
USD ($)
Dec. 31, 2023
USD ($)
Dec. 31, 2022
USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]          
Electric fuel and purchased power     $ 141,148 $ 134,779 $ 119,405
Operation and maintenance     $ (414,491) (407,081) (379,951)
Revision of Prior Period, Error Correction, Adjustment          
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]          
Electric fuel and purchased power       26,900 27,400
Operation and maintenance       $ 26,900 $ 27,400
Discontinued Operations, Disposed of by Means Other than Sale, Spinoff | Knife River Corporation          
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]          
Pro rata distribution of shares, percentage   0.90      
Stock split, conversion ratio   0.25      
Retained ownership percentage   0.10      
Number of retained shares (in shares) | shares   5.7      
Discontinued Operations, Disposed of by Means Other than Sale, Spinoff | Everus          
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]          
Stock split, conversion ratio 0.25        
v3.25.0.1
Significant Accounting Policies - Cash, Cash Equivalents And Restricted Cash (Details) - USD ($)
$ in Millions
Dec. 31, 2024
Dec. 31, 2023
Accounting Policies [Abstract]    
Restricted cash $ 16.7 $ 13.2
v3.25.0.1
Significant Accounting Policies - Receivables And Allowance For Expected Credit Losses (Details) - USD ($)
$ in Millions
Dec. 31, 2024
Dec. 31, 2023
Accounting Policies [Abstract]    
Accounts receivable, 90 days or more past due $ 3.6 $ 3.7
Accrued unbilled revenue $ 143.2 $ 132.0
v3.25.0.1
Significant Accounting Policies - Schedule of Expected Credit Loss (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Accounts Receivable, Allowance for Credit Loss [Roll Forward]      
Current expected credit loss provision $ 6,558 $ 7,422 $ 5,409
Trade Accounts Receivable      
Accounts Receivable, Allowance for Credit Loss [Roll Forward]      
Accounts receivable, allowance for credit loss, beginning balance 1,603 1,992  
Current expected credit loss provision 6,558 7,422  
Less write-offs charged against the allowance 7,927 9,351  
Credit loss recoveries collected 1,605 1,540  
Accounts receivable, allowance for credit loss, ending balance 1,839 1,603 1,992
Trade Accounts Receivable | Electric      
Accounts Receivable, Allowance for Credit Loss [Roll Forward]      
Accounts receivable, allowance for credit loss, beginning balance 414 375  
Current expected credit loss provision 1,891 1,645  
Less write-offs charged against the allowance 2,218 1,994  
Credit loss recoveries collected 386 388  
Accounts receivable, allowance for credit loss, ending balance 473 414 375
Trade Accounts Receivable | Natural gas distribution      
Accounts Receivable, Allowance for Credit Loss [Roll Forward]      
Accounts receivable, allowance for credit loss, beginning balance 1,189 1,615  
Current expected credit loss provision 4,667 5,777  
Less write-offs charged against the allowance 5,709 7,355  
Credit loss recoveries collected 1,219 1,152  
Accounts receivable, allowance for credit loss, ending balance 1,366 1,189 1,615
Trade Accounts Receivable | Pipeline      
Accounts Receivable, Allowance for Credit Loss [Roll Forward]      
Accounts receivable, allowance for credit loss, beginning balance 0 2  
Current expected credit loss provision 0 0  
Less write-offs charged against the allowance 0 2  
Credit loss recoveries collected 0 0  
Accounts receivable, allowance for credit loss, ending balance $ 0 $ 0 $ 2
v3.25.0.1
Significant Accounting Policies - Inventories And Natural Gas In Storage (Details) - USD ($)
$ in Thousands
Dec. 31, 2024
Dec. 31, 2023
Accounting Policies [Abstract]    
Natural gas in storage (current) $ 40,073 $ 39,377
Fuel stock 4,867 5,307
Total 44,940 44,684
Natural gas in storage (noncurrent) $ 48,500 $ 48,500
v3.25.0.1
Significant Accounting Policies - Schedule of Property, Plant and Equipment (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Accounting Policies [Abstract]      
AFUDC - borrowed $ 10,964 $ 10,035 $ 2,236
AFUDC - equity $ 2,251 $ 1,894 $ 2,165
v3.25.0.1
Significant Accounting Policies - Impairment of Long-Lived Assets, Excluding Goodwill (Details) - USD ($)
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Accounting Policies [Abstract]      
Impairment losses $ 0 $ 0 $ 0
v3.25.0.1
Significant Accounting Policies - Goodwill (Details) - USD ($)
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Accounting Policies [Abstract]      
Goodwill, impairment loss $ 0 $ 0 $ 0
v3.25.0.1
Significant Accounting Policies - Earnings Per Share (Details) - $ / shares
 12 Months Ended
May 31, 2023
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Weighted average common shares outstanding - basic (in shares)   203,867,000 203,640,000 203,358,000
Effect of dilutive performance share awards (in shares)   786,000 298,000 104,000
Weighted average common shares outstanding - diluted (in shares)   204,653,000 203,938,000 203,462,000
Earnings per share - basic:        
Income from continuing operations (in usd per share)   $ 0.89 $ 1.62 $ 0.58
Discontinued operations, net of tax (in usd per share)   0.49 0.42 1.23
Earnings per share - basic (in usd per share)   1.38 2.04 1.81
Earnings per share - diluted:        
Income from continuing operations (in usd per share)   0.88 1.62 0.58
Discontinued operations, net of tax (in usd per share)   0.49 0.41 1.23
Earnings per share - diluted (in usd per share)   $ 1.37 $ 2.03 $ 1.81
Shares excluded from the calculation of diluted earnings per share (in shares)   0 0 14,000
Dividends declared per common share (in usd per share)   $ 0.5100 $ 0.6950 $ 0.8750
Discontinued Operations, Disposed of by Means Other than Sale, Spinoff | Knife River Corporation        
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Treasury stock, retired (in shares) 538,921      
v3.25.0.1
Significant Accounting Policies - Income Taxes (Details)
 12 Months Ended
Dec. 31, 2024
Accounting Policies [Abstract]  
Threshold of likelihood of tax positions being realized upon ultimate settlement with a taxing authority 0.50
v3.25.0.1
Discontinued Operations - Narrative (Details)
$ in Thousands
 1 Months Ended 12 Months Ended
Oct. 31, 2024
May 31, 2023
shares
Apr. 25, 2023
USD ($)
Nov. 30, 2023
USD ($)
Dec. 31, 2024
USD ($)
Dec. 31, 2023
USD ($)
Dec. 31, 2022
USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]              
Realized gain on tax-free exchange of the retained shares in Knife River         $ 0 $ 186,556 $ 0
Long-term debt         2,292,610 2,166,223  
Repayments of long-term debt         $ 182,135 $ 568,883 $ 38,764
Restructuring Charges, Statement of Income or Comprehensive Income [Extensible Enumeration]         Income from discontinued operations, net of tax Income from discontinued operations, net of tax Income from discontinued operations, net of tax
Knife River Corporation              
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]              
Repayments of long-term debt     $ 825,000        
Knife River Corporation | Revolving Credit Facility              
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]              
Line of credit facility, maximum borrowing capacity     350,000        
Knife River Corporation | Term Loan Agreement              
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]              
Debt instrument, face amount     275,000        
Senior Notes | Knife River Corporation              
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]              
Long-term debt     $ 425,000        
Discontinued Operations, Disposed of by Means Other than Sale, Spinoff | Knife River Corporation              
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]              
Pro rata distribution of shares, percentage   0.90          
Stock split, conversion ratio   0.25          
Retained ownership percentage   0.10          
Number of retained shares (in shares) | shares   5,700,000          
Realized gain on tax-free exchange of the retained shares in Knife River       $ 186,600      
Separation of Knife River (in shares) | shares   538,921          
Separation related costs         $ 41,700 $ 58,600 $ 11,500
Discontinued Operations, Disposed of by Means Other than Sale, Spinoff | Knife River Corporation | Cash Received, TSA              
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]              
Discontinued operation, amount of continuing cash flows after disposal         1,500 2,900  
Discontinued Operations, Disposed of by Means Other than Sale, Spinoff | Knife River Corporation | Cash Paid, TSA              
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]              
Discontinued operation, amount of continuing cash flows after disposal         $ 159 $ 823  
Discontinued Operations, Disposed of by Means Other than Sale, Spinoff | Everus              
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]              
Stock split, conversion ratio 0.25            
Discontinued operation, period of continuing involvement         18 months    
Discontinued Operations, Disposed of by Means Other than Sale, Spinoff | Everus | Maximum              
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]              
Discontinued operation, period of continuing involvement         2 years    
Discontinued Operations, Disposed of by Means Other than Sale, Spinoff | Everus | Cash Received, TSA              
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]              
Discontinued operation, amount of continuing cash flows after disposal         $ 727    
Discontinued Operations, Disposed of by Means Other than Sale, Spinoff | Everus | Cash Paid, TSA              
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]              
Discontinued operation, amount of continuing cash flows after disposal         $ 47    
v3.25.0.1
Discontinued Operations - Schedule of Assets and Liabilities of Discontinued Operations (Details) - USD ($)
$ in Thousands
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Current assets:      
Cash and cash equivalents   $ 16,500 $ 9,700
Noncurrent assets:      
Noncurrent assets of discontinued operations $ 0 347,865  
Current liabilities:      
Total current liabilities of discontinued operations 0 443,280  
Noncurrent liabilities:      
Total noncurrent liabilities of discontinued operations $ 0 179,650  
Everus Corporation | Discontinued Operations, Disposed of by Means Other than Sale, Spinoff      
Current assets:      
Cash and cash equivalents   16,501  
Receivables, net   692,629  
Inventories   42,709  
Prepayments and other current assets   17,651  
Total current assets of discontinued operations   769,490  
Noncurrent assets:      
Net property, plant and equipment   116,018  
Goodwill   143,224  
Other intangible assets, net   2,004  
Investments   11,760  
Operating lease right-of-use assets   53,232  
Other   21,627  
Noncurrent assets of discontinued operations   347,865  
Total assets of discontinued operations   1,117,355  
Current liabilities:      
Accounts payable   315,240  
Taxes payable   8,557  
Accrued compensation   44,721  
Operating lease liabilities due within one year   21,143  
Other accrued liabilities   53,619  
Total current liabilities of discontinued operations   443,280  
Noncurrent liabilities:      
Long-term debt   132,000  
Deferred income taxes   6,212  
Operating lease liabilities   32,504  
Other   8,934  
Total noncurrent liabilities of discontinued operations   179,650  
Total liabilities of discontinued operations   $ 622,930  
v3.25.0.1
Discontinued Operations - Schedule of Income and Expense Constituting Pretax Income From Discontinued Operations (Details) - Knife River Corporation - Discontinued Operations, Disposed of by Means Other than Sale, Spinoff - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]      
Operating revenues $ 2,377,332 $ 3,589,251 $ 5,226,766
Operating expenses 2,241,162 3,422,393 4,853,408
Operating (loss) income 136,170 166,858 373,358
Other income (expense) 12,446 10,599 4,119
Interest expense 7,118 47,229 38,590
Income from discontinued operations before income taxes 141,498 130,228 338,887
Income taxes 41,463 45,638 88,650
Discontinued operations, net of tax $ 100,035 $ 84,590 $ 250,237
v3.25.0.1
Revenue from Contracts with Customers - Schedule of Disaggregation of Revenue (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Disaggregation of Revenue [Line Items]      
Revenues from contracts with customers $ 1,752,995 $ 1,805,807 $ 1,754,158
Other revenues 4,983 (2,455) (6,860)
Total external operating revenues 1,757,978 1,803,352 1,747,298
Operating Segments      
Disaggregation of Revenue [Line Items]      
Total external operating revenues 1,827,402 1,866,324 1,806,456
Intersegment eliminations      
Disaggregation of Revenue [Line Items]      
Revenues from contracts with customers (69,619) (63,091) (59,244)
Total external operating revenues (69,619) (63,091) (59,244)
Natural gas transportation      
Disaggregation of Revenue [Line Items]      
Revenues from contracts with customers 235,268 197,762 178,176
Natural gas storage      
Disaggregation of Revenue [Line Items]      
Revenues from contracts with customers 23,690 18,254 14,583
Other      
Disaggregation of Revenue [Line Items]      
Revenues from contracts with customers 113,325 83,642 70,761
Residential utility sales      
Disaggregation of Revenue [Line Items]      
Revenues from contracts with customers 786,103 860,874 856,825
Commercial utility sales      
Disaggregation of Revenue [Line Items]      
Revenues from contracts with customers 570,847 612,828 599,984
Industrial utility sales      
Disaggregation of Revenue [Line Items]      
Revenues from contracts with customers 85,471 88,268 85,476
Other utility sales      
Disaggregation of Revenue [Line Items]      
Revenues from contracts with customers 7,910 7,270 7,597
Electric | Operating Segments      
Disaggregation of Revenue [Line Items]      
Revenues from contracts with customers 421,823 411,298 381,729
Other revenues (7,417) (10,261) (4,714)
Total external operating revenues 414,406 401,037 377,015
Electric | Intersegment eliminations      
Disaggregation of Revenue [Line Items]      
Revenues from contracts with customers (72) (138) (58)
Total external operating revenues (72) (138) (58)
Electric | Natural gas transportation | Operating Segments      
Disaggregation of Revenue [Line Items]      
Revenues from contracts with customers 0 0 0
Electric | Natural gas storage | Operating Segments      
Disaggregation of Revenue [Line Items]      
Revenues from contracts with customers 0 0 0
Electric | Other | Operating Segments      
Disaggregation of Revenue [Line Items]      
Revenues from contracts with customers 59,288 54,508 45,608
Electric | Residential utility sales | Operating Segments      
Disaggregation of Revenue [Line Items]      
Revenues from contracts with customers 140,054 136,274 138,634
Electric | Commercial utility sales | Operating Segments      
Disaggregation of Revenue [Line Items]      
Revenues from contracts with customers 171,760 170,321 146,182
Electric | Industrial utility sales | Operating Segments      
Disaggregation of Revenue [Line Items]      
Revenues from contracts with customers 42,883 43,063 43,766
Electric | Other utility sales | Operating Segments      
Disaggregation of Revenue [Line Items]      
Revenues from contracts with customers 7,910 7,270 7,597
Natural gas distribution | Operating Segments      
Disaggregation of Revenue [Line Items]      
Revenues from contracts with customers 1,188,942 1,279,617 1,275,990
Other revenues 12,033 7,619 (2,402)
Total external operating revenues 1,200,975 1,287,236 1,273,588
Natural gas distribution | Intersegment eliminations      
Disaggregation of Revenue [Line Items]      
Revenues from contracts with customers (130) (301) (216)
Total external operating revenues (130) (301) (216)
Natural gas distribution | Natural gas transportation | Operating Segments      
Disaggregation of Revenue [Line Items]      
Revenues from contracts with customers 60,645 52,465 48,886
Natural gas distribution | Natural gas storage | Operating Segments      
Disaggregation of Revenue [Line Items]      
Revenues from contracts with customers 0 0 0
Natural gas distribution | Other | Operating Segments      
Disaggregation of Revenue [Line Items]      
Revenues from contracts with customers 40,703 15,141 13,617
Natural gas distribution | Residential utility sales | Operating Segments      
Disaggregation of Revenue [Line Items]      
Revenues from contracts with customers 646,049 724,600 718,191
Natural gas distribution | Commercial utility sales | Operating Segments      
Disaggregation of Revenue [Line Items]      
Revenues from contracts with customers 399,087 442,507 453,802
Natural gas distribution | Industrial utility sales | Operating Segments      
Disaggregation of Revenue [Line Items]      
Revenues from contracts with customers 42,588 45,205 41,710
Natural gas distribution | Other utility sales | Operating Segments      
Disaggregation of Revenue [Line Items]      
Revenues from contracts with customers 0 0 0
Pipeline | Operating Segments      
Disaggregation of Revenue [Line Items]      
Revenues from contracts with customers 142,230 114,892 96,439
Other revenues 367 187 256
Total external operating revenues 142,597 115,079 96,695
Pipeline | Intersegment eliminations      
Disaggregation of Revenue [Line Items]      
Revenues from contracts with customers (69,222) (62,533) (58,884)
Total external operating revenues (69,222) (62,533) (58,884)
Pipeline | Natural gas transportation | Operating Segments      
Disaggregation of Revenue [Line Items]      
Revenues from contracts with customers 174,623 145,297 129,290
Pipeline | Natural gas storage | Operating Segments      
Disaggregation of Revenue [Line Items]      
Revenues from contracts with customers 23,690 18,254 14,583
Pipeline | Other | Operating Segments      
Disaggregation of Revenue [Line Items]      
Revenues from contracts with customers 13,139 13,874 11,450
Pipeline | Residential utility sales | Operating Segments      
Disaggregation of Revenue [Line Items]      
Revenues from contracts with customers 0 0 0
Pipeline | Commercial utility sales | Operating Segments      
Disaggregation of Revenue [Line Items]      
Revenues from contracts with customers 0 0 0
Pipeline | Industrial utility sales | Operating Segments      
Disaggregation of Revenue [Line Items]      
Revenues from contracts with customers 0 0 0
Pipeline | Other utility sales | Operating Segments      
Disaggregation of Revenue [Line Items]      
Revenues from contracts with customers 0 0 0
Other | Operating Segments      
Disaggregation of Revenue [Line Items]      
Revenues from contracts with customers 0 0 0
Other revenues 0 0 0
Total external operating revenues 0 0 0
Other | Intersegment eliminations      
Disaggregation of Revenue [Line Items]      
Revenues from contracts with customers (195) (119) (86)
Total external operating revenues (195) (119) (86)
Other | Natural gas transportation | Operating Segments      
Disaggregation of Revenue [Line Items]      
Revenues from contracts with customers 0 0 0
Other | Natural gas storage | Operating Segments      
Disaggregation of Revenue [Line Items]      
Revenues from contracts with customers 0 0 0
Other | Other | Operating Segments      
Disaggregation of Revenue [Line Items]      
Revenues from contracts with customers 195 119 86
Other | Residential utility sales | Operating Segments      
Disaggregation of Revenue [Line Items]      
Revenues from contracts with customers 0 0 0
Other | Commercial utility sales | Operating Segments      
Disaggregation of Revenue [Line Items]      
Revenues from contracts with customers 0 0 0
Other | Industrial utility sales | Operating Segments      
Disaggregation of Revenue [Line Items]      
Revenues from contracts with customers 0 0 0
Other | Other utility sales | Operating Segments      
Disaggregation of Revenue [Line Items]      
Revenues from contracts with customers $ 0 $ 0 $ 0
v3.25.0.1
Revenue from Contracts with Customers - Narrative (Details)
$ in Millions
 12 Months Ended
Dec. 31, 2024
USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]  
Remaining performance obligation, amount $ 606.5
Firm Transportation Contract  
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]  
Revenue from contract with customer, term of contract 5 years
Firm Storage Contract  
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]  
Revenue from contract with customer, term of contract 1 year
Remaining performance obligation, expected timing of satisfaction, start date: 2025-01-01  
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]  
Remaining performance obligation, amount $ 82.1
Revenue, remaining performance obligation, expected timing of satisfaction, period 12 months
Remaining performance obligation, expected timing of satisfaction, start date: 2026-01-01  
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]  
Remaining performance obligation, amount $ 81.5
Revenue, remaining performance obligation, expected timing of satisfaction, period 12 months
Remaining performance obligation, expected timing of satisfaction, start date: 2027-01-01  
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]  
Remaining performance obligation, amount $ 442.9
Revenue, remaining performance obligation, expected timing of satisfaction, period
v3.25.0.1
Property, Plant and Equipment (Details) - USD ($)
$ in Thousands
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Property, plant and equipment [Line Items]      
Property, plant and equipment $ 7,554,063 $ 7,081,267 $ 6,629,518
Less accumulated depreciation and amortization 2,209,771 2,076,375 $ 1,963,260
Net property, plant and equipment 5,344,292 5,004,892  
Electric | Electric Equipment      
Property, plant and equipment [Line Items]      
Property, plant and equipment $ 1,014,906 939,474  
Weighted Average Depreciable Life in Years 49 years    
Electric | Electric Distribution      
Property, plant and equipment [Line Items]      
Property, plant and equipment $ 546,121 521,215  
Weighted Average Depreciable Life in Years 47 years    
Electric | Electric Transmission      
Property, plant and equipment [Line Items]      
Property, plant and equipment $ 662,466 639,999  
Weighted Average Depreciable Life in Years 65 years    
Electric | CWIP      
Property, plant and equipment [Line Items]      
Property, plant and equipment $ 81,316 115,103  
Electric | Other      
Property, plant and equipment [Line Items]      
Property, plant and equipment $ 176,007 153,248  
Weighted Average Depreciable Life in Years 15 years    
Natural gas distribution | CWIP      
Property, plant and equipment [Line Items]      
Property, plant and equipment $ 74,207 70,373  
Natural gas distribution | Other      
Property, plant and equipment [Line Items]      
Property, plant and equipment $ 282,007 246,991  
Weighted Average Depreciable Life in Years 15 years    
Natural gas distribution | Gas Distribution      
Property, plant and equipment [Line Items]      
Property, plant and equipment $ 2,955,435 2,771,540  
Weighted Average Depreciable Life in Years 53 years    
Natural gas distribution | Gas Transmission      
Property, plant and equipment [Line Items]      
Property, plant and equipment $ 146,710 115,057  
Weighted Average Depreciable Life in Years 56 years    
Natural gas distribution | Storage      
Property, plant and equipment [Line Items]      
Property, plant and equipment $ 43,700 42,654  
Weighted Average Depreciable Life in Years 37 years    
Natural gas distribution | General      
Property, plant and equipment [Line Items]      
Property, plant and equipment $ 229,034 215,572  
Weighted Average Depreciable Life in Years 13 years    
Pipeline | CWIP      
Property, plant and equipment [Line Items]      
Property, plant and equipment $ 29,629 57,038  
Pipeline | Other      
Property, plant and equipment [Line Items]      
Property, plant and equipment $ 73,749 68,194  
Weighted Average Depreciable Life in Years 17 years    
Pipeline | Gas Transmission      
Property, plant and equipment [Line Items]      
Property, plant and equipment $ 1,173,259 1,035,995  
Weighted Average Depreciable Life in Years 46 years    
Pipeline | Storage      
Property, plant and equipment [Line Items]      
Property, plant and equipment $ 61,369 57,160  
Weighted Average Depreciable Life in Years 53 years    
Other | Land and other      
Property, plant and equipment [Line Items]      
Property, plant and equipment $ 4,148 $ 31,654  
Weighted Average Depreciable Life in Years 7 years    
v3.25.0.1
Regulatory Assets and Liabilities - Schedule of Unamortized Regulatory Assets and Liabilities (Details) - USD ($)
$ in Thousands
Dec. 31, 2024
Dec. 31, 2023
Regulatory Asset [Abstract]    
Current regulatory assets $ 215,436 $ 172,492
Regulatory assets 322,350 447,099
Total regulatory assets 537,786 619,591
Regulatory Liability [Abstract]    
Regulatory liabilities due within one year 137,167 70,761
Regulatory liabilities 459,170 521,050
Total regulatory liabilities 596,337 591,811
Net regulatory position $ (58,551) 27,780
Environmental compliance programs    
Regulatory Liability [Abstract]    
Estimated Recovery or Refund Period 1 year  
Regulatory liabilities due within one year $ 72,387 0
Regulatory liabilities $ 0 61,941
Natural gas costs refundable through rate adjustments    
Regulatory Liability [Abstract]    
Estimated Recovery or Refund Period 1 year  
Regulatory liabilities due within one year $ 45,427 43,161
Margin sharing    
Regulatory Liability [Abstract]    
Estimated Recovery or Refund Period 1 year  
Regulatory liabilities due within one year $ 4,156 5,243
Provision for rate refund    
Regulatory Liability [Abstract]    
Estimated Recovery or Refund Period 1 year  
Regulatory liabilities due within one year $ 3,677 6,866
Taxes refundable to customers    
Regulatory Liability [Abstract]    
Estimated Recovery or Refund Period 1 year  
Regulatory liabilities due within one year $ 2,163 2,149
Regulatory liabilities $ 185,402 193,578
Conservation programs    
Regulatory Liability [Abstract]    
Estimated Recovery or Refund Period 1 year  
Regulatory liabilities due within one year $ 2,082 2,130
Cost recovery mechanisms    
Regulatory Liability [Abstract]    
Estimated Recovery or Refund Period 17 years  
Regulatory liabilities due within one year $ 1,720 6,284
Regulatory liabilities $ 30,354 21,791
Cost recovery mechanisms | Maximum    
Regulatory Liability [Abstract]    
Estimated Recovery or Refund Period 1 year  
Other    
Regulatory Liability [Abstract]    
Estimated Recovery or Refund Period 13 years  
Regulatory liabilities due within one year $ 5,555 4,928
Regulatory liabilities $ 2,161 1,809
Other | Maximum    
Regulatory Liability [Abstract]    
Estimated Recovery or Refund Period 1 year  
Plant removal and decommissioning costs    
Regulatory Liability [Abstract]    
Regulatory liabilities $ 217,603 220,147
Accumulated deferred investment tax credit    
Regulatory Liability [Abstract]    
Regulatory liabilities 18,788 15,740
Pension and postretirement benefits    
Regulatory Liability [Abstract]    
Regulatory liabilities 4,862 6,044
Natural gas costs recoverable through rate adjustments    
Regulatory Asset [Abstract]    
Current regulatory assets 91,091 98,844
Regulatory assets $ 0 55,493
Natural gas costs recoverable through rate adjustments | Minimum    
Regulatory Asset [Abstract]    
Estimated Recovery or Refund Period 1 year  
Natural gas costs recoverable through rate adjustments | Maximum    
Regulatory Asset [Abstract]    
Estimated Recovery or Refund Period 2 years  
Environmental compliance programs    
Regulatory Asset [Abstract]    
Current regulatory assets $ 76,964 5,525
Regulatory assets $ 0 66,806
Environmental compliance programs | Minimum    
Regulatory Asset [Abstract]    
Estimated Recovery or Refund Period 1 year  
Conservation programs    
Regulatory Asset [Abstract]    
Estimated Recovery or Refund Period 1 year  
Current regulatory assets $ 19,123 14,425
Electric fuel and purchased power deferral    
Regulatory Asset [Abstract]    
Current regulatory assets 9,662 33,918
Regulatory assets $ 4,349 0
Electric fuel and purchased power deferral | Minimum    
Regulatory Asset [Abstract]    
Estimated Recovery or Refund Period 1 year  
Electric fuel and purchased power deferral | Maximum    
Regulatory Asset [Abstract]    
Estimated Recovery or Refund Period 2 years  
Decoupling mechanisms    
Regulatory Asset [Abstract]    
Estimated Recovery or Refund Period 1 year  
Current regulatory assets $ 6,767 0
Cost recovery mechanisms    
Regulatory Asset [Abstract]    
Current regulatory assets 5,114 9,153
Regulatory assets $ 76,542 85,944
Cost recovery mechanisms | Minimum    
Regulatory Asset [Abstract]    
Estimated Recovery or Refund Period 1 year  
Cost recovery mechanisms | Maximum    
Regulatory Asset [Abstract]    
Estimated Recovery or Refund Period 24 years  
Other    
Regulatory Asset [Abstract]    
Estimated Recovery or Refund Period 14 years  
Current regulatory assets $ 6,715 10,627
Regulatory assets $ 5,990 6,614
Other | Minimum    
Regulatory Asset [Abstract]    
Estimated Recovery or Refund Period 1 year  
Pension and postretirement benefits    
Regulatory Asset [Abstract]    
Regulatory assets $ 142,064 142,511
Plant costs/asset retirement obligations    
Regulatory Asset [Abstract]    
Regulatory assets 47,042 46,009
Manufactured gas plant site remediation    
Regulatory Asset [Abstract]    
Regulatory assets 27,964 26,127
Taxes refundable to customers    
Regulatory Asset [Abstract]    
Regulatory assets 12,221 12,249
Covid-19 deferred costs    
Regulatory Asset [Abstract]    
Regulatory assets $ 4,167 2,746
Long-term debt refinancing costs    
Regulatory Asset [Abstract]    
Estimated Recovery or Refund Period 36 years  
Regulatory assets $ 2,011 $ 2,600
v3.25.0.1
Regulatory Assets and Liabilities - Narrative (Details) - USD ($)
$ in Millions
Dec. 31, 2024
Dec. 31, 2023
Regulatory Assets and Liabilities Disclosure [Abstract]    
Regulatory assets not earning a rate of return $ 181.2 $ 194.3
v3.25.0.1
Goodwill (Details) - USD ($)
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Goodwill [Line Items]      
Goodwill $ 345,736,000 $ 345,736,000  
Goodwill, impairment loss 0 0 $ 0
Natural gas distribution      
Goodwill [Line Items]      
Goodwill $ 345,700,000 $ 345,700,000  
v3.25.0.1
Fair Value Measurements - Narrative (Details) - USD ($)
$ in Millions
 3 Months Ended 12 Months Ended
Mar. 31, 2024
Dec. 31, 2023
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Fair Value Disclosures [Abstract]          
Investments used to satisfy nonqualified benefit plans obligations   $ 62.9 $ 59.3 $ 62.9  
Unrealized gains (losses) on investments, net of insurance proceeds     $ 5.9 $ 7.4 $ (11.2)
Investment withdrawal, reduction in cost basis $ 9.0 $ 20.0      
v3.25.0.1
Fair Value Measurements - Schedule of Available-for-Sale Securities (Details) - USD ($)
$ in Thousands
Dec. 31, 2024
Dec. 31, 2023
Debt Securities, Available-for-sale [Abstract]    
Cost $ 11,878 $ 11,755
Gross Unrealized Gains 84 45
Gross Unrealized Losses 384 478
Fair Value 11,578 11,322
Mortgage-backed securities    
Debt Securities, Available-for-sale [Abstract]    
Cost 7,933 8,234
Gross Unrealized Gains 4 17
Gross Unrealized Losses 383 470
Fair Value 7,554 7,781
U.S. Treasury securities    
Debt Securities, Available-for-sale [Abstract]    
Cost 3,945 3,521
Gross Unrealized Gains 80 28
Gross Unrealized Losses 1 8
Fair Value $ 4,024 $ 3,541
v3.25.0.1
Fair Value Measurements - Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis (Details) - USD ($)
$ in Thousands
Dec. 31, 2024
Dec. 31, 2023
Concentration Risks, Percentage [Abstract]    
Percentage in fixed-income investments 58.00% 60.00%
Percentage investment in common stock of large-cap companies 17.00% 15.00%
Percentage investment in target date investments 8.00% 8.00%
Percentage investment in common stock of mid-cap companies 8.00% 7.00%
Percentage investment in common stock of small-cap companies 4.00% 5.00%
Percentage investment in cash and cash equivalents 4.00% 3.00%
Percentage investment in high-yield investments   1.00%
Percentage investment in international investments 1.00% 1.00%
Fair Value, Recurring    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, fair value disclosure $ 83,739 $ 80,667
Fair Value, Recurring | Money market funds    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, fair value disclosure 12,879 6,409
Fair Value, Recurring | Insurance contracts    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, fair value disclosure 59,282 62,936
Fair Value, Recurring | Mortgage-backed securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, fair value disclosure 7,554 7,781
Fair Value, Recurring | U.S. Treasury securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, fair value disclosure 4,024 3,541
Quoted Prices in Active Markets for Identical Assets  (Level 1) | Fair Value, Recurring    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, fair value disclosure 0 0
Quoted Prices in Active Markets for Identical Assets  (Level 1) | Fair Value, Recurring | Money market funds    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, fair value disclosure 0 0
Quoted Prices in Active Markets for Identical Assets  (Level 1) | Fair Value, Recurring | Insurance contracts    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, fair value disclosure 0 0
Quoted Prices in Active Markets for Identical Assets  (Level 1) | Fair Value, Recurring | Mortgage-backed securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, fair value disclosure 0 0
Quoted Prices in Active Markets for Identical Assets  (Level 1) | Fair Value, Recurring | U.S. Treasury securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, fair value disclosure 0 0
Significant Other Observable Inputs  (Level 2) | Fair Value, Recurring    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, fair value disclosure 83,739 80,667
Significant Other Observable Inputs  (Level 2) | Fair Value, Recurring | Money market funds    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, fair value disclosure 12,879 6,409
Significant Other Observable Inputs  (Level 2) | Fair Value, Recurring | Insurance contracts    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, fair value disclosure 59,282 62,936
Significant Other Observable Inputs  (Level 2) | Fair Value, Recurring | Mortgage-backed securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, fair value disclosure 7,554 7,781
Significant Other Observable Inputs  (Level 2) | Fair Value, Recurring | U.S. Treasury securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, fair value disclosure 4,024 3,541
Significant Unobservable Inputs  (Level 3) | Fair Value, Recurring    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, fair value disclosure 0 0
Significant Unobservable Inputs  (Level 3) | Fair Value, Recurring | Money market funds    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, fair value disclosure 0 0
Significant Unobservable Inputs  (Level 3) | Fair Value, Recurring | Insurance contracts    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, fair value disclosure 0 0
Significant Unobservable Inputs  (Level 3) | Fair Value, Recurring | Mortgage-backed securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, fair value disclosure 0 0
Significant Unobservable Inputs  (Level 3) | Fair Value, Recurring | U.S. Treasury securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, fair value disclosure $ 0 $ 0
v3.25.0.1
Fair Value Measurements - Schedule of Fair Value, by Balance Sheet Grouping (Details) - USD ($)
$ in Thousands
Dec. 31, 2024
Dec. 31, 2023
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term debt $ 2,292,610 $ 2,166,223
Carrying Amount    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term debt 2,292,610 2,166,223
Fair Value    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term debt, fair value $ 1,963,396 $ 1,914,039
v3.25.0.1
Debt - Schedule of Credit Facilities (Details) - USD ($)
Dec. 31, 2024
Dec. 31, 2023
Line of Credit Facility [Line Items]    
Letters of credit at end of period $ 0  
Credit Agreement Expiring October 2028 | Revolving Credit Facility | Montana-Dakota Utilities Co.    
Line of Credit Facility [Line Items]    
Facility Limit 200,000,000.0  
Amount outstanding, end of period 81,400,000 $ 144,200,000
Letters of credit at end of period 0 0
Option to increase borrowings, maximum amount 250,000,000  
Credit Agreement Expiring June 2029 | Revolving Credit Facility | Cascade Natural Gas Corporation    
Line of Credit Facility [Line Items]    
Facility Limit 175,000,000.0  
Amount outstanding, end of period 64,600,000 15,400,000
Letters of credit at end of period 2,200,000  
Option to increase borrowings, maximum amount 225,000,000  
Credit Agreement Expiring June 2029 | Revolving Credit Facility | Intermountain Gas Company    
Line of Credit Facility [Line Items]    
Facility Limit 175,000,000.0  
Amount outstanding, end of period 105,100,000 30,700,000
Letters of credit at end of period 0  
Credit Agreement Expiring May 2028 | Revolving Credit Facility | MDU Resources Group, Inc.    
Line of Credit Facility [Line Items]    
Facility Limit 200,000,000.0  
Amount outstanding, end of period 0 $ 0
Letters of credit at end of period 12,100,000  
Option to increase borrowings, maximum amount $ 250,000,000  
v3.25.0.1
Debt - Short-Term Debt (Details) - USD ($)
 1 Months Ended 12 Months Ended
Jan. 19, 2024
Dec. 05, 2023
May 31, 2023
Apr. 30, 2023
Mar. 31, 2023
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Jan. 20, 2023
Short-term Debt [Line Items]                  
Short-term borrowings           $ 0 $ 95,000,000    
Repayment of short-term borrowings           $ 95,000,000 433,901,000 $ 0  
MDU Resources Group, Inc. | Revolving Credit Facility                  
Short-term Debt [Line Items]                  
Short-term borrowings     $ 150,000,000       $ 0    
Term Loan Agreement | Cascade Natural Gas                  
Short-term Debt [Line Items]                  
Short-term borrowings                 $ 150,000,000
Repayment of short-term borrowings $ 50,000,000 $ 100,000,000              
Term Loan Agreement | Intermountain Gas Company                  
Short-term Debt [Line Items]                  
Short-term borrowings                 $ 125,000,000
Repayment of short-term borrowings $ 45,000,000   $ 30,000,000 $ 30,000,000 $ 20,000,000        
v3.25.0.1
Debt - Schedule of Long-Term Debt Outstanding (Details) - USD ($)
$ in Thousands
Dec. 31, 2024
Dec. 31, 2023
Long-term debt outstanding [Line Items]    
Less unamortized debt issuance costs $ 6,436 $ 6,357
Total long-term debt 2,292,610 2,166,223
Less current maturities 161,700 61,319
Net long-term debt $ 2,130,910 2,104,904
Senior Notes    
Long-term debt outstanding [Line Items]    
Weighted average interest rate 4.57%  
Long-term debt, gross $ 1,947,000 1,882,000
Line of Credit    
Long-term debt outstanding [Line Items]    
Weighted average interest rate 5.79%  
Long-term debt, gross $ 169,700 46,100
Commercial paper    
Long-term debt outstanding [Line Items]    
Weighted average interest rate 4.76%  
Long-term debt, gross $ 81,400 144,200
Term Loan Agreements    
Long-term debt outstanding [Line Items]    
Weighted average interest rate 4.44%  
Long-term debt, gross $ 65,600 64,300
Medium-term notes    
Long-term debt outstanding [Line Items]    
Weighted average interest rate 7.32%  
Long-term debt, gross $ 35,000 35,000
Other notes    
Long-term debt outstanding [Line Items]    
Weighted average interest rate 6.00%  
Long-term debt, gross $ 346 $ 980
v3.25.0.1
Debt - Long-Term Debt (Details)
$ in Thousands
 12 Months Ended
Nov. 01, 2024
USD ($)
Nov. 15, 2023
USD ($)
Dec. 31, 2024
USD ($)
Dec. 31, 2023
USD ($)
Dec. 31, 2022
USD ($)
Jul. 11, 2024
USD ($)
Jun. 20, 2024
USD ($)
Jun. 19, 2024
USD ($)
Apr. 01, 2024
USD ($)
Oct. 18, 2023
USD ($)
May 31, 2023
USD ($)
Long-term debt outstanding [Line Items]                      
Long-term debt     $ 2,292,610 $ 2,166,223              
Repayments of long-term debt     $ 182,135 568,883 $ 38,764            
Montana-Dakota Utilities Co.                      
Long-term debt outstanding [Line Items]                      
Ratio of total debt to total capitalization     0.48                
Revolving Credit Facility | Montana-Dakota Utilities Co.                      
Long-term debt outstanding [Line Items]                      
Line of credit facility, maximum borrowing capacity                   $ 200,000  
Ratio of funded debt to total capitalization as specified in debt covenants     0.65                
Revolving Credit Facility | Cascade Natural Gas                      
Long-term debt outstanding [Line Items]                      
Ratio of total debt to total capitalization     0.65                
Revolving Credit Facility | Intermountain Gas Company                      
Long-term debt outstanding [Line Items]                      
Ratio of total debt to total capitalization     0.65                
Revolving Credit Facility | MDU Resources Group, Inc.                      
Long-term debt outstanding [Line Items]                      
Long-term debt                     $ 200,000
Ratio of total debt to total capitalization     0.65                
Senior Notes                      
Long-term debt outstanding [Line Items]                      
Long-term debt, gross     $ 1,947,000 $ 1,882,000              
Senior Notes | Montana-Dakota Utilities Co.                      
Long-term debt outstanding [Line Items]                      
Ratio of funded debt to total capitalization as specified in debt covenants           0.65          
Long-term debt           $ 125,000          
Interest rate, stated percentage           5.96%          
Senior Notes | Cascade Natural Gas                      
Long-term debt outstanding [Line Items]                      
Total debt to total capitalization     0.50                
Senior Notes | Intermountain Gas Company                      
Long-term debt outstanding [Line Items]                      
Total debt to total capitalization     0.60                
Senior Notes | MDU Resources Group, Inc.                      
Long-term debt outstanding [Line Items]                      
Total debt to total capitalization     0.46                
Revolving Credit Agreement | Cascade Natural Gas                      
Long-term debt outstanding [Line Items]                      
Line of credit facility, maximum borrowing capacity             $ 175,000 $ 100,000      
Revolving Credit Agreement | Intermountain Gas Company                      
Long-term debt outstanding [Line Items]                      
Line of credit facility, maximum borrowing capacity             $ 175,000 $ 100,000      
Term Loan Agreement | MDU Resources Group, Inc.                      
Long-term debt outstanding [Line Items]                      
Long-term debt                     $ 375,000
Repayments of long-term debt $ 190,000 $ 185,000                  
Term Loan Agreement | WBI Energy Transmission                      
Long-term debt outstanding [Line Items]                      
Long-term debt                 $ 60,000    
Interest rate, stated percentage                 4.52%    
Ratio of total debt to total capitalization                 0.65    
Debt instrument, annual principal payment                 $ 4,000    
Uncommitted Note Purchase And Private Shelf Agreement | WBI Energy Transmission                      
Long-term debt outstanding [Line Items]                      
Line of credit facility, maximum borrowing capacity     $ 350,000                
Ratio of total debt to total capitalization     0.55                
Total debt to total capitalization     0.40                
Long-term debt, gross     $ 235,000                
Line of credit facility, remaining borrowing capacity     $ 115,000                
v3.25.0.1
Debt - Schedule of Debt Maturities (Details)
$ in Thousands
Dec. 31, 2024
USD ($)
Debt Disclosure [Abstract]  
2025 $ 161,700
2026 144,700
2027 24,700
2028 161,100
2029 244,400
Thereafter $ 1,562,446
v3.25.0.1
Asset Retirement Obligations (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]    
Balance at beginning of year $ 385,154 $ 373,147
Liabilities incurred 2,721 533
Liabilities settled (5,271) (6,633)
Accretion expense 19,655 18,894
Revisions in estimates 4,388 (787)
Balance at end of year 406,647 385,154
Plant costs/asset retirement obligations    
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]    
Accretion expense, including asset retirement obligations $ 19,600 $ 18,900
v3.25.0.1
Equity (Details)
$ / shares in Units, $ in Thousands
 12 Months Ended
Dec. 31, 2024
USD ($)
$ / shares
shares
Dec. 31, 2023
USD ($)
$ / shares
shares
Dec. 31, 2022
USD ($)
$ / shares
Class of Stock [Line Items]      
Number of years dividends have been paid 87 years    
Dividends declared per common share (in usd per share) | $ / shares $ 0.5100 $ 0.6950 $ 0.8750
Dividends declared on common stock | $ $ 104,786 $ 142,033 $ 178,761
Credit agreement limitation on company's subsidiaries ratio of funded debt to capitalization 0.65    
Company's subsidiaries net assets restricted from use for dividend payments | $ $ 1,300,000    
Common Stock      
Class of Stock [Line Items]      
Dividends declared on common stock | $ $ 103,900 $ 141,500 $ 177,900
K-Plan      
Class of Stock [Line Items]      
Common stock, authorized shares remaining (in shares) | shares 7,200,000    
Preferred Stock      
Class of Stock [Line Items]      
Preferred stock, authorized (in shares) | shares 2,000,000    
Preferred stock, par value per share (in usd per share) | $ / shares $ 100    
Preferred stock, outstanding (in shares) | shares 0 0  
v3.25.0.1
Stock-Based Compensation - Narrative (Details) - USD ($)
$ / shares in Units, $ in Thousands
 10 Months Ended 12 Months Ended
Oct. 30, 2024
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Share-based compensation arrangement by share-based payment award [Line Items]        
Share-based compensation arrangement, number of shares available for grant (in shares)   2,300,000    
Share-based compensation expense, net of tax   $ 7,100 $ 5,100 $ 6,900
Share-based compensation nonvested awards total compensation cost not yet recognized   $ 8,400    
Share-based compensation, nonvested awards, total compensation cost not yet recognized, period for recognition   1 year 3 months 18 days    
RSUs        
Share-based compensation arrangement by share-based payment award [Line Items]        
Award vesting period   3 years    
Share-based payment arrangement, plan modification, incremental cost   $ 1,700    
Share-based payment arrangement, plan modification, incremental cost, recognized   $ 854    
Weighted average grant-date fair value (in usd per share) $ 20.89      
Share-Based Payment Arrangement        
Share-based compensation arrangement by share-based payment award [Line Items]        
Share-based compensation arrangement shares issued in period (in shares)   46,341 50,717 40,800
Share-based compensation arrangement, fair value   $ 850 $ 950 $ 1,200
Performance Shares        
Share-based compensation arrangement by share-based payment award [Line Items]        
Award vesting period     3 years  
Fair value of vested shares       $ 7,600
Performance Shares | Market Condition        
Share-based compensation arrangement by share-based payment award [Line Items]        
Historical volatility rate   50.00%    
Implied volatility rate   50.00%    
Weighted average grant-date fair value (in usd per share)       $ 36.25
Performance Shares | Market Condition | Minimum        
Share-based compensation arrangement by share-based payment award [Line Items]        
Participant target grant of shares, percentage rate range   0.00%    
Performance Shares | Market Condition | Maximum        
Share-based compensation arrangement by share-based payment award [Line Items]        
Participant target grant of shares, percentage rate range   200.00%    
Performance Shares | Performance Condition        
Share-based compensation arrangement by share-based payment award [Line Items]        
Weighted average grant-date fair value (in usd per share)       $ 27.73
Performance Shares | Performance Condition | Minimum        
Share-based compensation arrangement by share-based payment award [Line Items]        
Participant target grant of shares, percentage rate range   0.00%    
Performance Shares | Performance Condition | Maximum        
Share-based compensation arrangement by share-based payment award [Line Items]        
Participant target grant of shares, percentage rate range   200.00%    
v3.25.0.1
Stock-Based Compensation - Schedule of Target Grants of Restricted Stock Units (Details) - RSUs
Dec. 31, 2024
shares
Grant Date February 2023 July 2023  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Target grant of shares (in shares) 542,233
Grant Date February 2024 June 2024  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Target grant of shares (in shares) 698,284
v3.25.0.1
Stock-Based Compensation - Schedule of Restricted Stock Unit and Performance Share Awards Activity (Details) - RSUs - $ / shares
 2 Months Ended 10 Months Ended
Dec. 31, 2024
Oct. 30, 2024
Number of Shares    
Nonvested at beginning of period (in shares) 1,239,412 873,300
Granted pre-separation of Everus (in shares)   478,938
Forfeited (in shares)   (112,826)
Adjustments for performance (in shares) 663,661  
Vested (in shares) (662,556)  
Nonvested at end of period (in shares) 1,240,517  
Weighted Average Grant-Date Fair Value    
Weighted Average Grant Date Fair Value, Nonvested at beginning of period (in usd per share)   $ 21.16
Weighted Average Grant Date Fair Value, Granted (in usd per share)   20.89
Weighted Average Grant Date Fair Value, Forfeited (in usd per share)   $ 21.35
Weighted Average Grant Date Fair Value, Vested (in usd per share) $ 12.04  
Weighted Average Grant Date Fair Value, Nonvested at end of period (in usd per share) $ 12.56  
v3.25.0.1
Stock-Based Compensation - Schedule of Performance Shares Valuation Assumptions (Details) - Market Condition - Performance Shares
 12 Months Ended
Dec. 31, 2022
$ / shares
Share-based compensation arrangement by share-based payment award [Line Items]  
Weighted average grant-date fair value (in usd per share) $ 36.25
Blended volatility rate, minimum 24.07%
Blended volatility rate, maximum 31.41%
Risk-free interest rate, minimum 0.71%
Risk-free interest rate, maximum 1.68%
Weighted average discounted dividends per share (in usd per share) $ 2.93
v3.25.0.1
Accumulated Other Comprehensive Loss - Schedule of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
AOCI Attributable to Parent, Net of Tax [Roll Forward]    
Beginning balance $ 2,905,233 $ 3,587,129
Other comprehensive income (loss) before reclassifications 1,134 (473)
Amounts reclassified from accumulated other comprehensive loss 452 366
Other comprehensive income (loss) 1,586 (107)
Ending balance 2,690,574 2,905,233
Discontinued Operations, Disposed of by Means Other than Sale, Spinoff | Knife River Corporation    
AOCI Attributable to Parent, Net of Tax [Roll Forward]    
Amounts reclassified from accumulated other comprehensive loss   12,306
Total Accumulated Other Comprehensive Loss    
AOCI Attributable to Parent, Net of Tax [Roll Forward]    
Beginning balance (18,384) (30,583)
Ending balance (16,798) (18,384)
Net Unrealized Loss on Derivative Instruments Qualifying as Hedges    
AOCI Attributable to Parent, Net of Tax [Roll Forward]    
Beginning balance 0 (125)
Other comprehensive income (loss) before reclassifications 0 0
Amounts reclassified from accumulated other comprehensive loss 0 81
Other comprehensive income (loss) 0 81
Ending balance 0 0
Net Unrealized Loss on Derivative Instruments Qualifying as Hedges | Discontinued Operations, Disposed of by Means Other than Sale, Spinoff | Knife River Corporation    
AOCI Attributable to Parent, Net of Tax [Roll Forward]    
Amounts reclassified from accumulated other comprehensive loss   44
Postretirement Liability Adjustment    
AOCI Attributable to Parent, Net of Tax [Roll Forward]    
Beginning balance (18,042) (29,900)
Other comprehensive income (loss) before reclassifications 1,049 (646)
Amounts reclassified from accumulated other comprehensive loss 432 242
Other comprehensive income (loss) 1,481 (404)
Ending balance (16,561) (18,042)
Postretirement Liability Adjustment | Discontinued Operations, Disposed of by Means Other than Sale, Spinoff | Knife River Corporation    
AOCI Attributable to Parent, Net of Tax [Roll Forward]    
Amounts reclassified from accumulated other comprehensive loss   12,262
Net Unrealized Gain (Loss) on Available- for-sale Investments    
AOCI Attributable to Parent, Net of Tax [Roll Forward]    
Beginning balance (342) (558)
Other comprehensive income (loss) before reclassifications 85 173
Amounts reclassified from accumulated other comprehensive loss 20 43
Other comprehensive income (loss) 105 216
Ending balance $ (237) (342)
Net Unrealized Gain (Loss) on Available- for-sale Investments | Discontinued Operations, Disposed of by Means Other than Sale, Spinoff | Knife River Corporation    
AOCI Attributable to Parent, Net of Tax [Roll Forward]    
Amounts reclassified from accumulated other comprehensive loss   $ 0
v3.25.0.1
Accumulated Other Comprehensive Loss - Schedule of Reclassification Out of AOCI (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Reclassification Adjustment out of Accumulated Other Comprehensive Loss [Line Items]      
Interest expense $ (108,347) $ (104,624) $ (80,683)
Income taxes 17,589 10,213 6,195
Other income 41,367 33,454 3,260
Net income 281,108 414,707 $ 367,489
Reclassification out of Accumulated Other Comprehensive Income      
Reclassification Adjustment out of Accumulated Other Comprehensive Loss [Line Items]      
Net income (452) (366)  
Reclassification adjustment for loss on derivative instruments included in net income | Reclassification out of Accumulated Other Comprehensive Income | Interest Rate Contract      
Reclassification Adjustment out of Accumulated Other Comprehensive Loss [Line Items]      
Interest expense 0 (96)  
Income taxes 0 15  
Net income 0 (81)  
Amortization of postretirement liability losses included in net periodic benefit credit | Reclassification out of Accumulated Other Comprehensive Income      
Reclassification Adjustment out of Accumulated Other Comprehensive Loss [Line Items]      
Income taxes 145 78  
Other income 577 320  
Net income (432) (242)  
Reclassification adjustment on available-for-sale investments included in net income | Reclassification out of Accumulated Other Comprehensive Income      
Reclassification Adjustment out of Accumulated Other Comprehensive Loss [Line Items]      
Income taxes 5 11  
Other income 25 54  
Net income $ (20) $ (43)  
v3.25.0.1
Income Taxes - Schedule of Components of Income Before Income Taxes from Continuing Operations (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Income Tax Disclosure [Abstract]      
United States $ 198,662 $ 340,330 $ 123,447
Income before income taxes $ 198,662 $ 340,330 $ 123,447
v3.25.0.1
Income Taxes - Schedule of Income Tax Expense (Benefit) (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Current:      
Federal $ 30,412 $ 8,271 $ (15,849)
State 3,255 3,251 1,857
Current income taxes 33,667 11,522 (13,992)
Deferred:      
Federal (17,321) (3,331) 15,038
State (1,805) (125) 4,251
Investment tax credit - net 3,048 2,147 898
Deferred income taxes (16,078) (1,309) 20,187
Income taxes $ 17,589 $ 10,213 $ 6,195
v3.25.0.1
Income Taxes - Schedule of Components of Deferred Tax Assets and Liabilities (Details) - USD ($)
$ in Thousands
Dec. 31, 2024
Dec. 31, 2023
Deferred tax assets:    
Environmental compliance $ 33,730 $ 28,873
Pension and postretirement 25,508 27,584
Compensation-related 15,651 17,106
Customer advances 9,719 8,312
Cost recovery mechanisms 7,402 5,314
Legal and environmental contingencies 5,317 4,881
Other 20,386 13,045
Total deferred tax assets 117,713 105,115
Deferred tax liabilities:    
Basis differences on property, plant and equipment 426,493 404,039
Pension and postretirement 48,355 39,110
Purchased gas adjustment 20,441 34,618
Environmental compliance 17,260 16,221
Cost recovery mechanisms 19,245 22,604
Legal and environmental contingencies 6,300 5,902
Other 19,931 33,947
Total deferred tax liabilities 558,025 556,441
Valuation allowance 1,008 1,010
Net deferred income tax liability $ 441,320 $ 452,336
v3.25.0.1
Income Taxes - Narrative (Details) - State and local jurisdiction - USD ($)
$ in Millions
Dec. 31, 2024
Dec. 31, 2023
Carryforwards [Line Items]    
Operating loss carryforwards $ 1.0 $ 1.0
Tax credit carryforward, amount $ 31.6 $ 33.7
v3.25.0.1
Income Taxes - Schedule of Deferred Tax Reconciliation (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Income Tax Disclosure [Abstract]      
Change in net deferred income tax liability from the preceding table $ (11,016)    
Excess deferred income tax amortization (8,121)    
Deferred taxes associated with other comprehensive income (532)    
Other 3,591    
Deferred income taxes $ (16,078) $ (1,309) $ 20,187
v3.25.0.1
Income Taxes - Schedule of Income Tax Expense (Benefit) Statutory Rate vs Actual Rate (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Computed tax at federal statutory rate      
Computed tax at federal statutory rate $ 41,719 $ 71,469 $ 25,924
Federal statutory rate 21.00% 21.00% 21.00%
Increases (reductions) resulting from:      
State income taxes, net of federal income tax $ 4,047 $ 3,605 $ 2,484
State income taxes, net of federal income tax, rate 2.00% 1.10% 2.00%
State investment tax credit, net of federal income tax $ 2,400 $ 1,545 $ 1,624
State investment tax credit, net of federal income tax, rate 1.20% 0.50% 1.30%
Executive compensation $ 2,111 $ 564 $ 683
Executive compensation, rate 1.10% 0.20% 0.60%
Federal renewable energy credit $ (16,871) $ (15,175) $ (15,343)
Federal renewable energy credit, rate (8.50%) (4.50%) (12.40%)
Excess deferred income tax amortization $ (8,121) $ (8,383) $ (9,008)
Excess deferred income tax amortization, rate (4.10%) (2.50%) (7.30%)
State tax rate change $ (2,317) $ (9) $ (3)
State tax rate change, rate (1.20%) 0.00% 0.00%
Research and development tax credit $ (1,465) $ (1,985) $ (1,692)
Research and development tax credit, rate (0.70%) (0.60%) (1.40%)
Nonqualified benefit plans $ (1,142) $ (1,313) $ 1,516
Nonqualified benefit plans, rate (0.60%) (0.40%) 1.20%
Tax-free debt for equity exchange $ 0 $ (38,967) $ 0
Tax-free debt for equity exchange, rate 0.00% (11.40%) 0.00%
Other $ (2,772) $ (1,138) $ 10
Other, rate (1.40%) (0.30%) 0.00%
Income taxes $ 17,589 $ 10,213 $ 6,195
Total income tax expense, rate 8.80% 3.10% 5.00%
v3.25.0.1
Cash Flow Information (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Supplemental Cash Flow Information [Line Items]      
Interest, net $ 108,242 $ 112,839 $ 49,036
Income taxes paid, net 43,572 12,162 (27,884)
AFUDC borrowed 11,000 10,000 2,200
Property, plant and equipment additions in accounts payable 36,820 46,364 34,886
Right-of-use assets obtained in exchange for new operating lease liabilities 1,787 2,265 1,324
Debt for equity exchange of retained shares in Knife River 0 293,239 0
Continuing And Discontinued Operations      
Supplemental Cash Flow Information [Line Items]      
Income taxes paid, net $ 80,900 $ 62,500 $ 26,400
v3.25.0.1
Business Segment Data - Schedule of Segment Reporting Information, by Segment (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Business segment data [Line Items]      
External operating revenues $ 1,757,978 $ 1,803,352 $ 1,747,298
External operation and maintenance 414,491 407,081 379,951
Purchased natural gas sold 630,403 742,965 757,883
Electric fuel and purchased power 141,148 134,779 119,405
Depreciation and amortization 200,078 190,450 188,560
Taxes, other than income 106,216 103,133 100,629
Realized gain on tax-free exchange of the retained shares in Knife River 0 186,556 0
Other income (41,367) (33,454) (3,260)
Interest expense 108,347 104,624 80,683
Income tax expense (benefit) 17,589 10,213 6,195
Income (loss) from continuing operations 181,073 330,117 117,252
Discontinued operations, net of tax 100,035 84,590 250,237
Net income 281,108 414,707 367,489
Capital expenditures 525,498 497,719 438,229
Assets 7,038,818 7,833,159 9,660,781
Property, plant and equipment 7,554,063 7,081,267 6,629,518
Accumulated depreciation and amortization 2,209,771 2,076,375 1,963,260
Additional information [Abstract]      
Net noncash acquisitions, capital expenditure-related accounts payable and AFUDC 7,100 (13,600) 4,400
Operating Segments      
Business segment data [Line Items]      
External operating revenues 1,827,402 1,866,324 1,806,456
Assets 6,892,959 6,564,962 6,061,151
Operating Segments | Electric      
Business segment data [Line Items]      
External operating revenues 414,406 401,037 377,015
External operation and maintenance 94,897 92,521 93,236
Purchased natural gas sold 0 0 0
Electric fuel and purchased power 141,148 134,779 119,405
Depreciation and amortization 66,524 64,253 67,802
Taxes, other than income 17,605 16,695 16,917
Realized gain on tax-free exchange of the retained shares in Knife River   0  
Other income (8,205) (5,815) (528)
Interest expense 30,058 28,064 28,526
Income tax expense (benefit) (2,414) (1,019) (5,420)
Income (loss) from continuing operations 74,793 71,559 57,077
Discontinued operations, net of tax 0 0 0
Net income 74,793 71,559 57,077
Capital expenditures 110,812 109,805 133,970
Assets 1,976,912 1,955,644 1,856,258
Property, plant and equipment 2,480,816 2,369,039 2,276,613
Accumulated depreciation and amortization 716,736 660,438 625,813
Operating Segments | Natural gas distribution      
Business segment data [Line Items]      
External operating revenues 1,200,975 1,287,236 1,273,588
External operation and maintenance 231,087 219,481 205,009
Purchased natural gas sold 630,403 742,965 757,883
Electric fuel and purchased power 0 0 0
Depreciation and amortization 101,958 95,300 89,466
Taxes, other than income 76,042 75,207 71,095
Realized gain on tax-free exchange of the retained shares in Knife River   0  
Other income (25,509) (20,867) (3,213)
Interest expense 63,185 57,601 42,126
Income tax expense (benefit) 7,974 6,927 7,805
Income (loss) from continuing operations 46,937 48,520 45,171
Discontinued operations, net of tax 0 0 0
Net income 46,937 48,520 45,171
Capital expenditures 286,152 274,836 240,064
Assets 3,730,532 3,532,142 3,214,452
Property, plant and equipment 3,731,093 3,462,187 3,208,059
Accumulated depreciation and amortization 1,139,223 1,068,037 1,009,788
Operating Segments | Pipeline      
Business segment data [Line Items]      
External operating revenues 142,597 115,079 96,695
External operation and maintenance 75,456 70,386 60,300
Purchased natural gas sold 0 0 0
Electric fuel and purchased power 0 0 0
Depreciation and amortization 29,362 26,811 26,857
Taxes, other than income 12,175 10,822 12,318
Realized gain on tax-free exchange of the retained shares in Knife River   0  
Other income (5,850) (3,675) (1,272)
Interest expense 10,862 9,428 9,966
Income tax expense (benefit) 17,470 12,409 10,522
Income (loss) from continuing operations 68,042 47,375 36,194
Discontinued operations, net of tax 0 (457) (906)
Net income 68,042 46,918 35,288
Capital expenditures 126,806 115,903 61,923
Assets 1,151,317 1,045,704 961,893
Property, plant and equipment 1,338,006 1,218,387 1,108,141
Accumulated depreciation and amortization 351,045 328,010 308,516
Operating Segments | Other      
Business segment data [Line Items]      
External operating revenues 0 0 0
External operation and maintenance 13,051 24,693 21,406
Purchased natural gas sold 0 0 0
Electric fuel and purchased power 0 0 0
Depreciation and amortization 2,234 4,086 4,435
Taxes, other than income 394 409 299
Other income (1,803) (3,097) 1,753
Interest expense 4,242 9,531 65
Income tax expense (benefit) (5,441) (8,104) (6,712)
Income (loss) from continuing operations (8,699) 162,663 (21,190)
Discontinued operations, net of tax 100,035 85,047 251,143
Net income 91,336 247,710 229,953
Capital expenditures 1,728 (2,825) 2,272
Assets 180,057 1,299,669 3,628,178
Property, plant and equipment 4,148 31,654 36,705
Accumulated depreciation and amortization 2,767 19,890 19,143
Intersegment eliminations      
Business segment data [Line Items]      
External operating revenues (69,619) (63,091) (59,244)
External operation and maintenance (721) (989) (998)
Purchased natural gas sold (68,898) (62,102) (58,246)
Other income 15,453 13,648 636
Interest expense (15,453) (13,648) (636)
Assets (379,399) (579,235) (1,184,512)
Intersegment eliminations | Electric      
Business segment data [Line Items]      
External operating revenues (72) (138) (58)
External operation and maintenance (72) (138) (58)
Purchased natural gas sold 0 0 0
Other income 0 0 0
Interest expense 0 0 0
Intersegment eliminations | Natural gas distribution      
Business segment data [Line Items]      
External operating revenues (130) (301) (216)
External operation and maintenance (130) (301) (216)
Purchased natural gas sold (68,898) (62,102) (58,246)
Other income 0 0 0
Interest expense 0 0 0
Intersegment eliminations | Pipeline      
Business segment data [Line Items]      
External operating revenues (69,222) (62,533) (58,884)
External operation and maintenance (324) (431) (638)
Purchased natural gas sold 0 0 0
Other income 655 217 80
Interest expense (4,633) (3,842) (136)
Intersegment eliminations | Other      
Business segment data [Line Items]      
External operating revenues (195) (119) (86)
External operation and maintenance (195) (119) (86)
Purchased natural gas sold 0 0 0
Other income 14,798 13,431 556
Interest expense $ (10,820) $ (9,806) $ (500)
v3.25.0.1
Business Segment Data - Schedule of Operating Revenues and Operating Assets Reconciliation (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Segment Reporting, Revenue Reconciling Item [Line Items]      
External operating revenues $ 1,757,978 $ 1,803,352 $ 1,747,298
Assets 7,038,818 7,833,159 9,660,781
Operating Segments      
Segment Reporting, Revenue Reconciling Item [Line Items]      
External operating revenues 1,827,402 1,866,324 1,806,456
Assets 6,892,959 6,564,962 6,061,151
Other      
Segment Reporting, Revenue Reconciling Item [Line Items]      
External operating revenues 195 119 86
Assets 525,258 1,847,432 4,784,142
Intersegment eliminations      
Segment Reporting, Revenue Reconciling Item [Line Items]      
External operating revenues (69,619) (63,091) (59,244)
Assets $ (379,399) $ (579,235) $ (1,184,512)
v3.25.0.1
Employee Benefit Plans - Change in Benefit Obligations and Plan Assets (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Pension Benefits      
Change in benefit obligation:      
Benefit obligation at beginning of year $ 275,586 $ 278,286  
Service cost 0 0 $ 0
Interest cost 12,799 13,521 9,396
Plan participants' contributions 0 0  
Actuarial (gain) loss (11,040) 5,395  
Benefits paid (21,995) (21,616)  
Benefit obligation at end of year 255,350 275,586 278,286
Change in net plan assets:      
Fair value of plan assets at beginning of year 248,558 242,031  
Actual return on plan assets 1,152 20,576  
Employer contribution 2,911 7,567  
Plan participants' contributions 0 0  
Benefits paid (21,995) (21,616)  
Fair value of net plan assets at end of year 230,626 248,558 242,031
Funded status - (under) over (24,724) (27,028)  
Amounts recognized in the Consolidated Balance Sheets at December 31:      
Noncurrent assets - other 0 0  
Noncurrent liabilities - other 24,724 27,028  
Benefit obligation (liabilities) assets - net amount recognized (24,724) (27,028)  
Amounts recognized in accumulated other comprehensive loss:      
Actuarial loss (gain) 13,228 32,273  
Prior service credit 0 0  
Total 13,228 32,273  
Amounts recognized in regulatory assets or liabilities:      
Actuarial loss (gain) 139,962 140,232  
Prior service credit 0 0  
Total 139,962 140,232  
Other Postretirement Benefits      
Change in benefit obligation:      
Benefit obligation at beginning of year 39,590 40,315  
Service cost 505 534 894
Interest cost 1,837 1,956 1,383
Plan participants' contributions 412 479  
Actuarial (gain) loss (3,420) (215)  
Benefits paid (3,249) (3,479)  
Benefit obligation at end of year 35,675 39,590 40,315
Change in net plan assets:      
Fair value of plan assets at beginning of year 79,234 76,640  
Actual return on plan assets 2,297 5,518  
Employer contribution 71 76  
Plan participants' contributions 412 479  
Benefits paid (3,249) (3,479)  
Fair value of net plan assets at end of year 78,765 79,234 $ 76,640
Funded status - (under) over 43,090 39,644  
Amounts recognized in the Consolidated Balance Sheets at December 31:      
Noncurrent assets - other 43,090 39,644  
Noncurrent liabilities - other 0 0  
Benefit obligation (liabilities) assets - net amount recognized 43,090 39,644  
Amounts recognized in accumulated other comprehensive loss:      
Actuarial loss (gain) (809) (3,515)  
Prior service credit (37) (115)  
Total (846) (3,630)  
Amounts recognized in regulatory assets or liabilities:      
Actuarial loss (gain) (1,478) (1,146)  
Prior service credit (1,303) (2,619)  
Total $ (2,781) $ (3,765)  
v3.25.0.1
Employee Benefit Plans - Benefit Obligations in Excess of Plan Assets (Details) - Pension Benefits - USD ($)
$ in Thousands
Dec. 31, 2024
Dec. 31, 2023
Defined Benefit Plan Disclosure [Line Items]    
Projected benefit obligation $ 255,350 $ 275,586
Accumulated benefit obligation 255,350 275,586
Fair value of plan assets $ 230,626 $ 248,558
v3.25.0.1
Employee Benefit Plans - Components of Net Periodic Benefit Cost (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Pension Benefits      
Components of net periodic benefit cost (credit):      
Service cost $ 0 $ 0 $ 0
Interest cost 12,799 13,521 9,396
Expected return on assets (16,113) (17,194) (17,482)
Amortization of prior service credit 0 0 0
Recognized net actuarial loss (gain) 4,149 3,093 5,826
Net periodic benefit cost (credit), including amount capitalized 835 (580) (2,260)
Less amount capitalized 0 0 0
Net periodic benefit cost 835 (580) (2,260)
Other changes in plan assets and benefit obligations recognized in accumulated comprehensive loss:      
Net loss (gain) 401 187 2,369
Amortization of actuarial (loss) gain (359) (292) (1,310)
Amortization of prior service credit 0 0 0
Reclassification of postretirement liability adjustment from regulatory asset 0 0 5,343
Total recognized in accumulated other comprehensive loss 42 (105) 6,402
Other changes in plan assets and benefit obligations recognized in regulatory assets or liabilities:      
Net loss (gain) 3,520 1,826 9,757
Amortization of actuarial (loss) gain (3,790) (2,801) (5,373)
Amortization of prior service credit 0 0 0
Reclassification of postretirement liability adjustment from regulatory asset 0 0 (5,343)
Total recognized in regulatory assets or liabilities (270) (975) (959)
Total recognized in net periodic benefit credit, accumulated other comprehensive loss and regulatory assets or liabilities 607 (1,660) 3,183
Other Postretirement Benefits      
Components of net periodic benefit cost (credit):      
Service cost 505 534 894
Interest cost 1,837 1,956 1,383
Expected return on assets (5,315) (5,361) (5,277)
Amortization of prior service credit (1,318) (1,318) (1,318)
Recognized net actuarial loss (gain) (288) (504) (570)
Net periodic benefit cost (credit), including amount capitalized (4,579) (4,693) (4,888)
Less amount capitalized 0 107 175
Net periodic benefit cost (4,579) (4,800) (5,063)
Other changes in plan assets and benefit obligations recognized in accumulated comprehensive loss:      
Net loss (gain) 71 (604) (4,141)
Amortization of actuarial (loss) gain 130 108 (281)
Amortization of prior service credit 45 78 125
Reclassification of postretirement liability adjustment from regulatory asset 0 0 (992)
Total recognized in accumulated other comprehensive loss 246 (418) (5,289)
Other changes in plan assets and benefit obligations recognized in regulatory assets or liabilities:      
Net loss (gain) (472) (107) 11,920
Amortization of actuarial (loss) gain 158 304 500
Amortization of prior service credit 1,273 1,273 1,273
Reclassification of postretirement liability adjustment from regulatory asset 0 0 992
Total recognized in regulatory assets or liabilities 959 1,470 14,685
Total recognized in net periodic benefit credit, accumulated other comprehensive loss and regulatory assets or liabilities $ (3,374) $ (3,748) $ 4,333
v3.25.0.1
Employee Benefit Plans - Weighted Average Assumptions (Details)
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Pension Benefits    
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]    
Discount rate 5.41% 4.84%
Expected return on plan assets 6.50% 6.50%
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]    
Discount rate 4.84% 5.06%
Expected return on plan assets 6.50% 6.50%
Other Postretirement Benefits    
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]    
Discount rate 5.43% 4.85%
Expected return on plan assets 6.00% 6.00%
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]    
Discount rate 4.85% 5.07%
Expected return on plan assets 6.00% 6.00%
v3.25.0.1
Employee Benefit Plans - Narrative (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Defined Benefit Plan Disclosure [Line Items]      
Nonqualified defined contribution plan, cost $ 4,000 $ 2,700 $ 538
Defined Contribution Plan      
Defined Benefit Plan Disclosure [Line Items]      
Nonqualified defined contribution plan, cost 10,700 $ 17,000 $ 14,300
Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Expected future employer contributions, next fiscal year 1,700    
Other Postretirement Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Expected future employer contributions, next fiscal year $ 18    
Minimum      
Defined Benefit Plan Disclosure [Line Items]      
Multiemployer plan yellow zone status funded percentage 65.00%    
Multiemployer plan green zone status funded percentage 80.00%    
Minimum | Equity securities | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Defined benefit plan, plan assets, target allocation, percentage 40.00%    
Minimum | Equity securities | Other Postretirement Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Defined benefit plan, plan assets, target allocation, percentage 10.00%    
Minimum | Fixed Income Securities | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Defined benefit plan, plan assets, target allocation, percentage 50.00%    
Minimum | Fixed Income Securities | Other Postretirement Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Defined benefit plan, plan assets, target allocation, percentage 80.00%    
Maximum      
Defined Benefit Plan Disclosure [Line Items]      
Multiemployer plan red zone status funded percentage 65.00%    
Multiemployer plan yellow status funded percentage 80.00%    
Maximum | Equity securities | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Defined benefit plan, plan assets, target allocation, percentage 50.00%    
Maximum | Equity securities | Other Postretirement Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Defined benefit plan, plan assets, target allocation, percentage 20.00%    
Maximum | Fixed Income Securities | Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Defined benefit plan, plan assets, target allocation, percentage 60.00%    
Maximum | Fixed Income Securities | Other Postretirement Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Defined benefit plan, plan assets, target allocation, percentage 90.00%    
v3.25.0.1
Employee Benefit Plans - Health Care Rate Assumptions and Cost Trend Rate (Details) - Other Postretirement Benefits
Dec. 31, 2024
Dec. 31, 2023
Defined Benefit Plan Disclosure [Line Items]    
Health care cost trend rate - ultimate 4.50% 4.50%
Pre-65    
Defined Benefit Plan Disclosure [Line Items]    
Health care trend rate assumed for next year (pre-65/post-65) 8.50% 7.50%
Post-65    
Defined Benefit Plan Disclosure [Line Items]    
Health care trend rate assumed for next year (pre-65/post-65) 6.25% 6.50%
v3.25.0.1
Employee Benefit Plans - Estimated Future Benefit Payments and Subsidies (Details)
$ in Thousands
Dec. 31, 2024
USD ($)
Pension Benefits  
Defined Benefit Plan Disclosure [Line Items]  
2025 $ 22,280
2026 22,070
2027 21,870
2028 21,500
2029 21,170
2030-2034 98,020
Other Postretirement Benefits  
Defined Benefit Plan Disclosure [Line Items]  
2025 3,333
2026 3,235
2027 3,153
2028 3,064
2029 2,941
2030-2034 13,659
2025 48
2026 43
2027 37
2028 32
2029 27
2030-2034 $ 85
v3.25.0.1
Employee Benefit Plans - Pension Fair Value (Details) - Pension Benefits - USD ($)
$ in Thousands
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Defined Benefit Plan Disclosure [Line Items]      
Total assets measured at fair value $ 230,626 $ 248,558 $ 242,031
Cash equivalents      
Defined Benefit Plan Disclosure [Line Items]      
Investment within plan asset category, percentage 1.00% 7.00%  
U.S. Government securities      
Defined Benefit Plan Disclosure [Line Items]      
Investment within plan asset category, percentage 19.00% 7.00%  
Corporate bonds      
Defined Benefit Plan Disclosure [Line Items]      
Investment within plan asset category, percentage 39.00% 51.00%  
Other investments      
Defined Benefit Plan Disclosure [Line Items]      
Investment within plan asset category, percentage 17.00% 9.00%  
International companies      
Defined Benefit Plan Disclosure [Line Items]      
Investment within plan asset category, percentage 15.00% 15.00%  
US, large cap companies      
Defined Benefit Plan Disclosure [Line Items]      
Investment within plan asset category, percentage 9.00% 11.00%  
Fair Value, Inputs, Level 1, Level 2, and Level 3 | Cash equivalents      
Defined Benefit Plan Disclosure [Line Items]      
Total assets measured at fair value $ 4,512 $ 7,197  
Fair Value, Inputs, Level 1, Level 2, and Level 3 | U.S. companies      
Defined Benefit Plan Disclosure [Line Items]      
Total assets measured at fair value (2) (2)  
Fair Value, Inputs, Level 1, Level 2, and Level 3 | Collective and mutual funds      
Defined Benefit Plan Disclosure [Line Items]      
Total assets measured at fair value 166,383 172,980  
Fair Value, Inputs, Level 1, Level 2, and Level 3 | U.S. Government securities      
Defined Benefit Plan Disclosure [Line Items]      
Total assets measured at fair value 59,473 63,303  
Quoted Prices in Active Markets for Identical Assets  (Level 1)      
Defined Benefit Plan Disclosure [Line Items]      
Total assets measured at fair value 106,391 114,921  
Quoted Prices in Active Markets for Identical Assets  (Level 1) | Cash equivalents      
Defined Benefit Plan Disclosure [Line Items]      
Total assets measured at fair value 0 0  
Quoted Prices in Active Markets for Identical Assets  (Level 1) | U.S. companies      
Defined Benefit Plan Disclosure [Line Items]      
Total assets measured at fair value (2) (2)  
Quoted Prices in Active Markets for Identical Assets  (Level 1) | Collective and mutual funds      
Defined Benefit Plan Disclosure [Line Items]      
Total assets measured at fair value 72,777 84,761  
Quoted Prices in Active Markets for Identical Assets  (Level 1) | U.S. Government securities      
Defined Benefit Plan Disclosure [Line Items]      
Total assets measured at fair value 33,616 30,162  
Significant Other Observable Inputs  (Level 2)      
Defined Benefit Plan Disclosure [Line Items]      
Total assets measured at fair value 123,975 128,557  
Significant Other Observable Inputs  (Level 2) | Cash equivalents      
Defined Benefit Plan Disclosure [Line Items]      
Total assets measured at fair value 4,512 7,197  
Significant Other Observable Inputs  (Level 2) | U.S. companies      
Defined Benefit Plan Disclosure [Line Items]      
Total assets measured at fair value 0 0  
Significant Other Observable Inputs  (Level 2) | Collective and mutual funds      
Defined Benefit Plan Disclosure [Line Items]      
Total assets measured at fair value 93,606 88,219  
Significant Other Observable Inputs  (Level 2) | U.S. Government securities      
Defined Benefit Plan Disclosure [Line Items]      
Total assets measured at fair value 25,857 33,141  
Significant Unobservable Inputs  (Level 3)      
Defined Benefit Plan Disclosure [Line Items]      
Total assets measured at fair value 0 0  
Significant Unobservable Inputs  (Level 3) | Cash equivalents      
Defined Benefit Plan Disclosure [Line Items]      
Total assets measured at fair value 0 0  
Significant Unobservable Inputs  (Level 3) | U.S. companies      
Defined Benefit Plan Disclosure [Line Items]      
Total assets measured at fair value 0 0  
Significant Unobservable Inputs  (Level 3) | Collective and mutual funds      
Defined Benefit Plan Disclosure [Line Items]      
Total assets measured at fair value 0 0  
Significant Unobservable Inputs  (Level 3) | U.S. Government securities      
Defined Benefit Plan Disclosure [Line Items]      
Total assets measured at fair value 0 0  
Fair Value Measured at Net Asset Value Per Share      
Defined Benefit Plan Disclosure [Line Items]      
Total assets measured at fair value $ 260 $ 5,080  
v3.25.0.1
Employee Benefit Plans - Other Postretirement Fair value (Details) - Other Postretirement Benefits - USD ($)
$ in Thousands
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Defined Benefit Plan Disclosure [Line Items]      
Total assets measured at fair value $ 78,765 $ 79,234 $ 76,640
Corporate bonds      
Defined Benefit Plan Disclosure [Line Items]      
Postretirement investments in insurance contracts, percentage 41.00% 60.00%  
US, large cap companies      
Defined Benefit Plan Disclosure [Line Items]      
Postretirement investments in insurance contracts, percentage 19.00% 16.00%  
U.S. Government securities      
Defined Benefit Plan Disclosure [Line Items]      
Postretirement investments in insurance contracts, percentage 28.00% 15.00%  
US, small cap companies      
Defined Benefit Plan Disclosure [Line Items]      
Postretirement investments in insurance contracts, percentage 6.00% 5.00%  
Other investments      
Defined Benefit Plan Disclosure [Line Items]      
Postretirement investments in insurance contracts, percentage 6.00% 4.00%  
Fair Value, Inputs, Level 1, Level 2, and Level 3 | Cash equivalents      
Defined Benefit Plan Disclosure [Line Items]      
Total assets measured at fair value $ 4,373 $ 4,562  
Fair Value, Inputs, Level 1, Level 2, and Level 3 | U.S. companies      
Defined Benefit Plan Disclosure [Line Items]      
Total assets measured at fair value 2,880 2,369  
Fair Value, Inputs, Level 1, Level 2, and Level 3 | Insurance contract      
Defined Benefit Plan Disclosure [Line Items]      
Total assets measured at fair value 71,512 72,303  
Quoted Prices in Active Markets for Identical Assets  (Level 1)      
Defined Benefit Plan Disclosure [Line Items]      
Total assets measured at fair value 2,880 2,369  
Quoted Prices in Active Markets for Identical Assets  (Level 1) | Cash equivalents      
Defined Benefit Plan Disclosure [Line Items]      
Total assets measured at fair value 0 0  
Quoted Prices in Active Markets for Identical Assets  (Level 1) | U.S. companies      
Defined Benefit Plan Disclosure [Line Items]      
Total assets measured at fair value 2,880 2,369  
Quoted Prices in Active Markets for Identical Assets  (Level 1) | Insurance contract      
Defined Benefit Plan Disclosure [Line Items]      
Total assets measured at fair value 0 0  
Significant Other Observable Inputs  (Level 2)      
Defined Benefit Plan Disclosure [Line Items]      
Total assets measured at fair value 75,885 76,865  
Significant Other Observable Inputs  (Level 2) | Cash equivalents      
Defined Benefit Plan Disclosure [Line Items]      
Total assets measured at fair value 4,373 4,562  
Significant Other Observable Inputs  (Level 2) | U.S. companies      
Defined Benefit Plan Disclosure [Line Items]      
Total assets measured at fair value 0 0  
Significant Other Observable Inputs  (Level 2) | Insurance contract      
Defined Benefit Plan Disclosure [Line Items]      
Total assets measured at fair value 71,512 72,303  
Significant Unobservable Inputs  (Level 3)      
Defined Benefit Plan Disclosure [Line Items]      
Total assets measured at fair value 0 0  
Significant Unobservable Inputs  (Level 3) | Cash equivalents      
Defined Benefit Plan Disclosure [Line Items]      
Total assets measured at fair value 0 0  
Significant Unobservable Inputs  (Level 3) | U.S. companies      
Defined Benefit Plan Disclosure [Line Items]      
Total assets measured at fair value 0 0  
Significant Unobservable Inputs  (Level 3) | Insurance contract      
Defined Benefit Plan Disclosure [Line Items]      
Total assets measured at fair value $ 0 $ 0  
v3.25.0.1
Employee Benefit Plans - Nonqualified Benefit Plans Benefit Obligations (Details) - Supplemental Employee Retirement Plan - USD ($)
$ in Thousands
Dec. 31, 2024
Dec. 31, 2023
Defined Benefit Plan Disclosure [Line Items]    
Projected benefit obligation $ 52,007 $ 57,033
Accumulated benefit obligation $ 52,007 $ 57,033
v3.25.0.1
Employee Benefit Plans - Nonqualified Benefit Plans Components of NPBC (Details) - Supplemental Employee Retirement Plan - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Defined Benefit Plan Disclosure [Line Items]      
Interest cost $ 2,568 $ 2,740 $ 1,681
Recognized net actuarial loss 365 273 911
Net periodic benefit cost $ 2,933 $ 3,013 $ 2,592
v3.25.0.1
Employee Benefit Plans - Nonqualified Benefit Plans Weighted Average Assumptions (Details) - Supplemental Employee Retirement Plan
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Defined Benefit Plan Disclosure [Line Items]    
Benefit obligation discount rate 5.26% 4.73%
Net periodic benefit cost discount rate 4.73% 4.97%
v3.25.0.1
Employee Benefit Plans - Nonqualified Benefit Plans Future Benefit Payments (Details) - Supplemental Employee Retirement Plan
$ in Thousands
Dec. 31, 2024
USD ($)
Defined Benefit Plan Disclosure [Line Items]  
2025 $ 5,700
2026 5,610
2027 5,830
2028 5,560
2029 5,190
2030-2034 $ 20,920
v3.25.0.1
Employee Benefit Plans - Nonqualified Benefit Plans Investments (Details) - Supplemental Employee Retirement Plan - USD ($)
$ in Thousands
Dec. 31, 2024
Dec. 31, 2023
Defined Benefit Plan Disclosure [Line Items]    
Total investments $ 102,995 $ 100,648
Insurance contracts    
Defined Benefit Plan Disclosure [Line Items]    
Total investments 59,282 62,936
Life insurance    
Defined Benefit Plan Disclosure [Line Items]    
Total investments 30,834 31,303
Other    
Defined Benefit Plan Disclosure [Line Items]    
Total investments $ 12,879 $ 6,409
v3.25.0.1
Employee Benefit Plans - Multiemployer Plans Participation by Plan (Details) - Pension Benefits - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Multiemployer Plans [Line Items]      
Total contributions $ 1,434 $ 1,690 $ 1,613
Idaho Plumbers and Pipefitters Pension Plan      
Multiemployer Plans [Line Items]      
Employer identification number 826010346    
Pension plan number 001    
Pension Protection Act Zone Status Green Green  
Pension Protection Act Zone Status, Date May 31, 2024 May 31, 2023  
FIP/RP Status Pending/Implemented No    
Contributions $ 1,434 $ 1,690 $ 1,613
Surcharge Imposed No    
Expiration Date of Collective Bargaining Agreement Mar. 31, 2027    
v3.25.0.1
Regulatory Matters - MTPSC (Details) - Montana-Dakota Utilities Co. - Natural gas distribution - MTPSC - USD ($)
$ in Millions
Jan. 14, 2025
Oct. 15, 2024
Jul. 15, 2024
Public Utilities, General Disclosures [Line Items]      
Public utilities, requested rate increase (decrease), amount   $ 8.0 $ 9.4
Public utilities, requested rate increase (decrease), percentage   10.20% 11.10%
Subsequent Event      
Public Utilities, General Disclosures [Line Items]      
Public utilities, interim rate increase (decrease), amount $ 7.7    
v3.25.0.1
Regulatory Matters - NDPSC (Details) - NDPSC - Montana-Dakota Utilities Co. - USD ($)
$ in Millions
Nov. 01, 2024
Dec. 13, 2023
Nov. 01, 2023
Sep. 16, 2024
Public Utilities, General Disclosures [Line Items]        
Public utilities, annual revenue increase (decrease)       $ 9.4
Public utilities, annual revenue increase (decrease), percentage       6.10%
Natural gas distribution        
Public Utilities, General Disclosures [Line Items]        
Public utilities, requested rate increase (decrease), amount     $ 11.6  
Public utilities, requested rate increase (decrease), percentage     7.50%  
Public utilities, interim rate increase (decrease), amount   $ 10.1    
Public utilities, interim rate increase (decrease), percentage   6.50%    
Electric        
Public Utilities, General Disclosures [Line Items]        
Requested renewable resource cost adjustment rate tariff $ 18.3      
Public utilities, approved rate increase (decrease), amount $ 2.8      
v3.25.0.1
Regulatory Matters - WUTC (Details) - Natural gas distribution - WUTC - Cascade Natural Gas - USD ($)
$ in Millions
Dec. 11, 2024
Mar. 29, 2024
Pending Rate Case, Multi-Year, Year One    
Public Utilities, General Disclosures [Line Items]    
Public utilities, requested rate increase (decrease), amount $ 29.8 $ 43.8
Public utilities, requested rate increase (decrease), percentage 7.90% 11.60%
Pending Rate Case, Multi-Year, Year Two    
Public Utilities, General Disclosures [Line Items]    
Public utilities, requested rate increase (decrease), amount $ 10.8 $ 11.7
Public utilities, requested rate increase (decrease), percentage 2.60% 2.80%
v3.25.0.1
Regulatory matters - WYPSC (Details) - Natural gas distribution - WYPSC - Montana-Dakota Utilities Co. - Pending Rate Case
$ in Millions
Oct. 31, 2024
USD ($)
Public Utilities, General Disclosures [Line Items]  
Public utilities, requested rate increase (decrease), amount $ 2.6
Public utilities, requested rate increase (decrease), percentage 14.00%
v3.25.0.1
Regulatory Matters - FERC (Details)
$ in Millions
Aug. 29, 2024
USD ($)
FERC | Montana-Dakota Utilities Co. | Transmission Formula  
Public Utilities, General Disclosures [Line Items]  
Public utilities, requested rate increase (decrease), amount $ 19.7
v3.25.0.1
Commitments and Contingencies - Litigation (Details) - USD ($)
$ in Thousands
Dec. 31, 2024
Dec. 31, 2023
Commitments and Contingencies Disclosure [Abstract]    
Potential liabilities related to litigation and environmental matters $ 24,100 $ 22,500
Loss contingency, receivable 24 152
Loss contingency, regulatory asset $ 22,900 $ 21,600
v3.25.0.1
Commitments and Contingencies - Environmental matters (Details)
$ in Thousands
 12 Months Ended
Dec. 31, 2024
USD ($)
Missoula, MT manufactured gas plant site  
Site Contingency [Line Items]  
Total estimated costs for site remediation $ 560
Environmental matters estimated investigative costs 2,000
Environmental matters accrual for site remediation 645
Incurred costs for site remedial investigation 1,200
Bremerton, WA manufactured gas plant site  
Site Contingency [Line Items]  
Environmental matters accrual for site remediation 17,500
Total estimated costs for site remedial investigation and feasibility study 16,000
Incurred costs for site remedial investigation and feasibility study 11,700
Environmental matters accrual of investigative costs 4,300
Bellingham, WA manufactured gas plant site  
Site Contingency [Line Items]  
Site contingency, loss exposure not accrued, preferred alternative estimate 9,300
Minimum | Bremerton, WA manufactured gas plant site  
Site Contingency [Line Items]  
Site contingency, loss exposure not accrued, best estimate 13,600
Minimum | Bellingham, WA manufactured gas plant site  
Site Contingency [Line Items]  
Site contingency, loss exposure not accrued, best estimate 8,000
Maximum | Bremerton, WA manufactured gas plant site  
Site Contingency [Line Items]  
Site contingency, loss exposure not accrued, best estimate 71,500
Maximum | Bellingham, WA manufactured gas plant site  
Site Contingency [Line Items]  
Site contingency, loss exposure not accrued, best estimate $ 20,400
v3.25.0.1
Commitments and Contingencies - Purchase Commitments (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Long-term Purchase Commitment [Line Items]      
Commitment term 35 years    
Amounts purchased under various commitments $ 841,700 $ 1,000,000 $ 870,600
Inventories      
Purchase commitments due      
2025 658,012    
2026 310,894    
2027 210,152    
2028 177,613    
2029 147,081    
Thereafter $ 1,221,125    
v3.25.0.1
Commitments and Contingencies - Guarantees (Details)
Dec. 31, 2024
USD ($)
Guarantor Obligations [Line Items]  
Letters of credit set to expire in next fiscal year $ 14,300,000
Outstanding letters of credit 0
Amount of surety bonds outstanding 15,600,000
Line of Credit  
Guarantor Obligations [Line Items]  
Line of credit facility, maximum borrowing capacity $ 14,300,000
v3.25.0.1
Commitments and Contingencies - Leases (Details)
Dec. 31, 2024
Loss Contingencies [Line Items]  
Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration] Other accrued liabilities
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration] Other
Vehicles and Equipment  
Loss Contingencies [Line Items]  
Remaining lease term 5 years
Buildings and Easements  
Loss Contingencies [Line Items]  
Remaining lease term 35 years
v3.25.0.1
Commitments and Contingencies - Schedule of Lease Costs (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Leases [Abstract]      
Short-term lease cost $ 1,549 $ 1,646 $ 1,373
Operating lease cost 3,069 2,871 2,497
Variable lease cost 819 676 413
Total lease costs $ 5,437 $ 5,193 $ 4,283
Weighted average remaining lease term 12 years 7 months 24 days 15 years 4 months 6 days 15 years 1 month 24 days
Weighted average discount rate 6.08% 4.88% 4.65%
Cash paid for amounts included in the measurement of lease liabilities $ 3,063 $ 2,868 $ 2,500
v3.25.0.1
Commitments and Contingencies - Schedule of Operating Lease Liabilities Undiscounted Cash Flows Maturity (Details)
$ in Thousands
Dec. 31, 2024
USD ($)
Leases [Abstract]  
2025 $ 3,034
2026 2,648
2027 2,011
2028 1,570
2029 1,492
Thereafter 20,808
Total 31,563
Less discount 10,654
Total operating lease liabilities $ 20,909
v3.25.0.1
Commitments and Contingencies - Variable Interest Entities (Details)
$ in Millions
Dec. 31, 2024
USD ($)
Fuel Contract  
Variable Interest Entities [Line Items]  
Variable interest entity, reporting entity involvement, maximum loss exposure, amount $ 25.6
v3.25.0.1
Subsequent Events (Details) - Jointly Owned Electricity Generation Plant - Badger Wind LLC - Subsequent Event
$ in Millions
Feb. 13, 2025
USD ($)
MW
Subsequent Event [Line Items]  
Proportionate ownership share 49.00%
Net generating capacity 250
Payments to purchase ownership | $ $ 294.0
Wind generation ownership 122.5
v3.25.0.1
Schedule I - Condensed Financial Information of Registrant - Condensed Statements of Income and Comprehensive Income (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Condensed Financial Statements, Captions [Line Items]      
Revenues from contracts with customers $ 1,752,995 $ 1,805,807 $ 1,754,158
Operating expenses 1,492,336 1,578,408 1,546,428
Operating income 265,642 224,944 200,870
Realized gain on tax-free exchange of the retained shares in Knife River 0 186,556 0
Interest expense 108,347 104,624 80,683
Income before income taxes 198,662 340,330 123,447
Income taxes 17,589 10,213 6,195
Income from continuing operations 181,073 330,117 117,252
Discontinued operations, net of tax 100,035 84,590 250,237
Net income 281,108 414,707 367,489
Comprehensive income attributable to common stockholders 282,694 414,600 377,910
MDU Resources Group, Inc.      
Condensed Financial Statements, Captions [Line Items]      
Revenues from contracts with customers 0 0 0
Operating expenses 4,416 9,668 1,636
Operating income (4,416) (9,668) (1,636)
Realized gain on tax-free exchange of the retained shares in Knife River 0 186,556 0
Interest expense 642 7,109 0
Income before income taxes (5,058) 169,779 (1,636)
Income taxes (2,324) (4,220) (400)
Equity in earnings of subsidiaries from continuing operations 183,807 156,118 118,488
Income from continuing operations 181,073 330,117 117,252
Equity in earnings of subsidiaries from discontinued operations 140,042 143,181 261,701
Discontinued operations, net of tax (40,007) (58,591) (11,464)
Net income 281,108 414,707 367,489
Comprehensive income attributable to common stockholders $ 282,694 $ 414,600 $ 377,910
v3.25.0.1
Schedule I - Condensed Financial Information of Registrant - Condensed Balance Sheets (Details) - USD ($)
$ in Thousands
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Current assets:        
Cash and cash equivalents $ 66,904 $ 60,473    
Receivables, net 274,303 250,153    
Prepayments and other current assets 64,676 66,431    
Total current assets 666,259 1,363,723    
Noncurrent assets        
Investments 115,459 112,475    
Other 244,722 211,369    
Total noncurrent assets 6,372,559 6,469,436    
Total assets 7,038,818 7,833,159 $ 9,660,781  
Current liabilities:        
Accounts payable 150,070 159,975    
Taxes payable 43,372 49,553    
Dividends payable 26,511 25,461    
Accrued compensation 35,264 40,792    
Other accrued liabilities 124,514 129,592    
Total current liabilities 678,598 1,075,733    
Noncurrent liabilities:        
Long-term debt, net of debt issuance costs 2,130,910 2,104,904    
Other 231,895 209,882    
Total noncurrent liabilities 3,669,646 3,852,193    
Commitments and contingencies    
Stockholders' equity:        
Common stock Authorized - 500,000,000 shares, $1.00 par value Shares issued - 203,934,578 at December 31, 2024 and 203,689,090 at December 31, 2023 203,935 203,689    
Other paid-in capital 1,473,738 1,466,235    
Retained earnings 1,029,699 1,253,693    
Accumulated other comprehensive loss (16,798) (18,384)    
Total stockholders' equity 2,690,574 2,905,233 3,587,129 $ 3,382,874
Total liabilities and stockholders' equity 7,038,818 7,833,159    
MDU Resources Group, Inc.        
Current assets:        
Cash and cash equivalents 29,361 33,039 $ 19,486 $ 6,159
Receivables, net 2,777 6,568    
Taxes receivable 5,799 0    
Prepayments and other current assets 3,210 8,261    
Total current assets 73,102 78,394    
Noncurrent assets        
Investments 37,264 37,722    
Deferred income taxes 13,569 12,596    
Operating lease right-of-use assets 160 31    
Other 2,874 2,593    
Total noncurrent assets 2,915,178 3,257,064    
Total assets 2,988,280 3,335,458    
Current liabilities:        
Accounts payable 4,076 4,264    
Taxes payable 0 542    
Dividends payable 26,511 25,461    
Accrued compensation 7,939 9,651    
Operating lease liabilities due within one year 60 25    
Other accrued liabilities 7,653 8,008    
Total current liabilities 245,351 185,493    
Noncurrent liabilities:        
Long-term debt, net of debt issuance costs (536) 57,048    
Operating lease liabilities 100 6    
Other 52,791 187,678    
Total noncurrent liabilities 52,355 244,732    
Commitments and contingencies    
Stockholders' equity:        
Common stock Authorized - 500,000,000 shares, $1.00 par value Shares issued - 203,934,578 at December 31, 2024 and 203,689,090 at December 31, 2023 203,935 203,689    
Other paid-in capital 1,473,738 1,466,235    
Retained earnings 1,029,699 1,253,693    
Accumulated other comprehensive loss (16,798) (18,384)    
Total stockholders' equity 2,690,574 2,905,233    
Total liabilities and stockholders' equity 2,988,280 3,335,458    
MDU Resources Group, Inc. | Subsidiaries        
Current assets:        
Receivables, net 31,955 30,526    
Noncurrent assets        
Investments 2,861,311 3,146,122    
Notes receivable from subsidiaries 0 58,000    
Current liabilities:        
Accounts payable 1,077 3,435    
Notes payable to subsidiaries $ 198,035 $ 134,107    
v3.25.0.1
Schedule I - Condensed Financial Information of Registrant - Condensed Balance Sheets - Parenthetical (Details) - $ / shares
Dec. 31, 2024
Dec. 31, 2023
Condensed Financial Statements, Captions [Line Items]    
Common stock, authorized (in shares) 500,000,000 500,000,000
Common stock, par value per share (in usd per share) $ 1.00 $ 1.00
Common stock, issued (in shares) 203,934,578 203,689,090
MDU Resources Group, Inc.    
Condensed Financial Statements, Captions [Line Items]    
Common stock, authorized (in shares) 500,000,000 500,000,000
Common stock, par value per share (in usd per share) $ 1.00 $ 1.00
Common stock, issued (in shares) 203,934,578 203,689,090
v3.25.0.1
Schedule I - Condensed Financial Information of Registrant - Condensed Statements of Cash Flows (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Operating activities:      
Net cash provided by continuing operations $ 411,813 $ 305,333 $ 321,615
Net cash provided by discontinued operations 90,505 27,294 188,449
Net cash provided by operating activities 502,318 332,627 510,064
Investing activities:      
Investments (5,155) (2,423) (2,571)
Net cash used in continuing operations (523,827) (465,129) (456,929)
Financing activities:      
Issuance of short-term borrowings 0 810,000 11,500
Repayment of short-term borrowings (95,000) (433,901) 0
Issuance of long-term debt 308,600 594,700 214,969
Repayment of long-term debt (182,135) (568,883) (38,764)
Debt issuance costs (2,456) (2,521) (1,129)
Costs of issuance of common stock (50) 0 (150)
Dividends paid (102,939) (161,316) (176,915)
Repurchase of common stock 0 (4,811) (7,399)
Tax withholding on stock-based compensation (2,623) (3,040) (4,904)
Net cash (used in) provided by continuing operations (76,603) 230,228 (2,792)
Net cash provided by (used in) discontinued operations 116,899 (25,606) 157,965
Net cash provided by financing activities 40,296 204,622 155,173
(Decrease) increase in cash, cash equivalents and restricted cash (10,071) (3,542) 26,356
Cash, cash equivalents and restricted cash - beginning of year 60,473    
Cash, cash equivalents and restricted cash - end of year 66,904 60,473  
MDU Resources Group, Inc.      
Operating activities:      
Net cash provided by continuing operations 482,195 282,132 253,663
Net cash provided by discontinued operations (40,007) (58,591) (11,464)
Net cash provided by operating activities 442,188 223,541 242,199
Investing activities:      
Investments 2,253 7,422 (885)
Repayment (issuance) of notes receivable 58,000 (58,000) 0
Net cash used in continuing operations (150,747) (526,578) (45,885)
Financing activities:      
Issuance of short-term borrowings 0 535,000 0
Repayment of short-term borrowings 0 (242,401) 0
Issuance of long-term debt 0 443,000 0
Repayment of long-term debt (58,000) (385,000) 0
Debt issuance costs (401) (952) 0
Costs of issuance of common stock (50) 0 (149)
Dividends paid (102,939) (161,316) (176,915)
Repurchase of common stock 0 (2,270) (3,525)
Tax withholding on stock-based compensation (1,729) (1,471) (2,398)
Net cash (used in) provided by continuing operations (163,119) 184,590 (182,987)
Net cash provided by (used in) discontinued operations (132,000) 132,000 0
Net cash provided by financing activities (295,119) 316,590 (182,987)
(Decrease) increase in cash, cash equivalents and restricted cash (3,678) 13,553 13,327
Cash, cash equivalents and restricted cash - beginning of year 33,039 19,486 6,159
Cash, cash equivalents and restricted cash - end of year 29,361 33,039 19,486
MDU Resources Group, Inc. | Subsidiaries      
Investing activities:      
Investments $ (211,000) $ (476,000) $ (45,000)
v3.25.0.1
Schedule I - Condensed Financial Information of Registrant - Notes to Condensed Financial Statements (Details)
 12 Months Ended
Nov. 01, 2024
USD ($)
Nov. 15, 2023
USD ($)
Dec. 31, 2024
USD ($)
Dec. 31, 2023
USD ($)
Dec. 31, 2022
USD ($)
May 31, 2023
USD ($)
Condensed Financial Statements, Captions [Line Items]            
Short-term borrowings     $ 0 $ 95,000,000    
Long-term debt     2,292,610,000 2,166,223,000    
Repayments of long-term debt     182,135,000 568,883,000 $ 38,764,000  
Repayment of short-term borrowings     95,000,000 433,901,000 0  
Long-term debt, maturities year two     $ 144,700,000      
MDU Resources Group, Inc. | Term Loan Agreement            
Condensed Financial Statements, Captions [Line Items]            
Long-term debt           $ 375,000,000
Repayments of long-term debt $ 190,000,000 $ 185,000,000        
MDU Resources Group, Inc. | Revolving Credit Facility            
Condensed Financial Statements, Captions [Line Items]            
Ratio of total debt to total capitalization     0.65      
Long-term debt           200,000,000
MDU Resources Group, Inc. | Revolving Credit Facility            
Condensed Financial Statements, Captions [Line Items]            
Short-term borrowings       0   $ 150,000,000
MDU Resources Group, Inc.            
Condensed Financial Statements, Captions [Line Items]            
Repayments of long-term debt     $ 58,000,000 385,000,000 0  
Repayment of short-term borrowings     0 242,401,000 0  
Long-term debt, maturities year two     0      
Cash dividends paid to parent company by consolidated subsidiaries     $ 418,300,000 $ 165,500,000 $ 242,100,000  
v3.25.0.1
Jointly Owned Facilities (Details) - USD ($)
$ in Thousands
Dec. 31, 2024
Dec. 31, 2023
Jointly Owned Electricity Generation Plant | Big Stone Station    
Jointly Owned Utility Plant Interests [Line Items]    
Proportionate ownership share 22.70%  
Utility plant in service $ 155,302 $ 159,437
CWIP 318 197
Less accumulated depreciation 55,327 52,264
Utility plant in services net $ 100,293 107,370
Jointly Owned Electricity Generation Plant | Coyote Station    
Jointly Owned Utility Plant Interests [Line Items]    
Proportionate ownership share 25.00%  
Utility plant in service $ 160,343 160,208
CWIP 755 159
Less accumulated depreciation 115,133 113,187
Utility plant in services net $ 45,965 47,180
Jointly Owned Electricity Generation Plant | Wygen III    
Jointly Owned Utility Plant Interests [Line Items]    
Proportionate ownership share 25.00%  
Utility plant in service $ 67,851 66,852
CWIP 97 127
Less accumulated depreciation 15,340 13,728
Utility plant in services net $ 52,608 53,251
Jointly Owned Electricity Transmission and Distribution System | BSSE    
Jointly Owned Utility Plant Interests [Line Items]    
Proportionate ownership share 50.00%  
Utility plant in service $ 111,043 107,260
CWIP 0 0
Less accumulated depreciation 10,359 8,111
Utility plant in services net $ 100,684 99,149
Jointly Owned Electricity Transmission and Distribution System | JETx    
Jointly Owned Utility Plant Interests [Line Items]    
Proportionate ownership share 50.00%  
Utility plant in service $ 0 0
CWIP 6,112 1,372
Less accumulated depreciation 0 0
Utility plant in services net $ 6,112 $ 1,372