MDU RESOURCES GROUP INC, 10-Q filed on 5/7/2026
Quarterly Report
v3.26.1
Cover Page - shares
 3 Months Ended
Mar. 31, 2026
Apr. 30, 2026
Cover [Abstract]    
Document Type 10-Q  
Document Quarterly Report true  
Document Period End Date Mar. 31, 2026  
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 $1.00 per share  
Trading Symbol MDU  
Security Exchange Name NYSE  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Filer Category Large Accelerated Filer  
Entity Small Business false  
Entity Emerging Growth Company false  
Entity Shell Company false  
Entity Common Stock, Shares Outstanding   209,006,024
Entity Central Index Key 0000067716  
Current Fiscal Year End Date --12-31  
Document Fiscal Year Focus 2026  
Document Fiscal Period Focus Q1  
Amendment Flag false  
v3.26.1
Consolidated Statements of Income - USD ($)
shares in Thousands, $ in Thousands
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Income Statement [Abstract]    
Operating revenues  $ 605,977 $ 674,833
Operating expenses:    
Purchased natural gas sold 239,391 317,157
Electric fuel and purchased power 46,067 43,748
Operation and maintenance 114,905 111,047
Depreciation and amortization 54,179 51,261
Taxes, other than income 35,730 38,757
Total operating expenses 490,272 561,970
Operating income 115,705 112,863
Other income 2,605 4,997
Interest expense 32,685 26,822
Income before income taxes 85,625 91,038
Income taxes 4,678 8,571
Income from continuing operations 80,947 82,467
Discontinued operations, net of tax (130) (502)
Net income $ 80,817 $ 81,965
Earnings per share - basic:    
Income from continuing operations (in usd per share) $ 0.39 $ 0.40
Discontinued operations, net of tax (in usd per share) 0 0
Earnings per share - basic (in usd per share) 0.39 0.40
Earnings per share - diluted:    
Income from continuing operations (in usd per share) 0.39 0.40
Discontinued operations, net of tax (in usd per share) 0 0
Earnings per share - diluted (in usd per share) $ 0.39 $ 0.40
Weighted average common shares outstanding - basic (in shares) 205,438 204,142
Weighted average common shares outstanding - diluted (in shares) 206,994 204,959
v3.26.1
Consolidated Statements of Comprehensive Income - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Statement of Comprehensive Income [Abstract]    
Net income $ 80,817 $ 81,965
Postretirement liability adjustment:    
Amortization of postretirement liability losses included in net periodic benefit credit, net of tax of $34 and $18 for the three months ended in 2026 and 2025, respectively 175 118
Net unrealized (loss) gain on available-for-sale investments:    
Net unrealized (loss) gain on available-for-sale investments arising during the period, net of tax of $(10) and $19 for the three months ended in 2026 and 2025, respectively (38) 71
Reclassification adjustment for loss on available-for-sale investments included in net income, net of tax of $1 and $1 for the three months ended in 2026 and 2025, respectively 3 3
Net unrealized (loss) gain on available-for-sale investments (35) 74
Other comprehensive income 140 192
Comprehensive income attributable to common stockholders $ 80,957 $ 82,157
v3.26.1
Consolidated Statements of Comprehensive Income (Parenthetical) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Statement of Comprehensive Income [Abstract]    
Amortization of postretirement liability losses included in net periodic benefit credit, tax $ 34 $ 18
Net unrealized (loss) gain on available-for-sale investments arising during the period, tax (10) 19
Reclassification adjustment for loss on available-for-sale investments included in net income, tax $ 1 $ 1
v3.26.1
Consolidated Balance Sheets - USD ($)
$ in Thousands
Mar. 31, 2026
Dec. 31, 2025
Mar. 31, 2025
Current assets:      
Cash, cash equivalents and restricted cash $ 53,295 $ 28,212 $ 59,541
Receivables, net 222,967 258,631 269,246
Current regulatory assets 190,679 179,579 143,341
Inventories 19,485 39,052 18,457
Current environmental allowances 25,238 26,194 23,039
Prepayments and other current assets 47,886 40,768 27,927
Total current assets 559,550 572,436 541,551
Noncurrent assets:      
Property, plant and equipment 8,325,077 8,264,972 7,617,007
Less accumulated depreciation and amortization 2,327,742 2,304,787 2,238,371
Net property, plant and equipment 5,997,335 5,960,185 5,378,636
Goodwill 345,736 345,736 345,736
Regulatory assets 293,973 297,218 312,008
Investments 117,920 121,177 117,599
Environmental allowances 148,896 112,376 86,130
Other 220,526 213,078 179,814
Total noncurrent assets  7,124,386 7,049,770 6,419,923
Total assets 7,683,936 7,622,206 6,961,474
Current liabilities:      
Long-term debt due within one year 214,700 144,700 161,700
Accounts payable 124,377 148,970 109,133
Regulatory liabilities due within one year 148,409 148,584 140,165
Taxes payable 44,217 44,686 65,218
Dividends payable 28,659 28,614 26,563
Accrued compensation 20,097 34,666 18,175
Current environmental obligations 24,086 24,086 19,561
Other accrued liabilities 113,797 110,917 94,061
Total current liabilities  718,342 685,223 634,576
Noncurrent liabilities:      
Long-term debt 2,381,296 2,532,155 2,031,976
Deferred income taxes 448,260 437,286 429,825
Regulatory liabilities 474,957 472,329 463,879
Asset retirement obligations 436,209 431,587 410,715
Environmental obligations 135,857 108,448 75,077
Other 185,377 182,261 172,290
Total noncurrent liabilities  4,061,956 4,164,066 3,583,762
Commitments and contingencies
Stockholders' equity:      
Common stock Authorized - 500,000,000 shares, $1.00 par value Shares issued - 209,006,024 at March 31, 2026, 204,331,170 at March 31, 2025 and 204,382,821 at December 31, 2025 209,006 204,383 204,331
Other paid-in capital 1,550,364 1,476,355 1,470,512
Retained earnings 1,160,843 1,108,894 1,084,899
Accumulated other comprehensive loss (16,575) (16,715) (16,606)
Total stockholders' equity 2,903,638 2,772,917 2,743,136
Total liabilities and stockholders' equity  $ 7,683,936 $ 7,622,206 $ 6,961,474
v3.26.1
Consolidated Balance Sheets (Parenthetical) - $ / shares
Mar. 31, 2026
Dec. 31, 2025
Mar. 31, 2025
Statement of Financial Position [Abstract]      
Common stock, authorized (in shares) 500,000,000 500,000,000 500,000,000
Common stock, par value per share (in usd per share) $ 1.00 $ 1.00 $ 1.00
Common stock, issued (in shares) 209,006,024 204,382,821 204,331,170
v3.26.1
Consolidated Statements of Equity - USD ($)
$ in Thousands
Total
Common Stock
Other Paid-in Capital
Retained Earnings
Accumulated Other Comprehensive Loss
Common stock, beginning balance (in shares) at Dec. 31, 2024   203,934,578      
Beginning balance at Dec. 31, 2024 $ 2,690,574 $ 203,935 $ 1,473,738 $ 1,029,699 $ (16,798)
Increase (Decrease) in Stockholders' Equity [Roll Forward]          
Net income 81,965     81,965  
Other comprehensive income 192       192
Dividends declared on common stock (26,765)     (26,765)  
Stock-based compensation 1,646   1,646    
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings (in shares)   396,592      
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings $ (4,476) $ 396 (4,872)    
Common stock, ending balance (in shares) at Mar. 31, 2025 204,331,170 204,331,170      
Ending balance at Mar. 31, 2025 $ 2,743,136 $ 204,331 1,470,512 1,084,899 (16,606)
Common stock, beginning balance (in shares) at Dec. 31, 2025 204,382,821 204,382,821      
Beginning balance at Dec. 31, 2025 $ 2,772,917 $ 204,383 1,476,355 1,108,894 (16,715)
Increase (Decrease) in Stockholders' Equity [Roll Forward]          
Net income 80,817     80,817  
Other comprehensive income 140       140
Dividends declared on common stock (28,868)     (28,868)  
Stock-based compensation 1,932   1,932    
Issuance of common stock, net (in shares)   4,300,000      
Issuance of common stock, net 81,159 $ 4,300 76,859    
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings (in shares)   323,203      
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings $ (4,459) $ 323 (4,782)    
Common stock, ending balance (in shares) at Mar. 31, 2026 209,006,024 209,006,024      
Ending balance at Mar. 31, 2026 $ 2,903,638 $ 209,006 $ 1,550,364 $ 1,160,843 $ (16,575)
v3.26.1
Consolidated Statements of Cash Flows - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Operating activities:    
Net income $ 80,817 $ 81,965
Loss from discontinued operations, net of tax (130) (502)
Income from continuing operations 80,947 82,467
Adjustments to reconcile net income to net cash provided by operating activities:    
Depreciation and amortization 54,179 51,261
Deferred income taxes 8,191 (13,687)
Provision for credit losses 2,622 3,152
Amortization of debt issuance costs 366 309
Employee stock-based compensation costs 1,932 1,646
Pension and postretirement benefit plan net periodic benefit cost (credit) 348 (267)
Unrealized losses on other mark-to-market investments 505 470
Changes in current assets and liabilities, net of acquisitions:    
Receivables 33,042 15,128
Inventories 19,303 26,590
Other current assets (14,344) 92,739
Accounts payable (14,751) (28,034)
Other current liabilities (11,182) (11,324)
Pension and postretirement benefit plan contributions (220) (385)
Other noncurrent changes (11,600) (2,091)
Net cash provided by continuing operations 149,338 217,974
Net cash used in discontinued operations (130) (502)
Net cash provided by operating activities 149,208 217,472
Investing activities:    
Capital expenditures (92,412) (93,034)
(Cost of removal, net)/Salvage value, net (738) 869
Purchase of investment securities (2,048) (2,574)
Proceeds from investment securities 4,000 0
Net cash used in investing activities (91,198) (94,739)
Financing activities:    
Issuance of long-term debt 138,449 0
Repayment of long-term debt (218,937) (99,104)
Debt issuance costs (525) (5)
Issuance of common stock, net 81,159 0
Dividends paid (28,614) (26,511)
Tax withholding on stock-based compensation (4,459) (4,476)
Net cash used in financing activities (32,927) (130,096)
Increase (decrease) in cash, cash equivalents and restricted cash 25,083 (7,363)
Cash, cash equivalents and restricted cash - beginning of year 28,212 66,904
Cash, cash equivalents and restricted cash - end of period 53,295 59,541
Supplemental cash flow information:    
Interest, net [1] 23,508 19,929
Income taxes (refunded) paid, net (1,676) 172
Property, plant and equipment additions in accounts payable 35,496 23,917
Right-of-use assets obtained in exchange for new operating lease liabilities $ 68 $ 129
[1]
*AFUDC - borrowed was $2.0 million and $1.8 million for the three months ended March 31, 2026 and 2025, respectively.
v3.26.1
Consolidated Statements of Cash Flows (Parenthetical) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Statement of Cash Flows [Abstract]    
AFUDC borrowed $ 2.0 $ 1.8
v3.26.1
Basis of presentation
 3 Months Ended
Mar. 31, 2026
Accounting Policies [Abstract]  
Basis of presentation Basis of presentation
The accompanying consolidated interim financial statements were prepared in accordance with GAAP for interim financial information and with the instructions to Form 10-Q and Rule 10-01 of Regulation S-X. Interim financial statements do not include all disclosures provided in annual financial statements and, accordingly, these financial statements should be read in conjunction with those appearing in the 2025 Annual Report. The information is unaudited but includes all adjustments that are, in the opinion of management, necessary for a fair presentation of the accompanying consolidated interim financial statements and are of a normal recurring nature. Depreciation and amortization expense is reported separately on the Consolidated Statements of Income and therefore is excluded from the other line items within operating expenses.
Discontinued operations includes certain costs associated with legacy business activities other than certain general and administrative costs (reflected in operation and maintenance expense) and interest expense, which were previously allocated to the Company's former businesses which do not meet the criteria for discontinued operations. Discontinued operations are not material to the financial statements for any period presented. Unless otherwise indicated, the amounts presented in the accompanying condensed notes to the consolidated financial statements relate to the Company's continuing operations. For more information on discontinued operations, see Note 3.
Management has also evaluated the impact of events occurring after March 31, 2026, up to the date of issuance of these consolidated interim financial statements on May 7, 2026, that would require recognition or disclosure in the Consolidated Financial Statements.
v3.26.1
New accounting standards
 3 Months Ended
Mar. 31, 2026
Accounting Standards Update and Change in Accounting Principle [Abstract]  
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 issued accounting standards not yet adopted
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.
ASU 2025-05
Measurement of
Credit Losses for
Accounts Receivable
and Contract Assets
In July 2025, the FASB issued guidance on applying a practical expedient when estimating expected credit losses on current accounts receivable and/or current contract assets arising from transactions under ASC Topic 606 - Revenue from Contracts with Customers.
Effective for annual
reporting periods
beginning after December
15, 2025.
The Company is currently
evaluating the impact the guidance will have on its results of operations, financial position, cash flows, and disclosures for the year ended December 31, 2026.
ASU 2025-06
Targeted
Improvements to the Accounting of Internal-Use
Software
In September 2025, the FASB issued guidance on accounting for
capitalization of development costs for internal-use software under
ASC Subtopic 350-40 and the transition approaches to use.
Effective for annual reporting periods beginning after December
15, 2027.
The Company is currently
evaluating the impact the guidance will have on its results of operations, financial position, cash flows, and disclosures for the year ended December 31, 2028.
ASU 2025-10
Accounting for
Government Grants Received By Business Entities
In December 2025, the FASB issued guidance on accounting for government grants received by business entities that are related to an asset (purchase, construction, or acquisition of a long-lived asset or inventory) or income (reimbursements to a business entity for operating expenses).
Effective for annual reporting periods beginning after December
15, 2028.
The Company is currently
evaluating the impact the guidance will have on its results of operations, financial position, cash flows, and disclosures for the year ended December 31, 2029.
v3.26.1
Discontinued operations
 3 Months Ended
Mar. 31, 2026
Discontinued Operations and Disposal Groups [Abstract]  
Discontinued operations Discontinued operations
Discontinued operations includes certain costs associated with legacy business activities other than certain general and administrative costs (reflected in operation and maintenance expense) and interest expense, which were previously allocated to the company's former businesses which do not meet the criteria for discontinued operations.
On October 31, 2024, the Company completed the separation of Everus, its former construction services segment, into a new independent, publicly-traded company. As a result of the separation, the Company provided to Everus and Everus provided to the Company transition services in accordance with the TSA entered into on October 31, 2024. For the three months ended March 31, 2026, the Company received $1.2 million for these related activities. For the three months ended March 31, 2025, the Company received $1.8 million and paid $13,000 for these related activities. All transition services were completed as of March 31, 2026.
Separation related costs of $130,000 and $502,000, net of tax, were incurred during the three months ended March 31, 2026 and 2025, respectively. 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 Everus on its balance sheet as of March 31, 2026, March 31, 2025, or December 31, 2025.
v3.26.1
Seasonality of operations
 3 Months Ended
Mar. 31, 2026
Organization, Consolidation and Presentation of Financial Statements [Abstract]  
Seasonality of operations Seasonality of operations
Some of the Company's operations are highly seasonal and revenues from, and certain expenses for, such operations may fluctuate significantly among quarterly periods. Accordingly, the interim results for particular businesses, and for the Company as a whole, may not be indicative of results for the full fiscal year.
v3.26.1
Receivables and allowance for expected credit losses
 3 Months Ended
Mar. 31, 2026
Credit Loss [Abstract]  
Receivables and allowance for expected credit loss 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.
Details of the Company's expected credit losses were as follows:
ElectricNatural gas
distribution		PipelineTotal
 (In thousands)
At December 31, 2025
$506 $1,443 $— $1,949 
Current expected credit loss provision952 1,670 — 2,622 
Less write-offs charged against the allowance1,066 1,098 — 2,164 
Credit loss recoveries collected188 272 — 460 
At March 31, 2026$580 $2,287 $— $2,867 
ElectricNatural gas
distribution		PipelineTotal
 (In thousands)
At December 31, 2024
$473 $1,366 $— $1,839 
Current expected credit loss provision939 2,213 — 3,152 
Less write-offs charged against the allowance1,036 1,269 — 2,305 
Credit loss recoveries collected166 252 — 418 
At March 31, 2025$542 $2,562 $— $3,104 
v3.26.1
Inventories and natural gas in storage
 3 Months Ended
Mar. 31, 2026
Inventory Disclosure [Abstract]  
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. The portion of the cost of natural gas in storage expected to be used within 12 months was included in inventories. Inventories on the Consolidated Balance Sheets were as follows:
 March 31, 2026March 31, 2025December 31, 2025
 (In thousands)
Natural gas in storage (current)$14,796 $13,579 $34,333 
Fuel stock4,689 4,878 4,719 
Total$19,485 $18,457 $39,052 
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 $47.8 million, $48.5 million and $47.8 million at March 31, 2026 and 2025 and December 31, 2025, respectively.
v3.26.1
Earnings per share
 3 Months Ended
Mar. 31, 2026
Earnings Per Share [Abstract]  
Earnings per share Earnings per share
Basic earnings per share is computed by dividing net income by the weighted average number of shares of common stock outstanding during the applicable period. Diluted earnings per share is computed by dividing net income by the total of the weighted average number of shares of common stock outstanding during the applicable period, plus the effect of non-vested performance share awards and restricted stock units, as well as potentially issuable shares pursuant to FSAs using the treasury stock method. Net income was the same for both the basic and diluted earnings per share calculations. A reconciliation of the weighted average common shares outstanding used in the basic and diluted earnings per share calculations follows:
Three Months Ended
March 31,
20262025
(In thousands, except per share amounts)
Weighted average common shares outstanding - basic205,438 204,142 
Effect of dilutive performance share awards and restricted stock units1,556 817 
Weighted average common shares outstanding - diluted206,994 204,959 
Earnings per share - basic:
Income from continuing operations$.39 $.40 
Discontinued operations, net of tax— — 
Earnings per share - basic$.39 $.40 
Earnings per share - diluted:
Income from continuing operations$.39 $.40 
Discontinued operations, net of tax— — 
Earnings per share - diluted$.39 $.40 
Shares excluded from the calculation of diluted earnings per share50 — 
Dividends declared per common share$.14 $.13 
v3.26.1
Equity
 3 Months Ended
Mar. 31, 2026
Equity [Abstract]  
Equity Equity
At-the-market offering program On August 7, 2025, the Company entered into an EDA pursuant to which it may issue, offer, and sell, from time to time, up to an aggregate gross sales price of $400.0 million of shares of its common stock through an ATM offering program, which includes the ability to enter into FSAs. Since the establishment of the ATM offering program, the Company did not issue common stock pursuant to the EDA nor enter into any FSAs related to the EDA.

Equity forward sale agreements On December 5, 2025, the Company completed a follow-on public offering of 10,152,284 shares of the Company's common stock at a public offering price of $19.70 per share. In addition, on December 23, 2025, the underwriters exercised their option to purchase 1,522,842 additional shares of common stock. Pursuant to the FSAs entered into in connection with the offering, the Company has discretion to settle the FSAs on one or more settlement dates prior to December 6, 2027, subject to certain price adjustments as set forth in the FSAs as well as adjustments for transaction and other associated fees. The FSAs will be physically settled with shares of common stock issued by the Company, unless the Company elects to settle the FSAs in net cash or net shares, subject to certain conditions. If the Company elects to physically settle the FSAs, the Company will physically issue shares of common stock to the banking counterparties at the then-applicable forward sale price and receive proceeds at that time.
In March 2026, the Company partially settled the FSAs with physical delivery of 4.3 million shares of common stock to the counterparties in exchange for cash of $81.3 million. At March 31, 2026, the Company could have settled all of its outstanding FSAs with physical delivery of 7,375,126 shares of common stock to the banking counterparties in exchange for cash of approximately $139.6 million. If the FSAs had been net cash or net share settled at March 31, 2026, the Company estimates that the counterparties, in aggregate, would have been entitled to a net settlement of $13.2 million or 635,500 shares, respectively.
The forward price used to determine amounts due at settlement is calculated based on the public offering price, subject to transaction and other associated fees, adjusted by the overnight bank funding rate, less a spread, and less expected dividends on the Company's common stock during the period the FSAs are outstanding.
The FSAs are indexed to the Company's stock and meet the other requirements for equity classification. As a result of the equity classification, no gain or loss is recognized in earnings associated with the subsequent changes in fair value of the FSAs. Stockholders' equity equal to cash proceeds net of deferred issuance costs were and will be recorded upon settlement.
FSAs earnings per share dilution Prior to settlement, the potentially issuable shares pursuant to the FSAs will be reflected in the Company's diluted earnings per share calculation using the treasury stock method. Share dilution occurs when the average market price of the Company's stock during the reporting period is higher than the then-applicable forward sale price at the end of the reporting period. For more information on earnings per share, see Note 7.
v3.26.1
Revenue from contracts with customers
 3 Months Ended
Mar. 31, 2026
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.
Under 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.
The Company recognizes revenue from the sale of emissions allowances allocated under the environmental programs in certain states. The Company has the right to payment when the allowances are sold at auction. Revenue is recognized on a point in time basis within the quarter that the auction is held. The revenues associated with the sale of these allowances are deferred as a component of the respective jurisdiction’s regulatory liability for environmental compliance. For more information on the Company’s regulatory assets and liabilities, see Note 10.
Disaggregation
In the following tables, 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 14.
Three Months Ended March 31, 2026ElectricNatural gas
distribution		PipelineOtherTotal
(In thousands)
Residential utility sales$39,401 $246,326 $— $— $285,727 
Commercial utility sales1
49,184 157,368 — — 206,552 
Industrial utility sales10,010 12,412 — — 22,422 
Other utility sales1,960 — — — 1,960 
Natural gas transportation— 17,506 49,077 — 66,583 
Natural gas storage— — 5,467 — 5,467 
Other22,264 20,550 2,504 199 45,517 
Intersegment eliminations(167)(89)(34,460)(199)(34,915)
Revenues from contracts with customers122,652 454,073 22,588 — 599,313 
Other revenues(1,634)8,274 24 — 6,664 
Total external operating revenues$121,018 $462,347 $22,612 $— $605,977 
1Commercial utility sales includes the impact from data centers at the electric segment.
Three Months Ended March 31, 2025ElectricNatural gas
distribution		PipelineOtherTotal
(In thousands)
Residential utility sales$39,685 $289,235 $— $— $328,920 
Commercial utility sales1
48,477 192,331 — — 240,808 
Industrial utility sales9,164 15,462 — — 24,626 
Other utility sales1,850 — — — 1,850 
Natural gas transportation— 17,710 49,253 — 66,963 
Natural gas storage— — 6,030 — 6,030 
Other17,591 23,478 1,362 179 42,610 
Intersegment eliminations(178)(94)(33,337)(178)(33,787)
Revenues from contracts with customers116,589 538,122 23,308 1 678,020 
Other revenues(4,328)1,126 15 — (3,187)
Total external operating revenues$112,261 $539,248 $23,323 $1 $674,833 
1Commercial utility sales includes the impact from data centers at the electric segment.
Three Months Ended March 31, 2026ElectricNatural gas
distribution		PipelineOtherTotal
Three Months Ended March 31, 2025ElectricNatural gas
distribution		PipelineOtherTotal
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, storage 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 four years and one year, respectively.
At March 31, 2026, the Company expects to recognize revenue in future periods from remaining performance obligations, as follows:
12 months or lessNext 13-24 months25 months or moreTotal
(In millions)
$85.4 $78.4 $346.4 $510.2 
v3.26.1
Regulatory matters
 3 Months Ended
Mar. 31, 2026
Regulatory Assets and Liabilities Disclosure [Abstract]  
Regulatory matters Regulatory matters
Regulatory assets and liabilities
The following table summarizes the individual components of unamortized regulatory assets and liabilities:
Estimated
Recovery or Refund
Period as of
March 31, 2026
*March 31, 2026March 31, 2025December 31, 2025
(In thousands)
Regulatory assets:
Current:
Environmental compliance programs
Up to 1 year
$92,143 $56,441 $78,784 
Conservation programs
Up to 1 year
29,078 16,902 29,148 
Natural gas costs recoverable through rate adjustments
Up to 1 year
23,899 51,321 22,897 
Decoupling mechanisms
Up to 1 year
22,497 4,769 17,091 
Cost recovery mechanisms
Up to 1 year
15,327 4,806 13,460 
Electric fuel and purchased power deferral
Up to 1 year
3,163 7,109 6,902 
Other
Up to 1 year
4,572 1,993 11,297 
190,679 143,341 179,579 
Noncurrent:
Pension and postretirement benefits**135,222 142,065 135,222 
Cost recovery mechanisms
Up to 23 years
61,151 72,764 63,328 
Plant costs/asset retirement obligationsOver plant lives48,002 46,920 48,352 
Manufactured gas plant site remediation-28,466 27,443 28,411 
Taxes recoverable from customersOver plant lives12,145 12,228 12,250 
Covid-19 deferred costs
Up to 2 years
3,637 3,926 3,761 
Long-term debt refinancing costs
Up to 37 years
1,657 1,865 1,799 
Other
Up to 13 years
3,693 4,797 4,095 
293,973 312,008 297,218 
Total regulatory assets$484,652 $455,349 $476,797 
Estimated
Recovery or Refund
Period as of
March 31, 2026
*March 31, 2026March 31, 2025December 31, 2025
(In thousands)
Regulatory liabilities:
Current:
Environmental compliance programs
Up to 1 year
$90,692 $65,680 $89,306 
Natural gas costs refundable through rate adjustments
Up to 1 year
35,288 46,744 47,130 
Demand Charges
Up to 1 year
9,684 10,000 — 
Margin sharing
Up to 1 year
3,895 3,562 3,946 
Taxes refundable to customers
Up to 1 year
2,228 2,087 2,301 
Conservation programs
Up to 1 year
1,103 2,782 733 
Provision for rate refund
Up to 1 year
1,062 3,833 1,780 
Other
Up to 1 year
4,457 5,477 3,388 
148,409 140,165 148,584 
Noncurrent:
Plant removal and decommissioning costsOver plant lives227,100 221,349 224,313 
Taxes refundable to customersOver plant lives173,860 182,742 176,665 
Cost recovery mechanisms
Up to 16 years
43,896 33,373 41,323 
Accumulated deferred investment tax creditOver plant lives22,607 19,301 22,663 
Pension and postretirement benefits**4,776 4,862 4,776 
Other
Up to 12 years
2,718 2,252 2,589 
474,957 463,879 472,329 
Total regulatory liabilities$623,366 $604,044 $620,913 
Net regulatory position$(138,714)$(148,695)$(144,116)
*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 March 31, 2026 and 2025, and December 31, 2025, approximately $175.7 million, $179.3 million and $174.3 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, estimated future cost of manufactured gas plant site remediation and certain pipeline integrity cost recovery mechanisms.
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 in certain states. 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.
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.
Regulatory proceedings
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 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.
The following table summarizes the Company's significant regulatory proceedings and cases by jurisdiction:
SegmentStateFiling DateAnnual Revenue Increase (%) *
Annual Revenue Increase
(In millions) *
ROEStatusKey Drivers and Additional Information
General Rate Cases Pending
ElectricMontanaSeptember 30, 202520.2 %$14.1 10.8 %
Pending
Interim rate increase of $10.4M or 16.2% effective April 1, 2026
•Investments, including Badger Wind Farm
•Corresponding depreciation on those investments
•Increased operation and maintenance expense
Natural Gas DistributionOregonNovember 25, 202515.8 %$16.4 10.4 %Pending
•Rate base growth
•Growth in operations and maintenance expense
•Growth in depreciation expense associated with new investments in rate base
General Rate Cases Finalized
Natural Gas DistributionWashingtonMarch 29, 2024
Rate Year 1

7.9%



Rate Year 2

2.6%
Rate Year 1

$29.8



Rate Year 2

$10.8
9.5 %
Approved February 24, 2025
Final rates effective March 5, 2025
$3.7M revenue reduction effective June 1, 2025**

Final rates effective March 1, 2026
Filed for a $2.1M revenue reduction effective June 1, 2026**
•Multi-year rate case
•Infrastructure investments necessary to provide safe and reliable service
•Higher operating costs due to inflation
•$3.7M revenue reduction was driven by forecasted plant that was not placed in service by December 31, 2024
•$2.1M revenue reduction was driven by forecasted plant that was not placed in service by December 31, 2025
ElectricWyomingJune 30, 202518.6 %$5.8 9.7 %
Approved
Final rates effective April 1, 2026
•Increases in operation and maintenance expense
•Investments made since the last rate case
•Corresponding depreciation on those infrastructure investments
•Withdrew the requested Reliability and Safety Rider
*Annual revenue increase and percent increase for general rate cases pending and general rate cases finalized, reflects the final approved amount or the amount reflected in the most recent settlement agreement, if applicable.
**Reflects a reduction to revenues resulting from a provisional plant review. The adjustment applies retroactively to the original rate effective date. As a result, the Company is required to refund customers for amounts overcollected during the retroactive period.
SegmentStateFiling Date
Annual Revenue Increase
(In millions)
StatusKey Drivers and Additional Information
Other Filings
Natural Gas DistributionWyomingAugust 15, 2025N/APending
System Safety and Integrity Rider
•Would allow Montana-Dakota to recover costs and expenses associated with a pipeline replacement program
ElectricMontanaSeptember 30, 2025N/APending
Systems Management Cost Adjustment Mechanism
•Recovery of transmission and wildfire related costs
ElectricSouth DakotaOctober 31, 2025$1.1 Pending
Infrastructure Rider
•Allows annual adjustments for recent projected capital costs and related expenses for projects determined to be recoverable
•Update includes Badger Wind Farm
v3.26.1
Environmental allowances and obligations
 3 Months Ended
Mar. 31, 2026
Accounting Policies [Abstract]  
Environmental allowances and obligations Environmental allowances and obligations
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 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.
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 10.
v3.26.1
Fair value measurements
 3 Months Ended
Mar. 31, 2026
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 $65.7 million, $61.1 million and $67.4 million, at March 31, 2026 and 2025, and December 31, 2025, respectively, are classified as Investments on the Consolidated Balance Sheets. The net unrealized loss on these investments was $505,000 and $470,000 for the three months ended March 31, 2026 and 2025, respectively. 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 2026 and second quarter of 2025, the Company withdrew $4.0 million and $5.0 million, respectively, of cash in excess of 125 percent of the full funding amount, which had no effect on the cost basis of the investments held.
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:
March 31, 2026CostGross
Unrealized
Gains		Gross
Unrealized
Losses		Fair Value
(In thousands)
Mortgage-backed securities$8,382 $9 $224 $8,167 
U.S. Treasury securities3,679 32 3 3,708 
Total$12,061 $41 $227 $11,875 
March 31, 2025CostGross
Unrealized
Gains		Gross
Unrealized
Losses		Fair Value
(In thousands)
Mortgage-backed securities$7,997 $18 $299 $7,716 
U.S. Treasury securities3,869 76 1 3,944 
Total$11,866 $94 $300 $11,660 
December 31, 2025CostGross
Unrealized
Gains		Gross
Unrealized
Losses		Fair Value
(In thousands)
Mortgage-backed securities$8,539 $28 $204 $8,363 
U.S. Treasury securities3,992 33 — 4,025 
Total$12,531 $61 $204 $12,388 
The Company's assets measured at fair value on a recurring basis were as follows:
 Fair Value Measurements at March 31, 2026, Using 
 Quoted Prices in
Active Markets
for Identical
Assets
(Level 1)		Significant
Other
Observable
Inputs
(Level 2)		Significant
Unobservable
Inputs
(Level 3)		Balance at March 31, 2026
(In thousands)
Assets:    
Money market funds$— $9,104 $— $9,104 
Insurance contracts*— 65,657 — 65,657 
Available-for-sale securities:
Mortgage-backed securities— 8,167 — 8,167 
U.S. Treasury securities— 3,708 — 3,708 
Total assets measured at fair value$— $86,636 $— $86,636 
* The insurance contracts invest approximately 54 percent in fixed-income investments, 19 percent in common stock of large-cap companies, 10 percent in target date investments, 8 percent in common stock of mid-cap companies, 4 percent in common stock of small-cap companies, 3 percent in cash equivalents, 1 percent in international investments, and 1 percent in real estate.
 Fair Value Measurements at March 31, 2025, Using 
 Quoted Prices in
Active Markets
for Identical
Assets
(Level 1)		Significant
Other
Observable
Inputs
(Level 2)		Significant
Unobservable
Inputs
(Level 3)		Balance at March 31, 2025
(In thousands)
Assets:    
Money market funds$— $13,841 $— $13,841 
Insurance contracts*— 61,075 — 61,075 
Available-for-sale securities:
Mortgage-backed securities— 7,716 — 7,716 
U.S. Treasury securities— 3,944 — 3,944 
Total assets measured at fair value$— $86,576 $— $86,576 
* The insurance contracts invest approximately 58 percent in fixed-income investments, 17 percent in common stock of large-cap companies, 9 percent in target date investments, 7 percent in common stock of mid-cap companies, 4 percent in common stock of small-cap companies, 3 percent in cash equivalents, 1 percent in international investments, and 1 percent in real estate.
 Fair Value Measurements at December 31, 2025, Using 
Quoted Prices in
Active Markets
for Identical
Assets
 (Level 1)		Significant
Other
Observable
Inputs
(Level 2)		Significant
Unobservable
Inputs
 (Level 3)		Balance at December 31, 2025
(In thousands)
Assets:    
Money market funds$— $9,839 $— $9,839 
Insurance contracts*— 67,409 — 67,409 
Available-for-sale securities:
Mortgage-backed securities— 8,363 — 8,363 
U.S. Treasury securities— 4,025 — 4,025 
Total assets measured at fair value$— $89,636 $— $89,636 
* The insurance contracts invest approximately 57 percent in fixed-income investments, 18 percent in common stock of large-cap companies, 10 percent in target date investments, 7 percent in common stock of mid-cap companies, 4 percent in common stock of small-cap companies, 3 percent in cash equivalents, 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 was as follows:
 March 31, 2026March 31, 2025December 31, 2025
(In thousands)
Carrying amount$2,595,996 $2,193,676 $2,676,855 
Fair value$2,283,864 $1,902,217 $2,385,170 
The carrying amounts of the Company's remaining financial instruments included in current assets and current liabilities approximate their fair values.
v3.26.1
Debt
 3 Months Ended
Mar. 31, 2026
Debt Disclosure [Abstract]  
Debt Debt
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. The Company and its subsidiaries were in compliance with applicable covenants at March 31, 2026. 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.

Credit facilities
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 Company's borrowings under the commercial paper program and revolving credit agreements are classified as long-term debt as they are intended to be refinanced on a long-term basis through continued borrowings. All of the credit agreements contain customary covenants and provisions, including covenants 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 restrictions on the sale of certain assets, limitations on indebtedness and the making of certain investments.
The following table summarizes the outstanding revolving credit facilities of the Company and its subsidiaries:

Company
Debt-to-Total Capitalization Ratio at March 31, 2026
Provisions for Increased Borrowings, up to a maximum of:Facility
Limit		Amount Outstanding at March 31, 2026Amount Outstanding at March 31, 2025Amount Outstanding at December 31, 2025Letters of Credit at March 31, 2026Expiration
Date
(In millions)
Montana-Dakota Utilities Co.51 %$250.0 $200.0 $104.6 $51.1 $132.0 $— 12/11/30
Cascade Natural Gas Corporation50 %$225.0 $175.0 $124.3 $21.4 $96.5 $2.2 12/11/30
Intermountain Gas Company51 %$225.0 $175.0 $59.8 $83.5 $67.3 $— 12/11/30
MDU Resources Group, Inc.47 %$250.0 $200.0 $43.5 $— $32.9 $1.0 12/11/30

Long-term Debt Outstanding Long-term debt outstanding was as follows:
 
Weighted
Average
Interest
Rate at
March 31, 2026
March 31, 2026March 31, 2025December 31, 2025
 (In thousands)
Senior Notes due on dates ranging from July 15, 2026 to June 15, 2062
4.83 %$2,110,000 $1,947,000 $2,010,000 
Credit agreements due on December 11, 20305.47 %227,600 104,900 196,700 
Term Loan Agreements due on dates ranging from January 31, 2027 to April 1, 20394.04 %126,900 61,600 310,900 
Commercial paper supported by revolving credit agreement4.16 %104,617 51,100 132,000 
Medium-Term Notes due on dates ranging from September 15, 2027 to March 16, 2029
7.32 %35,000 35,000 35,000 
Other notes due on November 30, 2038
6.00 %324 342 329 
Less unamortized debt issuance costs8,445 6,266 8,074 
Total long-term debt2,595,996 2,193,676 2,676,855 
Less current maturities214,700 161,700 144,700 
Net long-term debt$2,381,296 $2,031,976 $2,532,155 

Montana-Dakota On October 28, 2025, Montana-Dakota entered into a NPA to issue $250.0 million of senior notes, with maturity dates of October 28, 2035, October 28, 2040, and February 2, 2056, at a weighted average interest rate of 5.96 percent. On October 28, 2025, Montana-Dakota issued $150.0 million in senior notes under the NPA with the remaining $100.0 million issued on February 2, 2026. 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. Other covenants include a minimum interest coverage ratio and restrictions on the sale of certain assets.

On December 30, 2025, Montana-Dakota entered into a $250.0 million term loan agreement with a SOFR-based variable interest rate and a maturity date of January 29, 2027. In February 2026 and March 2026, Montana-Dakota paid down $100.0 million and $80.0 million of the outstanding balance under the term loan agreement, respectively. 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.

WBI Energy Transmission On January 15, 2026, WBI Energy Transmission extended its $350.0 million uncommitted note purchase and private shelf agreement from December 22, 2025 to December 22, 2028, unless either party terminates such issuance right. WBI Energy Transmission had $235.0 million of notes outstanding at March 31, 2026, which reduced the remaining capacity under this uncommitted private shelf agreement to $115.0 million. The principal amount and interest rate of any series of shelf notes will be determined at the applicable time of issuance and purchase.

WBI Energy Transmission's ratio of total debt to total capitalization at March 31, 2026 was 39 percent.
v3.26.1
Business segment data
 3 Months Ended
Mar. 31, 2026
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 units 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 the 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 and other coverages. In addition, the Other category includes certain assets, liabilities and tax adjustments of the holding company primarily associated with corporate functions. Also included are certain general and administrative costs (reflected in operation and maintenance expense) and interest expense, which were previously allocated to the Company's former businesses which do not meet the criteria for discontinued operations.
Discontinued operations includes certain costs associated with legacy business activities 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 of the Notes to Consolidated Financial Statements in the 2025 Annual Report. Information on the Company's segments was as follows:
Three Months Ended March 31, 2026ElectricNatural gas distributionPipelineOtherConsolidated
Three Months Ended March 31, 2025ElectricNatural gas distributionPipelineOtherConsolidated
Three Months Ended March 31, 2026ElectricNatural gas distributionPipelineOtherConsolidated
(In thousands)
Operating revenues:
External operating revenues$121,018 $462,347 $22,612 $— $605,977 
Intersegment operating revenues167 89 34,460 199 34,915 
Purchased natural gas sold:
External purchased natural gas sold— 239,391 — — 239,391 
Intersegment purchased natural gas sold— 34,420 — — 34,420 
Electric fuel and purchased power46,067 — — — 46,067 
Operation and maintenance:
External operation and maintenance28,705 65,126 20,769 305 114,905 
Intersegment operation and maintenance167 89 40 199 495 
Depreciation and amortization19,627 26,333 8,219 — 54,179 
Taxes, other than income5,520 26,452 3,758 — 35,730 
Other income:
External other income451 2,270 (423)307 2,605 
Intersegment other income— — 115 805 920 
Interest expense:
External interest expense11,911 16,286 3,102 1,386 32,685 
Intersegment interest expense— — 920 — 920 
Income tax (benefit) expense
(4,912)12,426 4,702 (7,538)4,678 
Income from continuing operations14,551 44,183 15,254 6,959 80,947 
Discontinued operations, net of tax— — — (130)(130)
Net income$14,551 $44,183 $15,254 $6,829 $80,817 
Three Months Ended March 31, 2025ElectricNatural gas distributionPipelineOtherConsolidated
(In thousands)
Operating revenues:
External operating revenues$112,261 $539,248 $23,323 $1 $674,833 
Intersegment operating revenues178 94 33,337 178 33,787 
Purchased natural gas sold:
External purchased natural gas sold— 317,157 — — 317,157 
Intersegment purchased natural gas sold— 33,323 — — 33,323 
Electric fuel and purchased power43,748 — — — 43,748 
Operation and maintenance:
External operation and maintenance28,407 63,484 19,239 (83)111,047 
Intersegment operation and maintenance178 94 14 178 464 
Depreciation and amortization17,183 26,122 7,956 — 51,261 
Taxes, other than income4,815 30,628 3,314 — 38,757 
Other income:
External other income992 3,301 307 397 4,997 
Intersegment other income— — 123 986 1,109 
Interest expense:
External interest expense7,887 14,876 3,121 938 26,822 
Intersegment interest expense— — 1,109 — 1,109 
Income tax (benefit) expense
(3,731)12,301 5,127 (5,126)8,571 
Income (loss) from continuing operations
14,944 44,658 17,210 5,655 82,467 
Discontinued operations, net of tax— — — (502)(502)
Net income$14,944 $44,658 $17,210 $5,153 $81,965 
A reconciliation of reportable segment operating revenues to consolidated operating revenues is as follows:
Three Months Ended
March 31,
2026 2025 
(In thousands)
Operating revenues reconciliation:
Total reportable segment operating revenues$640,693 $708,441 
Other revenue199 179 
Elimination of intersegment operating revenues(34,915)(33,787)
Total consolidated operating revenues$605,977 $674,833 
v3.26.1
Employee benefit plans
 3 Months Ended
Mar. 31, 2026
Retirement Benefits [Abstract]  
Employee benefit plans Employee benefit plans
Pension and other postretirement plans
The Company has noncontributory qualified defined benefit pension plans and other postretirement benefit plans for certain eligible employees.
Components of net periodic benefit cost for the Company's pension benefit plans were as follows:
Three Months Ended
March 31,
20262025
(In thousands)
Components of net periodic benefit cost:
Interest cost$3,128 $3,303 
Expected return on assets(3,391)(3,645)
Amortization of net actuarial loss1,432 1,193 
Net periodic benefit cost$1,169 $851 
Components of net periodic benefit credit for the Company's other postretirement benefit plans were as follows:
Three Months Ended
March 31,
20262025
(In thousands)
Components of net periodic benefit credit:
Service cost$94 $99 
Interest cost441 462 
Expected return on assets(1,270)(1,292)
Amortization of prior service credit(45)(290)
Amortization of net actuarial gain(23)(80)
Net periodic benefit credit, including amount capitalized(803)(1,101)
Less amount capitalized18 18 
Net periodic benefit credit$(821)$(1,119)
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. The service cost component is included in Operation and maintenance expense on the Consolidated Statements of Income.
Nonqualified defined 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. The Company's net periodic benefit cost for these plans was $662,000 and $716,000 for the three months ended March 31, 2026 and 2025, respectively. The components of net periodic benefit cost for these plans are included in Other income on the Consolidated Statements of Income.
v3.26.1
Commitments and contingencies
 3 Months Ended
Mar. 31, 2026
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 March 31, 2026 and 2025, and December 31, 2025, the Company accrued liabilities, which have not been discounted, of $24.9 million, $24.3 million and $26.1 million, respectively. The Company also recorded corresponding receivables of $83,000, $541,000, and $1.6 million, at March 31, 2026 and 2025, and December 31, 2025, respectively. The Company recorded regulatory assets of $23.0 million, $22.7 million and $23.2 million, at March 31, 2026 and 2025, and December 31, 2025, respectively, related to the accrued liabilities. The accruals are for contingencies resulting from litigation, regulatory 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. In January 2026, the Company received a final order on a regulatory commission complaint for $2.0 million, with $250,000 suspended on the condition that the Company complete additional compliance actions outlined in the order. At December 31, 2025, the Company had $1.75 million included in accrued liabilities, which was paid in February 2026.
Management believes that the outcomes with respect to probable and reasonably possible losses in excess of the amounts accrued, net of 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
The Company is a party to claims for the cleanup of environmental contamination at certain manufactured gas plant sites. There were no material changes to the Company's environmental matters that were previously reported in the 2025 Annual Report.
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 March 31, 2026, the fixed maximum amounts guaranteed under these letters of credit aggregated $3.2 million, all of which have scheduled expiration of the maximum amounts in 2026. There were no amounts outstanding under the previously mentioned letters of credit at March 31, 2026. 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 March 31, 2026, approximately $13.4 million of surety bonds were outstanding, which were not reflected on the Consolidated Balance Sheet.
Leases
The Company's leases primarily include operating leases for equipment, buildings, easements and vehicles. The Company leases certain equipment to third parties through its utility business, which are considered short-term operating leases with terms of less than 12 months. Lease revenue was not material for the three months ended March 31, 2026 or 2025. At March 31, 2026, the Company had no lease receivables.
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 March 31, 2026, 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 $23.0 million.
v3.26.1
Insider Trading Arrangements
 3 Months Ended
Mar. 31, 2026
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
v3.26.1
Basis of presentation (Policies)
 3 Months Ended
Mar. 31, 2026
Accounting Policies [Abstract]  
Basis of presentation
The accompanying consolidated interim financial statements were prepared in accordance with GAAP for interim financial information and with the instructions to Form 10-Q and Rule 10-01 of Regulation S-X. Interim financial statements do not include all disclosures provided in annual financial statements and, accordingly, these financial statements should be read in conjunction with those appearing in the 2025 Annual Report. The information is unaudited but includes all adjustments that are, in the opinion of management, necessary for a fair presentation of the accompanying consolidated interim financial statements and are of a normal recurring nature. Depreciation and amortization expense is reported separately on the Consolidated Statements of Income and therefore is excluded from the other line items within operating expenses.
Discontinued operations includes certain costs associated with legacy business activities other than certain general and administrative costs (reflected in operation and maintenance expense) and interest expense, which were previously allocated to the Company's former businesses which do not meet the criteria for discontinued operations. Discontinued operations are not material to the financial statements for any period presented. Unless otherwise indicated, the amounts presented in the accompanying condensed notes to the consolidated financial statements relate to the Company's continuing operations. For more information on discontinued operations, see Note 3.
Management has also evaluated the impact of events occurring after March 31, 2026, up to the date of issuance of these consolidated interim financial statements on May 7, 2026, that would require recognition or disclosure in the Consolidated Financial Statements.
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 issued accounting standards not yet adopted
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.
ASU 2025-05
Measurement of
Credit Losses for
Accounts Receivable
and Contract Assets
In July 2025, the FASB issued guidance on applying a practical expedient when estimating expected credit losses on current accounts receivable and/or current contract assets arising from transactions under ASC Topic 606 - Revenue from Contracts with Customers.
Effective for annual
reporting periods
beginning after December
15, 2025.
The Company is currently
evaluating the impact the guidance will have on its results of operations, financial position, cash flows, and disclosures for the year ended December 31, 2026.
ASU 2025-06
Targeted
Improvements to the Accounting of Internal-Use
Software
In September 2025, the FASB issued guidance on accounting for
capitalization of development costs for internal-use software under
ASC Subtopic 350-40 and the transition approaches to use.
Effective for annual reporting periods beginning after December
15, 2027.
The Company is currently
evaluating the impact the guidance will have on its results of operations, financial position, cash flows, and disclosures for the year ended December 31, 2028.
ASU 2025-10
Accounting for
Government Grants Received By Business Entities
In December 2025, the FASB issued guidance on accounting for government grants received by business entities that are related to an asset (purchase, construction, or acquisition of a long-lived asset or inventory) or income (reimbursements to a business entity for operating expenses).
Effective for annual reporting periods beginning after December
15, 2028.
The Company is currently
evaluating the impact the guidance will have on its results of operations, financial position, cash flows, and disclosures for the year ended December 31, 2029.
Discontinued operations
Discontinued operations includes certain costs associated with legacy business activities other than certain general and administrative costs (reflected in operation and maintenance expense) and interest expense, which were previously allocated to the company's former businesses which do not meet the criteria for discontinued operations.
Expected credit loss 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.
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.
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 applicable period. 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 applicable period, plus the effect of non-vested performance share awards and restricted stock units, as well as potentially issuable shares pursuant to FSAs using the treasury stock method.
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.
Under 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.
The Company recognizes revenue from the sale of emissions allowances allocated under the environmental programs in certain states. The Company has the right to payment when the allowances are sold at auction. Revenue is recognized on a point in time basis within the quarter that the auction is held. The revenues associated with the sale of these allowances are deferred as a component of the respective jurisdiction’s regulatory liability for environmental compliance.
Environmental allowances and obligations
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 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.
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.
Fair value measurements The Company measures its investments in certain fixed-income and equity securities at fair value with changes in fair value recognized in income.
Investments 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.
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 units 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.
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.
v3.26.1
Receivables and allowance for expected credit losses (Tables)
 3 Months Ended
Mar. 31, 2026
Credit Loss [Abstract]  
Schedule of Accounts Receivable, Allowance for Credit Loss
Details of the Company's expected credit losses were as follows:
ElectricNatural gas
distribution		PipelineTotal
 (In thousands)
At December 31, 2025
$506 $1,443 $— $1,949 
Current expected credit loss provision952 1,670 — 2,622 
Less write-offs charged against the allowance1,066 1,098 — 2,164 
Credit loss recoveries collected188 272 — 460 
At March 31, 2026$580 $2,287 $— $2,867 
ElectricNatural gas
distribution		PipelineTotal
 (In thousands)
At December 31, 2024
$473 $1,366 $— $1,839 
Current expected credit loss provision939 2,213 — 3,152 
Less write-offs charged against the allowance1,036 1,269 — 2,305 
Credit loss recoveries collected166 252 — 418 
At March 31, 2025$542 $2,562 $— $3,104 
v3.26.1
Inventories and natural gas in storage (Tables)
 3 Months Ended
Mar. 31, 2026
Inventory Disclosure [Abstract]  
Schedule of Inventories Inventories on the Consolidated Balance Sheets were as follows:
 March 31, 2026March 31, 2025December 31, 2025
 (In thousands)
Natural gas in storage (current)$14,796 $13,579 $34,333 
Fuel stock4,689 4,878 4,719 
Total$19,485 $18,457 $39,052 
v3.26.1
Earnings per share (Tables)
 3 Months Ended
Mar. 31, 2026
Earnings Per Share [Abstract]  
Schedule of Weighted Average Common Shares Outstanding A reconciliation of the weighted average common shares outstanding used in the basic and diluted earnings per share calculations follows:
Three Months Ended
March 31,
20262025
(In thousands, except per share amounts)
Weighted average common shares outstanding - basic205,438 204,142 
Effect of dilutive performance share awards and restricted stock units1,556 817 
Weighted average common shares outstanding - diluted206,994 204,959 
Earnings per share - basic:
Income from continuing operations$.39 $.40 
Discontinued operations, net of tax— — 
Earnings per share - basic$.39 $.40 
Earnings per share - diluted:
Income from continuing operations$.39 $.40 
Discontinued operations, net of tax— — 
Earnings per share - diluted$.39 $.40 
Shares excluded from the calculation of diluted earnings per share50 — 
Dividends declared per common share$.14 $.13 
v3.26.1
Revenue from contracts with customers (Tables)
 3 Months Ended
Mar. 31, 2026
Revenue from Contract with Customer [Abstract]  
Schedule of Disaggregation of revenue
In the following tables, 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 14.
Three Months Ended March 31, 2026ElectricNatural gas
distribution		PipelineOtherTotal
(In thousands)
Residential utility sales$39,401 $246,326 $— $— $285,727 
Commercial utility sales1
49,184 157,368 — — 206,552 
Industrial utility sales10,010 12,412 — — 22,422 
Other utility sales1,960 — — — 1,960 
Natural gas transportation— 17,506 49,077 — 66,583 
Natural gas storage— — 5,467 — 5,467 
Other22,264 20,550 2,504 199 45,517 
Intersegment eliminations(167)(89)(34,460)(199)(34,915)
Revenues from contracts with customers122,652 454,073 22,588 — 599,313 
Other revenues(1,634)8,274 24 — 6,664 
Total external operating revenues$121,018 $462,347 $22,612 $— $605,977 
1Commercial utility sales includes the impact from data centers at the electric segment.
Three Months Ended March 31, 2025ElectricNatural gas
distribution		PipelineOtherTotal
(In thousands)
Residential utility sales$39,685 $289,235 $— $— $328,920 
Commercial utility sales1
48,477 192,331 — — 240,808 
Industrial utility sales9,164 15,462 — — 24,626 
Other utility sales1,850 — — — 1,850 
Natural gas transportation— 17,710 49,253 — 66,963 
Natural gas storage— — 6,030 — 6,030 
Other17,591 23,478 1,362 179 42,610 
Intersegment eliminations(178)(94)(33,337)(178)(33,787)
Revenues from contracts with customers116,589 538,122 23,308 1 678,020 
Other revenues(4,328)1,126 15 — (3,187)
Total external operating revenues$112,261 $539,248 $23,323 $1 $674,833 
1Commercial utility sales includes the impact from data centers at the electric segment.
Three Months Ended March 31, 2026ElectricNatural gas
distribution		PipelineOtherTotal
Three Months Ended March 31, 2025ElectricNatural gas
distribution		PipelineOtherTotal
Schedule of Remaining Performance Obligations
At March 31, 2026, the Company expects to recognize revenue in future periods from remaining performance obligations, as follows:
12 months or lessNext 13-24 months25 months or moreTotal
(In millions)
$85.4 $78.4 $346.4 $510.2 
v3.26.1
Regulatory matters (Tables)
 3 Months Ended
Mar. 31, 2026
Regulatory Assets and Liabilities Disclosure [Abstract]  
Schedule of Regulatory Assets
The following table summarizes the individual components of unamortized regulatory assets and liabilities:
Estimated
Recovery or Refund
Period as of
March 31, 2026
*March 31, 2026March 31, 2025December 31, 2025
(In thousands)
Regulatory assets:
Current:
Environmental compliance programs
Up to 1 year
$92,143 $56,441 $78,784 
Conservation programs
Up to 1 year
29,078 16,902 29,148 
Natural gas costs recoverable through rate adjustments
Up to 1 year
23,899 51,321 22,897 
Decoupling mechanisms
Up to 1 year
22,497 4,769 17,091 
Cost recovery mechanisms
Up to 1 year
15,327 4,806 13,460 
Electric fuel and purchased power deferral
Up to 1 year
3,163 7,109 6,902 
Other
Up to 1 year
4,572 1,993 11,297 
190,679 143,341 179,579 
Noncurrent:
Pension and postretirement benefits**135,222 142,065 135,222 
Cost recovery mechanisms
Up to 23 years
61,151 72,764 63,328 
Plant costs/asset retirement obligationsOver plant lives48,002 46,920 48,352 
Manufactured gas plant site remediation-28,466 27,443 28,411 
Taxes recoverable from customersOver plant lives12,145 12,228 12,250 
Covid-19 deferred costs
Up to 2 years
3,637 3,926 3,761 
Long-term debt refinancing costs
Up to 37 years
1,657 1,865 1,799 
Other
Up to 13 years
3,693 4,797 4,095 
293,973 312,008 297,218 
Total regulatory assets$484,652 $455,349 $476,797 
Estimated
Recovery or Refund
Period as of
March 31, 2026
*March 31, 2026March 31, 2025December 31, 2025
(In thousands)
Regulatory liabilities:
Current:
Environmental compliance programs
Up to 1 year
$90,692 $65,680 $89,306 
Natural gas costs refundable through rate adjustments
Up to 1 year
35,288 46,744 47,130 
Demand Charges
Up to 1 year
9,684 10,000 — 
Margin sharing
Up to 1 year
3,895 3,562 3,946 
Taxes refundable to customers
Up to 1 year
2,228 2,087 2,301 
Conservation programs
Up to 1 year
1,103 2,782 733 
Provision for rate refund
Up to 1 year
1,062 3,833 1,780 
Other
Up to 1 year
4,457 5,477 3,388 
148,409 140,165 148,584 
Noncurrent:
Plant removal and decommissioning costsOver plant lives227,100 221,349 224,313 
Taxes refundable to customersOver plant lives173,860 182,742 176,665 
Cost recovery mechanisms
Up to 16 years
43,896 33,373 41,323 
Accumulated deferred investment tax creditOver plant lives22,607 19,301 22,663 
Pension and postretirement benefits**4,776 4,862 4,776 
Other
Up to 12 years
2,718 2,252 2,589 
474,957 463,879 472,329 
Total regulatory liabilities$623,366 $604,044 $620,913 
Net regulatory position$(138,714)$(148,695)$(144,116)
*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:
Estimated
Recovery or Refund
Period as of
March 31, 2026
*March 31, 2026March 31, 2025December 31, 2025
(In thousands)
Regulatory assets:
Current:
Environmental compliance programs
Up to 1 year
$92,143 $56,441 $78,784 
Conservation programs
Up to 1 year
29,078 16,902 29,148 
Natural gas costs recoverable through rate adjustments
Up to 1 year
23,899 51,321 22,897 
Decoupling mechanisms
Up to 1 year
22,497 4,769 17,091 
Cost recovery mechanisms
Up to 1 year
15,327 4,806 13,460 
Electric fuel and purchased power deferral
Up to 1 year
3,163 7,109 6,902 
Other
Up to 1 year
4,572 1,993 11,297 
190,679 143,341 179,579 
Noncurrent:
Pension and postretirement benefits**135,222 142,065 135,222 
Cost recovery mechanisms
Up to 23 years
61,151 72,764 63,328 
Plant costs/asset retirement obligationsOver plant lives48,002 46,920 48,352 
Manufactured gas plant site remediation-28,466 27,443 28,411 
Taxes recoverable from customersOver plant lives12,145 12,228 12,250 
Covid-19 deferred costs
Up to 2 years
3,637 3,926 3,761 
Long-term debt refinancing costs
Up to 37 years
1,657 1,865 1,799 
Other
Up to 13 years
3,693 4,797 4,095 
293,973 312,008 297,218 
Total regulatory assets$484,652 $455,349 $476,797 
Estimated
Recovery or Refund
Period as of
March 31, 2026
*March 31, 2026March 31, 2025December 31, 2025
(In thousands)
Regulatory liabilities:
Current:
Environmental compliance programs
Up to 1 year
$90,692 $65,680 $89,306 
Natural gas costs refundable through rate adjustments
Up to 1 year
35,288 46,744 47,130 
Demand Charges
Up to 1 year
9,684 10,000 — 
Margin sharing
Up to 1 year
3,895 3,562 3,946 
Taxes refundable to customers
Up to 1 year
2,228 2,087 2,301 
Conservation programs
Up to 1 year
1,103 2,782 733 
Provision for rate refund
Up to 1 year
1,062 3,833 1,780 
Other
Up to 1 year
4,457 5,477 3,388 
148,409 140,165 148,584 
Noncurrent:
Plant removal and decommissioning costsOver plant lives227,100 221,349 224,313 
Taxes refundable to customersOver plant lives173,860 182,742 176,665 
Cost recovery mechanisms
Up to 16 years
43,896 33,373 41,323 
Accumulated deferred investment tax creditOver plant lives22,607 19,301 22,663 
Pension and postretirement benefits**4,776 4,862 4,776 
Other
Up to 12 years
2,718 2,252 2,589 
474,957 463,879 472,329 
Total regulatory liabilities$623,366 $604,044 $620,913 
Net regulatory position$(138,714)$(148,695)$(144,116)
*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 Proceedings
The following table summarizes the Company's significant regulatory proceedings and cases by jurisdiction:
SegmentStateFiling DateAnnual Revenue Increase (%) *
Annual Revenue Increase
(In millions) *
ROEStatusKey Drivers and Additional Information
General Rate Cases Pending
ElectricMontanaSeptember 30, 202520.2 %$14.1 10.8 %
Pending
Interim rate increase of $10.4M or 16.2% effective April 1, 2026
•Investments, including Badger Wind Farm
•Corresponding depreciation on those investments
•Increased operation and maintenance expense
Natural Gas DistributionOregonNovember 25, 202515.8 %$16.4 10.4 %Pending
•Rate base growth
•Growth in operations and maintenance expense
•Growth in depreciation expense associated with new investments in rate base
General Rate Cases Finalized
Natural Gas DistributionWashingtonMarch 29, 2024
Rate Year 1

7.9%



Rate Year 2

2.6%
Rate Year 1

$29.8



Rate Year 2

$10.8
9.5 %
Approved February 24, 2025
Final rates effective March 5, 2025
$3.7M revenue reduction effective June 1, 2025**

Final rates effective March 1, 2026
Filed for a $2.1M revenue reduction effective June 1, 2026**
•Multi-year rate case
•Infrastructure investments necessary to provide safe and reliable service
•Higher operating costs due to inflation
•$3.7M revenue reduction was driven by forecasted plant that was not placed in service by December 31, 2024
•$2.1M revenue reduction was driven by forecasted plant that was not placed in service by December 31, 2025
ElectricWyomingJune 30, 202518.6 %$5.8 9.7 %
Approved
Final rates effective April 1, 2026
•Increases in operation and maintenance expense
•Investments made since the last rate case
•Corresponding depreciation on those infrastructure investments
•Withdrew the requested Reliability and Safety Rider
*Annual revenue increase and percent increase for general rate cases pending and general rate cases finalized, reflects the final approved amount or the amount reflected in the most recent settlement agreement, if applicable.
**Reflects a reduction to revenues resulting from a provisional plant review. The adjustment applies retroactively to the original rate effective date. As a result, the Company is required to refund customers for amounts overcollected during the retroactive period.
SegmentStateFiling Date
Annual Revenue Increase
(In millions)
StatusKey Drivers and Additional Information
Other Filings
Natural Gas DistributionWyomingAugust 15, 2025N/APending
System Safety and Integrity Rider
•Would allow Montana-Dakota to recover costs and expenses associated with a pipeline replacement program
ElectricMontanaSeptember 30, 2025N/APending
Systems Management Cost Adjustment Mechanism
•Recovery of transmission and wildfire related costs
ElectricSouth DakotaOctober 31, 2025$1.1 Pending
Infrastructure Rider
•Allows annual adjustments for recent projected capital costs and related expenses for projects determined to be recoverable
•Update includes Badger Wind Farm
v3.26.1
Fair value measurements (Tables)
 3 Months Ended
Mar. 31, 2026
Fair Value Disclosures [Abstract]  
Schedule of Available-for-Sale Securities Details of available-for-sale securities were as follows:
March 31, 2026CostGross
Unrealized
Gains		Gross
Unrealized
Losses		Fair Value
(In thousands)
Mortgage-backed securities$8,382 $9 $224 $8,167 
U.S. Treasury securities3,679 32 3 3,708 
Total$12,061 $41 $227 $11,875 
March 31, 2025CostGross
Unrealized
Gains		Gross
Unrealized
Losses		Fair Value
(In thousands)
Mortgage-backed securities$7,997 $18 $299 $7,716 
U.S. Treasury securities3,869 76 1 3,944 
Total$11,866 $94 $300 $11,660 
December 31, 2025CostGross
Unrealized
Gains		Gross
Unrealized
Losses		Fair Value
(In thousands)
Mortgage-backed securities$8,539 $28 $204 $8,363 
U.S. Treasury securities3,992 33 — 4,025 
Total$12,531 $61 $204 $12,388 
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis
The Company's assets measured at fair value on a recurring basis were as follows:
 Fair Value Measurements at March 31, 2026, Using 
 Quoted Prices in
Active Markets
for Identical
Assets
(Level 1)		Significant
Other
Observable
Inputs
(Level 2)		Significant
Unobservable
Inputs
(Level 3)		Balance at March 31, 2026
(In thousands)
Assets:    
Money market funds$— $9,104 $— $9,104 
Insurance contracts*— 65,657 — 65,657 
Available-for-sale securities:
Mortgage-backed securities— 8,167 — 8,167 
U.S. Treasury securities— 3,708 — 3,708 
Total assets measured at fair value$— $86,636 $— $86,636 
* The insurance contracts invest approximately 54 percent in fixed-income investments, 19 percent in common stock of large-cap companies, 10 percent in target date investments, 8 percent in common stock of mid-cap companies, 4 percent in common stock of small-cap companies, 3 percent in cash equivalents, 1 percent in international investments, and 1 percent in real estate.
 Fair Value Measurements at March 31, 2025, Using 
 Quoted Prices in
Active Markets
for Identical
Assets
(Level 1)		Significant
Other
Observable
Inputs
(Level 2)		Significant
Unobservable
Inputs
(Level 3)		Balance at March 31, 2025
(In thousands)
Assets:    
Money market funds$— $13,841 $— $13,841 
Insurance contracts*— 61,075 — 61,075 
Available-for-sale securities:
Mortgage-backed securities— 7,716 — 7,716 
U.S. Treasury securities— 3,944 — 3,944 
Total assets measured at fair value$— $86,576 $— $86,576 
* The insurance contracts invest approximately 58 percent in fixed-income investments, 17 percent in common stock of large-cap companies, 9 percent in target date investments, 7 percent in common stock of mid-cap companies, 4 percent in common stock of small-cap companies, 3 percent in cash equivalents, 1 percent in international investments, and 1 percent in real estate.
 Fair Value Measurements at December 31, 2025, Using 
Quoted Prices in
Active Markets
for Identical
Assets
 (Level 1)		Significant
Other
Observable
Inputs
(Level 2)		Significant
Unobservable
Inputs
 (Level 3)		Balance at December 31, 2025
(In thousands)
Assets:    
Money market funds$— $9,839 $— $9,839 
Insurance contracts*— 67,409 — 67,409 
Available-for-sale securities:
Mortgage-backed securities— 8,363 — 8,363 
U.S. Treasury securities— 4,025 — 4,025 
Total assets measured at fair value$— $89,636 $— $89,636 
* The insurance contracts invest approximately 57 percent in fixed-income investments, 18 percent in common stock of large-cap companies, 10 percent in target date investments, 7 percent in common stock of mid-cap companies, 4 percent in common stock of small-cap companies, 3 percent in cash equivalents, 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 was as follows:
 March 31, 2026March 31, 2025December 31, 2025
(In thousands)
Carrying amount$2,595,996 $2,193,676 $2,676,855 
Fair value$2,283,864 $1,902,217 $2,385,170 
v3.26.1
Debt (Tables)
 3 Months Ended
Mar. 31, 2026
Debt Disclosure [Abstract]  
Schedule of Line of Credit Facilities
The following table summarizes the outstanding revolving credit facilities of the Company and its subsidiaries:

Company
Debt-to-Total Capitalization Ratio at March 31, 2026
Provisions for Increased Borrowings, up to a maximum of:Facility
Limit		Amount Outstanding at March 31, 2026Amount Outstanding at March 31, 2025Amount Outstanding at December 31, 2025Letters of Credit at March 31, 2026Expiration
Date
(In millions)
Montana-Dakota Utilities Co.51 %$250.0 $200.0 $104.6 $51.1 $132.0 $— 12/11/30
Cascade Natural Gas Corporation50 %$225.0 $175.0 $124.3 $21.4 $96.5 $2.2 12/11/30
Intermountain Gas Company51 %$225.0 $175.0 $59.8 $83.5 $67.3 $— 12/11/30
MDU Resources Group, Inc.47 %$250.0 $200.0 $43.5 $— $32.9 $1.0 12/11/30
Schedule of Long-Term Debt Outstanding Long-term debt outstanding was as follows:
 
Weighted
Average
Interest
Rate at
March 31, 2026
March 31, 2026March 31, 2025December 31, 2025
 (In thousands)
Senior Notes due on dates ranging from July 15, 2026 to June 15, 2062
4.83 %$2,110,000 $1,947,000 $2,010,000 
Credit agreements due on December 11, 20305.47 %227,600 104,900 196,700 
Term Loan Agreements due on dates ranging from January 31, 2027 to April 1, 20394.04 %126,900 61,600 310,900 
Commercial paper supported by revolving credit agreement4.16 %104,617 51,100 132,000 
Medium-Term Notes due on dates ranging from September 15, 2027 to March 16, 2029
7.32 %35,000 35,000 35,000 
Other notes due on November 30, 2038
6.00 %324 342 329 
Less unamortized debt issuance costs8,445 6,266 8,074 
Total long-term debt2,595,996 2,193,676 2,676,855 
Less current maturities214,700 161,700 144,700 
Net long-term debt$2,381,296 $2,031,976 $2,532,155 
v3.26.1
Business segment data (Tables)
 3 Months Ended
Mar. 31, 2026
Segment Reporting [Abstract]  
Schedule of Segment Reporting Information, by Segment Information on the Company's segments was as follows:
Three Months Ended March 31, 2026ElectricNatural gas distributionPipelineOtherConsolidated
Three Months Ended March 31, 2025ElectricNatural gas distributionPipelineOtherConsolidated
Three Months Ended March 31, 2026ElectricNatural gas distributionPipelineOtherConsolidated
(In thousands)
Operating revenues:
External operating revenues$121,018 $462,347 $22,612 $— $605,977 
Intersegment operating revenues167 89 34,460 199 34,915 
Purchased natural gas sold:
External purchased natural gas sold— 239,391 — — 239,391 
Intersegment purchased natural gas sold— 34,420 — — 34,420 
Electric fuel and purchased power46,067 — — — 46,067 
Operation and maintenance:
External operation and maintenance28,705 65,126 20,769 305 114,905 
Intersegment operation and maintenance167 89 40 199 495 
Depreciation and amortization19,627 26,333 8,219 — 54,179 
Taxes, other than income5,520 26,452 3,758 — 35,730 
Other income:
External other income451 2,270 (423)307 2,605 
Intersegment other income— — 115 805 920 
Interest expense:
External interest expense11,911 16,286 3,102 1,386 32,685 
Intersegment interest expense— — 920 — 920 
Income tax (benefit) expense
(4,912)12,426 4,702 (7,538)4,678 
Income from continuing operations14,551 44,183 15,254 6,959 80,947 
Discontinued operations, net of tax— — — (130)(130)
Net income$14,551 $44,183 $15,254 $6,829 $80,817 
Three Months Ended March 31, 2025ElectricNatural gas distributionPipelineOtherConsolidated
(In thousands)
Operating revenues:
External operating revenues$112,261 $539,248 $23,323 $1 $674,833 
Intersegment operating revenues178 94 33,337 178 33,787 
Purchased natural gas sold:
External purchased natural gas sold— 317,157 — — 317,157 
Intersegment purchased natural gas sold— 33,323 — — 33,323 
Electric fuel and purchased power43,748 — — — 43,748 
Operation and maintenance:
External operation and maintenance28,407 63,484 19,239 (83)111,047 
Intersegment operation and maintenance178 94 14 178 464 
Depreciation and amortization17,183 26,122 7,956 — 51,261 
Taxes, other than income4,815 30,628 3,314 — 38,757 
Other income:
External other income992 3,301 307 397 4,997 
Intersegment other income— — 123 986 1,109 
Interest expense:
External interest expense7,887 14,876 3,121 938 26,822 
Intersegment interest expense— — 1,109 — 1,109 
Income tax (benefit) expense
(3,731)12,301 5,127 (5,126)8,571 
Income (loss) from continuing operations
14,944 44,658 17,210 5,655 82,467 
Discontinued operations, net of tax— — — (502)(502)
Net income$14,944 $44,658 $17,210 $5,153 $81,965 
Schedule of Reconciliation of Revenue from Segments to Consolidated
A reconciliation of reportable segment operating revenues to consolidated operating revenues is as follows:
Three Months Ended
March 31,
2026 2025 
(In thousands)
Operating revenues reconciliation:
Total reportable segment operating revenues$640,693 $708,441 
Other revenue199 179 
Elimination of intersegment operating revenues(34,915)(33,787)
Total consolidated operating revenues$605,977 $674,833 
v3.26.1
Employee benefit plans (Tables)
 3 Months Ended
Mar. 31, 2026
Retirement Benefits [Abstract]  
Schedule of Net Benefit Costs
Components of net periodic benefit cost for the Company's pension benefit plans were as follows:
Three Months Ended
March 31,
20262025
(In thousands)
Components of net periodic benefit cost:
Interest cost$3,128 $3,303 
Expected return on assets(3,391)(3,645)
Amortization of net actuarial loss1,432 1,193 
Net periodic benefit cost$1,169 $851 
Components of net periodic benefit credit for the Company's other postretirement benefit plans were as follows:
Three Months Ended
March 31,
20262025
(In thousands)
Components of net periodic benefit credit:
Service cost$94 $99 
Interest cost441 462 
Expected return on assets(1,270)(1,292)
Amortization of prior service credit(45)(290)
Amortization of net actuarial gain(23)(80)
Net periodic benefit credit, including amount capitalized(803)(1,101)
Less amount capitalized18 18 
Net periodic benefit credit$(821)$(1,119)
v3.26.1
Discontinued operations (Details) - Discontinued Operations, Disposed of by Means Other than Sale, Spinoff - Everus - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]    
Separation related costs $ 130 $ 502
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 $ 1,200 1,800
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   $ 13
v3.26.1
Receivables and allowance for expected credit losses - Schedule of Accounts Receivable, Allowance for Credit Loss (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Accounts Receivable, Allowance for Credit Loss [Roll Forward]    
Current expected credit loss provision $ 2,622 $ 3,152
Trade Accounts Receivable    
Accounts Receivable, Allowance for Credit Loss [Roll Forward]    
Beginning balance 1,949 1,839
Current expected credit loss provision 2,622 3,152
Less write-offs charged against the allowance 2,164 2,305
Credit loss recoveries collected 460 418
Ending balance 2,867 3,104
Electric | Trade Accounts Receivable    
Accounts Receivable, Allowance for Credit Loss [Roll Forward]    
Beginning balance 506 473
Current expected credit loss provision 952 939
Less write-offs charged against the allowance 1,066 1,036
Credit loss recoveries collected 188 166
Ending balance 580 542
Natural gas distribution | Trade Accounts Receivable    
Accounts Receivable, Allowance for Credit Loss [Roll Forward]    
Beginning balance 1,443 1,366
Current expected credit loss provision 1,670 2,213
Less write-offs charged against the allowance 1,098 1,269
Credit loss recoveries collected 272 252
Ending balance 2,287 2,562
Pipeline | Trade Accounts Receivable    
Accounts Receivable, Allowance for Credit Loss [Roll Forward]    
Beginning balance 0 0
Current expected credit loss provision 0 0
Less write-offs charged against the allowance 0 0
Credit loss recoveries collected 0 0
Ending balance $ 0 $ 0
v3.26.1
Inventories and natural gas in storage (Details) - USD ($)
$ in Thousands
Mar. 31, 2026
Dec. 31, 2025
Mar. 31, 2025
Inventory Disclosure [Abstract]      
Natural gas in storage (current) $ 14,796 $ 34,333 $ 13,579
Fuel stock 4,689 4,719 4,878
Total 19,485 39,052 18,457
Natural gas in storage noncurrent $ 47,800 $ 47,800 $ 48,500
v3.26.1
Earnings per share - Schedule of Weighted Average Common Shares Outstanding (Details) - $ / shares
shares in Thousands
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Earnings Per Share [Abstract]    
Weighted average common shares outstanding - basic (in shares) 205,438 204,142
Effect of dilutive performance share awards and restricted stock units (in shares) 1,556 817
Weighted average common shares outstanding - diluted (in shares) 206,994 204,959
Earnings per share - basic:    
Income from continuing operations (in usd per share) $ 0.39 $ 0.40
Discontinued operations, net of tax (in usd per share) 0 0
Earnings per share - basic (in usd per share) 0.39 0.40
Earnings per share - diluted:    
Income from continuing operations (in usd per share) 0.39 0.40
Discontinued operations, net of tax (in usd per share) 0 0
Earnings per share - diluted (in usd per share) $ 0.39 $ 0.40
Shares excluded from the calculation of diluted earnings per share (in shares) 50 0
Dividends declared per common share (in usd per share) $ 0.14 $ 0.13
v3.26.1
Equity (Details) - USD ($)
$ / shares in Units, $ in Millions
 1 Months Ended
Mar. 31, 2026
Dec. 23, 2025
Dec. 05, 2025
Aug. 07, 2025
Mar. 31, 2026
Class of Stock [Line Items]          
Price per share (in dollars per share)     $ 19.70    
Stock issued if FSAs were settled (in shares) 7,375,126        
Net settlement shares for counterparty if FSAs were settled 635,500        
At The Market Offering          
Class of Stock [Line Items]          
Sale of stock, aggregate offering price       $ 400.0  
Follow-On Public Stock Offering          
Class of Stock [Line Items]          
Sale of stock, number of shares issued (in shares)     10,152,284   4,300,000
Sale of stock, cash received         $ 81.3
Cash if FSAs were settled $ 139.6        
Net settlement amount for counterparty if FSAs were settled $ 13.2        
Over-Allotment Option          
Class of Stock [Line Items]          
Sale of stock, number of shares issued (in shares)   1,522,842      
v3.26.1
Revenue from contracts with customers - Schedule of Disaggregation of revenue (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Disaggregation of Revenue [Line Items]    
Revenues from contracts with customers $ 599,313 $ 678,020
Other revenues 6,664 (3,187)
Total external operating revenues 605,977 674,833
Total reportable segment operating revenues    
Disaggregation of Revenue [Line Items]    
Total external operating revenues 640,693 708,441
Intersegment eliminations    
Disaggregation of Revenue [Line Items]    
Revenues from contracts with customers (34,915) (33,787)
Total external operating revenues (34,915) (33,787)
Natural gas transportation    
Disaggregation of Revenue [Line Items]    
Revenues from contracts with customers 66,583 66,963
Natural gas storage    
Disaggregation of Revenue [Line Items]    
Revenues from contracts with customers 5,467 6,030
Other    
Disaggregation of Revenue [Line Items]    
Revenues from contracts with customers 45,517 42,610
Residential utility sales    
Disaggregation of Revenue [Line Items]    
Revenues from contracts with customers 285,727 328,920
Commercial utility sales    
Disaggregation of Revenue [Line Items]    
Revenues from contracts with customers 206,552 240,808
Industrial utility sales    
Disaggregation of Revenue [Line Items]    
Revenues from contracts with customers 22,422 24,626
Other utility sales    
Disaggregation of Revenue [Line Items]    
Revenues from contracts with customers 1,960 1,850
Electric | Total reportable segment operating revenues    
Disaggregation of Revenue [Line Items]    
Revenues from contracts with customers 122,652 116,589
Other revenues (1,634) (4,328)
Total external operating revenues 121,018 112,261
Electric | Intersegment eliminations    
Disaggregation of Revenue [Line Items]    
Revenues from contracts with customers (167) (178)
Total external operating revenues (167) (178)
Electric | Natural gas transportation | Total reportable segment operating revenues    
Disaggregation of Revenue [Line Items]    
Revenues from contracts with customers 0 0
Electric | Natural gas storage | Total reportable segment operating revenues    
Disaggregation of Revenue [Line Items]    
Revenues from contracts with customers 0 0
Electric | Other | Total reportable segment operating revenues    
Disaggregation of Revenue [Line Items]    
Revenues from contracts with customers 22,264 17,591
Electric | Residential utility sales | Total reportable segment operating revenues    
Disaggregation of Revenue [Line Items]    
Revenues from contracts with customers 39,401 39,685
Electric | Commercial utility sales | Total reportable segment operating revenues    
Disaggregation of Revenue [Line Items]    
Revenues from contracts with customers 49,184 48,477
Electric | Industrial utility sales | Total reportable segment operating revenues    
Disaggregation of Revenue [Line Items]    
Revenues from contracts with customers 10,010 9,164
Electric | Other utility sales | Total reportable segment operating revenues    
Disaggregation of Revenue [Line Items]    
Revenues from contracts with customers 1,960 1,850
Natural gas distribution | Total reportable segment operating revenues    
Disaggregation of Revenue [Line Items]    
Revenues from contracts with customers 454,073 538,122
Other revenues 8,274 1,126
Total external operating revenues 462,347 539,248
Natural gas distribution | Intersegment eliminations    
Disaggregation of Revenue [Line Items]    
Revenues from contracts with customers (89) (94)
Total external operating revenues (89) (94)
Natural gas distribution | Natural gas transportation | Total reportable segment operating revenues    
Disaggregation of Revenue [Line Items]    
Revenues from contracts with customers 17,506 17,710
Natural gas distribution | Natural gas storage | Total reportable segment operating revenues    
Disaggregation of Revenue [Line Items]    
Revenues from contracts with customers 0 0
Natural gas distribution | Other | Total reportable segment operating revenues    
Disaggregation of Revenue [Line Items]    
Revenues from contracts with customers 20,550 23,478
Natural gas distribution | Residential utility sales | Total reportable segment operating revenues    
Disaggregation of Revenue [Line Items]    
Revenues from contracts with customers 246,326 289,235
Natural gas distribution | Commercial utility sales | Total reportable segment operating revenues    
Disaggregation of Revenue [Line Items]    
Revenues from contracts with customers 157,368 192,331
Natural gas distribution | Industrial utility sales | Total reportable segment operating revenues    
Disaggregation of Revenue [Line Items]    
Revenues from contracts with customers 12,412 15,462
Natural gas distribution | Other utility sales | Total reportable segment operating revenues    
Disaggregation of Revenue [Line Items]    
Revenues from contracts with customers 0 0
Pipeline | Total reportable segment operating revenues    
Disaggregation of Revenue [Line Items]    
Revenues from contracts with customers 22,588 23,308
Other revenues 24 15
Total external operating revenues 22,612 23,323
Pipeline | Intersegment eliminations    
Disaggregation of Revenue [Line Items]    
Revenues from contracts with customers (34,460) (33,337)
Pipeline | Natural gas transportation | Total reportable segment operating revenues    
Disaggregation of Revenue [Line Items]    
Revenues from contracts with customers 49,077 49,253
Pipeline | Natural gas storage | Total reportable segment operating revenues    
Disaggregation of Revenue [Line Items]    
Revenues from contracts with customers 5,467 6,030
Pipeline | Other | Total reportable segment operating revenues    
Disaggregation of Revenue [Line Items]    
Revenues from contracts with customers 2,504 1,362
Pipeline | Residential utility sales | Total reportable segment operating revenues    
Disaggregation of Revenue [Line Items]    
Revenues from contracts with customers 0 0
Pipeline | Commercial utility sales | Total reportable segment operating revenues    
Disaggregation of Revenue [Line Items]    
Revenues from contracts with customers 0 0
Pipeline | Industrial utility sales | Total reportable segment operating revenues    
Disaggregation of Revenue [Line Items]    
Revenues from contracts with customers 0 0
Pipeline | Other utility sales | Total reportable segment operating revenues    
Disaggregation of Revenue [Line Items]    
Revenues from contracts with customers 0 0
Other | Total reportable segment operating revenues    
Disaggregation of Revenue [Line Items]    
Revenues from contracts with customers 0 1
Other revenues 0 0
Total external operating revenues 0 1
Other | Intersegment eliminations    
Disaggregation of Revenue [Line Items]    
Revenues from contracts with customers (199) (178)
Total external operating revenues (199) (178)
Other | Natural gas transportation | Total reportable segment operating revenues    
Disaggregation of Revenue [Line Items]    
Revenues from contracts with customers 0 0
Other | Natural gas storage | Total reportable segment operating revenues    
Disaggregation of Revenue [Line Items]    
Revenues from contracts with customers 0 0
Other | Other | Total reportable segment operating revenues    
Disaggregation of Revenue [Line Items]    
Revenues from contracts with customers 199 179
Other | Residential utility sales | Total reportable segment operating revenues    
Disaggregation of Revenue [Line Items]    
Revenues from contracts with customers 0 0
Other | Commercial utility sales | Total reportable segment operating revenues    
Disaggregation of Revenue [Line Items]    
Revenues from contracts with customers 0 0
Other | Industrial utility sales | Total reportable segment operating revenues    
Disaggregation of Revenue [Line Items]    
Revenues from contracts with customers 0 0
Other | Other utility sales | Total reportable segment operating revenues    
Disaggregation of Revenue [Line Items]    
Revenues from contracts with customers $ 0 $ 0
v3.26.1
Revenue from contracts with customers - Narrative (Details)
Mar. 31, 2026
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-04-01  
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]  
Revenue, remaining performance obligation, expected timing of satisfaction, period 12 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2027-04-01  
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]  
Revenue, remaining performance obligation, expected timing of satisfaction, period 12 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2028-04-01  
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]  
Revenue, remaining performance obligation, expected timing of satisfaction, period
Pipeline  
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]  
Contract with customer, term 12 months
Pipeline | Firm Transportation Contract  
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]  
Revenue from contract with customer, term of contract 4 years
Pipeline | Firm Storage Contract  
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]  
Revenue from contract with customer, term of contract 1 year
v3.26.1
Revenue from contracts with customers - Schedule of Remaining Performance Obligations (Details)
$ in Millions
Mar. 31, 2026
USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]  
Remaining performance obligation, amount $ 510.2
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-04-01  
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]  
Remaining performance obligation, amount 85.4
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2027-04-01  
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]  
Remaining performance obligation, amount 78.4
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2028-04-01  
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]  
Remaining performance obligation, amount $ 346.4
v3.26.1
Regulatory matters - Schedule of Unamortized Regulatory Assets and Liabilities (Details) - USD ($)
$ in Thousands
Mar. 31, 2026
Dec. 31, 2025
Mar. 31, 2025
Regulatory assets:      
Current regulatory assets $ 190,679 $ 179,579 $ 143,341
Regulatory assets 293,973 297,218 312,008
Total regulatory assets 484,652 476,797 455,349
Regulatory liabilities:      
Regulatory liabilities due within one year 148,409 148,584 140,165
Regulatory liabilities 474,957 472,329 463,879
Total regulatory liabilities 623,366 620,913 604,044
Net regulatory position $ (138,714) (144,116) (148,695)
Environmental compliance programs      
Regulatory liabilities:      
Estimated Recovery or Refund Period 1 year    
Regulatory liabilities due within one year $ 90,692 89,306 65,680
Natural gas costs refundable through rate adjustments      
Regulatory liabilities:      
Estimated Recovery or Refund Period 1 year    
Regulatory liabilities due within one year $ 35,288 47,130 46,744
Demand Charges      
Regulatory liabilities:      
Estimated Recovery or Refund Period 1 year    
Regulatory liabilities due within one year $ 9,684 0 10,000
Margin sharing      
Regulatory liabilities:      
Estimated Recovery or Refund Period 1 year    
Regulatory liabilities due within one year $ 3,895 3,946 3,562
Taxes recoverable from customers      
Regulatory liabilities:      
Estimated Recovery or Refund Period 1 year    
Regulatory liabilities due within one year $ 2,228 2,301 2,087
Regulatory liabilities $ 173,860 176,665 182,742
Conservation programs      
Regulatory liabilities:      
Estimated Recovery or Refund Period 1 year    
Regulatory liabilities due within one year $ 1,103 733 2,782
Provision for rate refund      
Regulatory liabilities:      
Estimated Recovery or Refund Period 1 year    
Regulatory liabilities due within one year $ 1,062 1,780 3,833
Other      
Regulatory liabilities:      
Regulatory liabilities due within one year 4,457 3,388 5,477
Regulatory liabilities 2,718 2,589 2,252
Plant removal and decommissioning costs      
Regulatory liabilities:      
Regulatory liabilities 227,100 224,313 221,349
Cost recovery mechanisms      
Regulatory liabilities:      
Regulatory liabilities 43,896 41,323 33,373
Accumulated deferred investment tax credit      
Regulatory liabilities:      
Regulatory liabilities 22,607 22,663 19,301
Pension and postretirement benefits      
Regulatory liabilities:      
Regulatory liabilities $ 4,776 4,776 4,862
Minimum | Other      
Regulatory liabilities:      
Estimated Recovery or Refund Period 1 year    
Maximum | Other      
Regulatory liabilities:      
Estimated Recovery or Refund Period 12 years    
Maximum | Cost recovery mechanisms      
Regulatory liabilities:      
Estimated Recovery or Refund Period 16 years    
Environmental compliance programs      
Regulatory assets:      
Estimated Recovery or Refund Period 1 year    
Current regulatory assets $ 92,143 78,784 56,441
Conservation programs      
Regulatory assets:      
Estimated Recovery or Refund Period 1 year    
Current regulatory assets $ 29,078 29,148 16,902
Natural gas costs recoverable through rate adjustments      
Regulatory assets:      
Estimated Recovery or Refund Period 1 year    
Current regulatory assets $ 23,899 22,897 51,321
Decoupling mechanisms      
Regulatory assets:      
Estimated Recovery or Refund Period 1 year    
Current regulatory assets $ 22,497 17,091 4,769
Cost recovery mechanisms      
Regulatory assets:      
Current regulatory assets 15,327 13,460 4,806
Regulatory assets $ 61,151 63,328 72,764
Cost recovery mechanisms | Minimum      
Regulatory assets:      
Estimated Recovery or Refund Period 1 year    
Cost recovery mechanisms | Maximum      
Regulatory assets:      
Estimated Recovery or Refund Period 23 years    
Electric fuel and purchased power deferral      
Regulatory assets:      
Estimated Recovery or Refund Period 1 year    
Current regulatory assets $ 3,163 6,902 7,109
Other      
Regulatory assets:      
Current regulatory assets 4,572 11,297 1,993
Regulatory assets $ 3,693 4,095 4,797
Other | Minimum      
Regulatory assets:      
Estimated Recovery or Refund Period 1 year    
Other | Maximum      
Regulatory assets:      
Estimated Recovery or Refund Period 13 years    
Pension and postretirement benefits      
Regulatory assets:      
Regulatory assets $ 135,222 135,222 142,065
Plant costs/asset retirement obligations      
Regulatory assets:      
Regulatory assets 48,002 48,352 46,920
Manufactured gas plant site remediation      
Regulatory assets:      
Regulatory assets 28,466 28,411 27,443
Taxes recoverable from customers      
Regulatory assets:      
Regulatory assets $ 12,145 12,250 12,228
Covid-19 deferred costs      
Regulatory assets:      
Estimated Recovery or Refund Period 2 years    
Regulatory assets $ 3,637 3,761 3,926
Long-term debt refinancing costs      
Regulatory assets:      
Estimated Recovery or Refund Period 37 years    
Regulatory assets $ 1,657 $ 1,799 $ 1,865
v3.26.1
Regulatory matters - Narrative (Details) - USD ($)
$ in Millions
Mar. 31, 2026
Dec. 31, 2025
Mar. 31, 2025
Regulatory Assets and Liabilities Disclosure [Abstract]      
Regulatory assets not earning a rate of return $ 175.7 $ 174.3 $ 179.3
v3.26.1
Regulatory matters - Schedule of Regulatory Proceedings (Details) - USD ($)
$ in Millions
Jun. 01, 2026
Apr. 01, 2026
Mar. 01, 2026
Nov. 25, 2025
Oct. 31, 2025
Sep. 30, 2025
Jun. 01, 2025
Mar. 05, 2025
Feb. 24, 2025
Montana | General Rate Cases Pending | Electric                  
Regulatory Assets                  
Annual Revenue Increase (%), pending           20.20%      
Annual Revenue Increase (in millions), pending           $ 14.1      
ROE, pending           10.80%      
Montana | General Rate Cases Finalized | Natural Gas Distribution | Subsequent Event                  
Regulatory Assets                  
Interim rate increase (%) pending   16.20%              
Public utilities, interim rate increase (decrease), amount   $ 10.4              
Oregon | General Rate Cases Pending | Natural Gas Distribution                  
Regulatory Assets                  
Annual Revenue Increase (%), pending       15.80%          
Annual Revenue Increase (in millions), pending       $ 16.4          
ROE, pending       10.40%          
Washington | General Rate Cases Finalized | Natural Gas Distribution                  
Regulatory Assets                  
Annual Revenue Increase (%), approved     2.60%         7.90%  
Annual Revenue Increase (in millions), approved     $ 10.8       $ (3.7) $ 29.8  
ROE, approved                 9.50%
Washington | General Rate Cases Finalized | Natural Gas Distribution | Forecast                  
Regulatory Assets                  
Annual Revenue Increase (in millions), approved $ (2.1)                
Wyoming | General Rate Cases Finalized | Electric | Subsequent Event                  
Regulatory Assets                  
Annual Revenue Increase (%), approved   18.60%              
Annual Revenue Increase (in millions), approved   $ 5.8              
ROE, approved   9.70%              
South Dakota | Electric                  
Regulatory Assets                  
Annual Revenue Increase (in millions), pending         $ 1.1        
v3.26.1
Fair value measurements - Narrative (Details)
$ in Thousands
 3 Months Ended
Mar. 31, 2026
USD ($)
Jun. 30, 2025
USD ($)
Mar. 31, 2025
USD ($)
Dec. 31, 2025
USD ($)
Fair Value Disclosures [Abstract]        
Investments used to satisfy nonqualified benefit plans obligations $ 65,700   $ 61,100 $ 67,400
Unrealized gains (losses) on investments, net of insurance proceeds 505   $ 470  
Investment withdrawal, cash amount $ 4,000 $ 5,000    
Investment withdrawal, percentage 1.25 1.25    
v3.26.1
Fair value measurements - Schedule of Available-for-Sale Securities (Details) - USD ($)
$ in Thousands
Mar. 31, 2026
Dec. 31, 2025
Mar. 31, 2025
Debt Securities, Available-for-sale [Abstract]      
Cost $ 12,061 $ 12,531 $ 11,866
Gross Unrealized Gains 41 61 94
Gross Unrealized Losses 227 204 300
Fair Value 11,875 12,388 11,660
Mortgage-backed securities      
Debt Securities, Available-for-sale [Abstract]      
Cost 8,382 8,539 7,997
Gross Unrealized Gains 9 28 18
Gross Unrealized Losses 224 204 299
Fair Value 8,167 8,363 7,716
U.S. Treasury securities      
Debt Securities, Available-for-sale [Abstract]      
Cost 3,679 3,992 3,869
Gross Unrealized Gains 32 33 76
Gross Unrealized Losses 3 0 1
Fair Value $ 3,708 $ 4,025 $ 3,944
v3.26.1
Fair value measurements - Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis (Details) - USD ($)
$ in Thousands
Mar. 31, 2026
Dec. 31, 2025
Mar. 31, 2025
Debt Securities, Available-for-sale [Line Items]      
Available-for-sale securities: $ 11,875 $ 12,388 $ 11,660
Total assets measured at fair value $ 86,636 $ 89,636 $ 86,576
Percentage in fixed-income and other investments 54.00% 57.00% 58.00%
Percentage investment in common stock of large-cap companies 19.00% 18.00% 17.00%
Percentage investment in target date investments 10.00% 10.00% 9.00%
Percentage investment in common stock of mid-cap companies 8.00% 7.00% 7.00%
Percentage investment in common stock of small-cap companies 4.00% 4.00% 4.00%
Percentage investment in cash and cash equivalents 3.00% 3.00% 3.00%
Percentage investment in international investments 1.00% 1.00% 1.00%
Percentage investment in real estate 1.00%   1.00%
Quoted Prices in Active Markets for Identical Assets (Level 1)      
Debt Securities, Available-for-sale [Line Items]      
Total assets measured at fair value $ 0 $ 0 $ 0
Significant Other Observable Inputs (Level 2)      
Debt Securities, Available-for-sale [Line Items]      
Total assets measured at fair value 86,636 89,636 86,576
Significant Unobservable Inputs (Level 3)      
Debt Securities, Available-for-sale [Line Items]      
Total assets measured at fair value 0 0 0
Mortgage-backed securities      
Debt Securities, Available-for-sale [Line Items]      
Available-for-sale securities: 8,167 8,363 7,716
Mortgage-backed securities | Quoted Prices in Active Markets for Identical Assets (Level 1)      
Debt Securities, Available-for-sale [Line Items]      
Available-for-sale securities: 0 0 0
Mortgage-backed securities | Significant Other Observable Inputs (Level 2)      
Debt Securities, Available-for-sale [Line Items]      
Available-for-sale securities: 8,167 8,363 7,716
Mortgage-backed securities | Significant Unobservable Inputs (Level 3)      
Debt Securities, Available-for-sale [Line Items]      
Available-for-sale securities: 0 0 0
U.S. Treasury securities      
Debt Securities, Available-for-sale [Line Items]      
Available-for-sale securities: 3,708 4,025 3,944
U.S. Treasury securities | Quoted Prices in Active Markets for Identical Assets (Level 1)      
Debt Securities, Available-for-sale [Line Items]      
Available-for-sale securities: 0 0 0
U.S. Treasury securities | Significant Other Observable Inputs (Level 2)      
Debt Securities, Available-for-sale [Line Items]      
Available-for-sale securities: 3,708 4,025 3,944
U.S. Treasury securities | Significant Unobservable Inputs (Level 3)      
Debt Securities, Available-for-sale [Line Items]      
Available-for-sale securities: 0 0 0
Money market funds      
Debt Securities, Available-for-sale [Line Items]      
Assets: 9,104 9,839 13,841
Money market funds | Quoted Prices in Active Markets for Identical Assets (Level 1)      
Debt Securities, Available-for-sale [Line Items]      
Assets: 0 0 0
Money market funds | Significant Other Observable Inputs (Level 2)      
Debt Securities, Available-for-sale [Line Items]      
Assets: 9,104 9,839 13,841
Money market funds | Significant Unobservable Inputs (Level 3)      
Debt Securities, Available-for-sale [Line Items]      
Assets: 0 0 0
Insurance contracts      
Debt Securities, Available-for-sale [Line Items]      
Assets: 65,657 67,409 61,075
Insurance contracts | Quoted Prices in Active Markets for Identical Assets (Level 1)      
Debt Securities, Available-for-sale [Line Items]      
Assets: 0 0 0
Insurance contracts | Significant Other Observable Inputs (Level 2)      
Debt Securities, Available-for-sale [Line Items]      
Assets: 65,657 67,409 61,075
Insurance contracts | Significant Unobservable Inputs (Level 3)      
Debt Securities, Available-for-sale [Line Items]      
Assets: $ 0 $ 0 $ 0
v3.26.1
Fair value measurements - Schedule of Fair Value of Long-Term Debt Outstanding (Details) - USD ($)
$ in Thousands
Mar. 31, 2026
Dec. 31, 2025
Mar. 31, 2025
Fair value, balance sheet grouping [Line Items]      
Long-term debt $ 2,595,996 $ 2,676,855 $ 2,193,676
Carrying amount      
Fair value, balance sheet grouping [Line Items]      
Long-term debt 2,595,996 2,676,855 2,193,676
Fair value      
Fair value, balance sheet grouping [Line Items]      
Long-term debt, fair value $ 2,283,864 $ 2,385,170 $ 1,902,217
v3.26.1
Debt - Narrative (Details) - USD ($)
$ in Thousands
 1 Months Ended 3 Months Ended
Feb. 02, 2026
Oct. 28, 2025
Mar. 31, 2026
Feb. 28, 2026
Mar. 31, 2026
Mar. 31, 2025
Jan. 15, 2026
Dec. 31, 2025
Dec. 30, 2025
Line of Credit Facility [Line Items]                  
Repayments of long-term debt         $ 218,937 $ 99,104      
Revolving Credit Facility | Montana-Dakota Utilities Co.                  
Line of Credit Facility [Line Items]                  
Ratio of total debt to total capitalization     6500.00%   6500.00%        
Senior Notes                  
Line of Credit Facility [Line Items]                  
Long-term debt, gross     $ 2,110,000   $ 2,110,000 $ 1,947,000   $ 2,010,000  
Senior Notes | Montana-Dakota Utilities Co.                  
Line of Credit Facility [Line Items]                  
Ratio of total debt to total capitalization   65.00%              
Debt instrument, face amount   $ 250,000              
Interest rate, stated percentage   5.96%              
Notes issued $ 100,000 $ 150,000              
Term Loan Agreement | Montana-Dakota Utilities Co.                  
Line of Credit Facility [Line Items]                  
Ratio of total debt to total capitalization                 65.00%
Debt instrument, face amount                 $ 250,000
Repayments of long-term debt     $ 80,000 $ 100,000          
Uncommitted Note Purchase And Private Shelf Agreement | WBI Energy Transmission                  
Line of Credit Facility [Line Items]                  
Facility Limit             $ 350,000    
Long-term debt, gross             235,000    
Line of credit facility, remaining borrowing capacity             $ 115,000    
Total debt to total capitalization     39.00%   39.00%        
v3.26.1
Debt - Schedule of Credit Facilities (Details) - USD ($)
Mar. 31, 2026
Dec. 31, 2025
Mar. 31, 2025
Line of Credit Facility [Line Items]      
Letters of credit at end of period $ 0    
Revolving Credit Facility | Montana-Dakota Utilities Co. | Credit Agreement Expiring October 2028      
Line of Credit Facility [Line Items]      
Debt-to-Total Capitalization Ratio at March 31, 2026 51.00%    
Provisions for Increased Borrowings, up to a maximum of: $ 250,000,000.0    
Facility Limit 200,000,000.0    
Amount outstanding, end of period 104,600,000 $ 132,000,000.0 $ 51,100,000
Letters of credit at end of period $ 0    
Revolving Credit Facility | Cascade Natural Gas Corporation | Credit Agreement Expiring June 2029      
Line of Credit Facility [Line Items]      
Debt-to-Total Capitalization Ratio at March 31, 2026 50.00%    
Provisions for Increased Borrowings, up to a maximum of: $ 225,000,000.0    
Facility Limit 175,000,000.0    
Amount outstanding, end of period 124,300,000 96,500,000 21,400,000
Letters of credit at end of period $ 2,200,000    
Revolving Credit Facility | Intermountain Gas Company | Credit Agreement Expiring June 2029      
Line of Credit Facility [Line Items]      
Debt-to-Total Capitalization Ratio at March 31, 2026 51.00%    
Provisions for Increased Borrowings, up to a maximum of: $ 225,000,000.0    
Facility Limit 175,000,000.0    
Amount outstanding, end of period 59,800,000 67,300,000 83,500,000
Letters of credit at end of period $ 0    
Revolving Credit Facility | MDU Resources Group, Inc. | Credit Agreement Expiring May 2028      
Line of Credit Facility [Line Items]      
Debt-to-Total Capitalization Ratio at March 31, 2026 47.00%    
Provisions for Increased Borrowings, up to a maximum of: $ 250,000,000.0    
Facility Limit 200,000,000.0    
Amount outstanding, end of period 43,500,000 $ 32,900,000 $ 0
Letters of credit at end of period $ 1,000,000.0    
v3.26.1
Debt - Schedule of Long-Term Debt Outstanding (Details) - USD ($)
$ in Thousands
Mar. 31, 2026
Dec. 31, 2025
Mar. 31, 2025
Long-term debt outstanding [Line Items]      
Less unamortized debt issuance costs $ 8,445 $ 8,074 $ 6,266
Total long-term debt 2,595,996 2,676,855 2,193,676
Less current maturities 214,700 144,700 161,700
Net long-term debt $ 2,381,296 2,532,155 2,031,976
Senior Notes      
Long-term debt outstanding [Line Items]      
Weighted average interest rate 4.83%    
Long-term debt, gross $ 2,110,000 2,010,000 1,947,000
Line of Credit      
Long-term debt outstanding [Line Items]      
Weighted average interest rate 5.47%    
Long-term debt, gross $ 227,600 196,700 104,900
Term Loan Agreements      
Long-term debt outstanding [Line Items]      
Weighted average interest rate 4.04%    
Long-term debt, gross $ 126,900 310,900 61,600
Commercial Paper      
Long-term debt outstanding [Line Items]      
Weighted average interest rate 4.16%    
Long-term debt, gross $ 104,617 132,000 51,100
Medium-Term Notes      
Long-term debt outstanding [Line Items]      
Weighted average interest rate 7.32%    
Long-term debt, gross $ 35,000 35,000 35,000
Other Notes      
Long-term debt outstanding [Line Items]      
Weighted average interest rate 6.00%    
Long-term debt, gross $ 324 $ 329 $ 342
v3.26.1
Business Segment Data - Schedule of Segment Reporting Information (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Segment Reporting [Abstract]    
Number Of Reportable Segments Not Disclosed Flag reportable segments  
Segment Reporting Information [Line Items]    
Operating revenues  $ 605,977 $ 674,833
Purchased natural gas sold 239,391 317,157
Electric fuel and purchased power 46,067 43,748
Operation and maintenance 114,905 111,047
Depreciation and amortization 54,179 51,261
Taxes, other than income 35,730 38,757
Other income 2,605 4,997
Interest expense 32,685 26,822
Income tax (benefit) expense 4,678 8,571
Income from continuing operations 80,947 82,467
Discontinued operations, net of tax (130) (502)
Net income 80,817 81,965
Total reportable segment operating revenues    
Segment Reporting Information [Line Items]    
Operating revenues  640,693 708,441
Total reportable segment operating revenues | Electric    
Segment Reporting Information [Line Items]    
Operating revenues  121,018 112,261
Purchased natural gas sold 0 0
Electric fuel and purchased power 46,067 43,748
Operation and maintenance 28,705 28,407
Depreciation and amortization 19,627 17,183
Taxes, other than income 5,520 4,815
Other income 451 992
Interest expense 11,911 7,887
Income tax (benefit) expense (4,912) (3,731)
Income from continuing operations 14,551 14,944
Discontinued operations, net of tax 0 0
Net income 14,551 14,944
Total reportable segment operating revenues | Natural gas distribution    
Segment Reporting Information [Line Items]    
Operating revenues  462,347 539,248
Purchased natural gas sold 239,391 317,157
Electric fuel and purchased power 0 0
Operation and maintenance 65,126 63,484
Depreciation and amortization 26,333 26,122
Taxes, other than income 26,452 30,628
Other income 2,270 3,301
Interest expense 16,286 14,876
Income tax (benefit) expense 12,426 12,301
Income from continuing operations 44,183 44,658
Discontinued operations, net of tax 0 0
Net income 44,183 44,658
Total reportable segment operating revenues | Pipeline    
Segment Reporting Information [Line Items]    
Operating revenues  22,612 23,323
Purchased natural gas sold 0 0
Electric fuel and purchased power 0 0
Operation and maintenance 20,769 19,239
Depreciation and amortization 8,219 7,956
Taxes, other than income 3,758 3,314
Other income (423) 307
Interest expense 3,102 3,121
Income tax (benefit) expense 4,702 5,127
Income from continuing operations 15,254 17,210
Discontinued operations, net of tax 0 0
Net income 15,254 17,210
Total reportable segment operating revenues | Other    
Segment Reporting Information [Line Items]    
Operating revenues  0 1
Purchased natural gas sold 0 0
Electric fuel and purchased power 0 0
Operation and maintenance 305 (83)
Depreciation and amortization 0 0
Taxes, other than income 0 0
Other income 307 397
Interest expense 1,386 938
Income tax (benefit) expense (7,538) (5,126)
Income from continuing operations 6,959 5,655
Discontinued operations, net of tax (130) (502)
Net income 6,829 5,153
Intersegment eliminations    
Segment Reporting Information [Line Items]    
Operating revenues  (34,915) (33,787)
Purchased natural gas sold (34,420) (33,323)
Operation and maintenance (495) (464)
Other income (920) (1,109)
Interest expense (920) (1,109)
Intersegment eliminations | Electric    
Segment Reporting Information [Line Items]    
Operating revenues  (167) (178)
Purchased natural gas sold 0 0
Operation and maintenance (167) (178)
Other income 0 0
Interest expense 0 0
Intersegment eliminations | Natural gas distribution    
Segment Reporting Information [Line Items]    
Operating revenues  (89) (94)
Purchased natural gas sold (34,420) (33,323)
Operation and maintenance (89) (94)
Other income 0 0
Interest expense 0 0
Intersegment eliminations | Pipeline    
Segment Reporting Information [Line Items]    
Operating revenues  (34,460) (33,337)
Purchased natural gas sold 0 0
Operation and maintenance (40) (14)
Other income (115) (123)
Interest expense (920) (1,109)
Intersegment eliminations | Other    
Segment Reporting Information [Line Items]    
Operating revenues  (199) (178)
Purchased natural gas sold 0 0
Operation and maintenance (199) (178)
Other income (805) (986)
Interest expense $ 0 $ 0
v3.26.1
Business segment data - Schedule of Operating Revenues Reconciliation (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Segment Reporting, Revenue Reconciling Item [Line Items]    
External operating revenues $ 605,977 $ 674,833
Total reportable segment operating revenues    
Segment Reporting, Revenue Reconciling Item [Line Items]    
External operating revenues 640,693 708,441
Other revenue    
Segment Reporting, Revenue Reconciling Item [Line Items]    
External operating revenues 199 179
Elimination of intersegment operating revenues    
Segment Reporting, Revenue Reconciling Item [Line Items]    
External operating revenues $ (34,915) $ (33,787)
v3.26.1
Employee benefit plans - Schedule of Components of Net Periodic Benefit Cost (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Pension benefits    
Defined benefit plan disclosure, net periodic benefit cost [Line Items]    
Interest cost $ 3,128 $ 3,303
Expected return on assets (3,391) (3,645)
Amortization of net actuarial gain 1,432 1,193
Net periodic benefit credit 1,169 851
Other postretirement benefits    
Defined benefit plan disclosure, net periodic benefit cost [Line Items]    
Service cost 94 99
Interest cost 441 462
Expected return on assets (1,270) (1,292)
Amortization of prior service credit (45) (290)
Amortization of net actuarial gain (23) (80)
Net periodic benefit credit, including amount capitalized (803) (1,101)
Less amount capitalized 18 18
Net periodic benefit credit $ (821) $ (1,119)
v3.26.1
Employee benefit plans - Narrative (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Supplemental employee retirement plans    
Defined benefit plan disclosure, net periodic benefit cost [Line Items]    
Net periodic benefit cost (credit) $ 662 $ 716
v3.26.1
Commitments and contingencies - Litigation (Details) - USD ($)
 1 Months Ended
Jan. 31, 2026
Mar. 31, 2026
Dec. 31, 2025
Mar. 31, 2025
Commitments and Contingencies Disclosure [Abstract]        
Potential liabilities related to litigation and environmental matters   $ 24,900,000 $ 26,100,000 $ 24,300,000
Loss contingency, receivable   83,000 1,600,000 541,000
Loss contingency, regulatory asset   $ 23,000,000.0 23,200,000 $ 22,700,000
Loss contingency, complaint $ 2,000,000.0      
Amount suspended $ 250,000      
Loss contingency accrued     $ 1,750,000  
v3.26.1
Commitments and contingencies - Guarantees (Details)
Mar. 31, 2026
USD ($)
Guarantor Obligations [Line Items]  
Outstanding letters of credit $ 0
Amount of surety bonds outstanding 13,400,000
Line of Credit  
Guarantor Obligations [Line Items]  
Line of credit facility, maximum borrowing capacity $ 3,200,000
v3.26.1
Commitments and contingencies - Leases (Details)
$ in Millions
Mar. 31, 2026
USD ($)
Commitments and Contingencies Disclosure [Abstract]  
Lease receivables $ 0.0
v3.26.1
Commitments and contingencies - Variable Interest Entities (Details)
$ in Millions
Mar. 31, 2026
USD ($)
Fuel contract  
Variable Interest Entities [Line Items]  
Variable interest entity, reporting entity involvement, maximum loss exposure, amount $ 23.0