OTTER TAIL CORP, 10-K filed on 2/14/2024
Annual Report
v3.24.0.1
Cover - USD ($)
 12 Months Ended
Dec. 31, 2023
Jan. 31, 2024
Jun. 30, 2023
Cover [Abstract]      
Document Type 10-K    
Document Annual Report true    
Document Period End Date Dec. 31, 2023    
Current Fiscal Year End Date --12-31    
Document Transition Report false    
Entity File Number 0-53713    
Entity Registrant Name OTTER TAIL CORPORATION    
Entity Incorporation, State or Country Code MN    
Entity Tax Identification Number 27-0383995    
Entity Address, Address Line One 215 South Cascade Street    
Entity Address, Address Line Two Box 496    
Entity Address, City or Town Fergus Falls    
Entity Address, State or Province MN    
Entity Address, Postal Zip Code 56538-0496    
City Area Code 866    
Local Phone Number 410-8780    
Title of 12(b) Security Common Shares, par value $5.00 per share    
Trading Symbol OTTR    
Security Exchange Name NASDAQ    
Entity Well-known Seasoned Issuer Yes    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Filer Category Large Accelerated Filer    
Entity Small Business false    
Entity Emerging Growth Company false    
ICFR Auditor Attestation Flag true    
Document Financial Statement Error Correction false    
Entity Shell Company false    
Entity Public Float     $ 3,646,181,401
Entity Common Stock, Shares Outstanding   41,710,521  
Documents Incorporated by Reference
The Registrant's definitive Proxy Statement for its 2024 Annual Meeting of Shareholders is incorporated by reference into Part III of this Form 10-K.
    
Entity Central Index Key 0001466593    
Amendment Flag false    
Document Fiscal Period Focus FY    
Document Fiscal Year Focus 2023    
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Audit Information
 12 Months Ended
Dec. 31, 2023
Auditor Information [Abstract]  
Auditor Firm ID 34
Auditor Name Deloitte & Touche LLP
Auditor Location Minneapolis, Minnesota
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CONSOLIDATED BALANCE SHEETS - USD ($)
$ in Thousands
Dec. 31, 2023
Dec. 31, 2022
Current Assets    
Cash and Cash Equivalents $ 230,373 $ 118,996
Receivables, net of allowance for credit losses 157,143 144,393
Inventories 149,701 145,952
Regulatory Assets 16,127 24,999
Other Current Assets 16,826 18,412
Total Current Assets 570,170 452,752
Noncurrent Assets    
Investments 62,516 54,845
Property, Plant and Equipment, net of accumulated depreciation 2,418,375 2,212,717
Regulatory Assets 95,715 94,655
Intangible Assets, net of accumulated amortization 6,843 7,943
Goodwill 37,572 37,572
Other Noncurrent Assets 51,377 41,177
Total Noncurrent Assets 2,672,398 2,448,909
Total Assets 3,242,568 2,901,661
Current Liabilities    
Short-Term Debt 81,422 8,204
Accounts Payable 94,428 104,400
Accrued Salaries and Wages 38,134 32,327
Accrued Taxes 26,590 19,340
Regulatory Liabilities 25,408 17,300
Other Current Liabilities 43,775 56,065
Total Current Liabilities 309,757 237,636
Noncurrent Liabilities and Deferred Credits    
Pension Benefit Liability 33,101 33,210
Other Postretirement Benefits Liability 27,676 46,977
Regulatory Liabilities 276,547 244,497
Deferred Income Taxes 237,273 221,302
Deferred Tax Credits 15,172 15,916
Other Noncurrent Liabilities 75,977 60,985
Total Noncurrent Liabilities and Deferred Credits 665,746 622,887
Commitments and Contingencies (Note 13)
Capitalization    
Long-Term Debt 824,059 823,821
Shareholders' Equity    
Common Stock: 50,000,000 shares authorized of $5 par value; 41,710,521 and 41,631,113 outstanding at December 31, 2023 and 2022 208,553 208,156
Additional Paid-In Capital 426,963 423,034
Retained Earnings 806,342 585,212
Accumulated Other Comprehensive Income 1,148 915
Total Shareholders' Equity 1,443,006 1,217,317
Total Capitalization 2,267,065 2,041,138
Total Liabilities and Shareholders' Equity $ 3,242,568 $ 2,901,661
v3.24.0.1
CONSOLIDATED BALANCE SHEETS (Parentheticals) - $ / shares
Dec. 31, 2023
Dec. 31, 2022
Statement of Financial Position [Abstract]    
Common stock, shares authorized (in shares) 50,000,000 50,000,000
Common stock, par value (in dollars per share) $ 5 $ 5
Common stock, shares outstanding (in shares) 41,710,521 41,631,113
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CONSOLIDATED STATEMENTS OF INCOME - USD ($)
shares in Thousands, $ in Thousands
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Operating Revenues      
Total Operating Revenues $ 1,349,166 $ 1,460,209 $ 1,196,844
Operating Expenses      
Electric Production Fuel 60,339 65,110 59,327
Electric Purchased Power 78,292 100,281 65,409
Electric Operating and Maintenance Expenses 191,263 181,378 159,669
Cost of Products Sold (excluding depreciation) 454,122 542,944 488,370
Nonelectric Selling, General, and Administrative Expenses 72,663 69,718 65,394
Depreciation and Amortization 97,954 92,597 91,358
Electric Property Taxes 16,614 17,742 17,609
Total Operating Expenses 971,247 1,069,770 947,136
Operating Income 377,919 390,439 249,708
Other Income and Expense      
Interest Expense (37,677) (36,016) (37,771)
Nonservice Cost Components of Postretirement Benefits 10,597 1,075 (2,016)
Other Income (Expense), net 12,650 2,037 2,900
Income Before Income Taxes 363,489 357,535 212,821
Income Tax Expense 69,298 73,351 36,052
Net Income $ 294,191 $ 284,184 $ 176,769
Weighted-Average Common Shares Outstanding:      
Basic (in shares) 41,668 41,586 41,491
Diluted (in shares) 42,039 41,931 41,818
Earnings Per Share:      
Basic (in dollars per share) $ 7.06 $ 6.83 $ 4.26
Diluted (in dollars per share) $ 7.00 $ 6.78 $ 4.23
Electric      
Operating Revenues      
Total Operating Revenues $ 528,359 $ 549,699 $ 480,321
Product Sales      
Operating Revenues      
Total Operating Revenues $ 820,807 $ 910,510 $ 716,523
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CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Statement of Comprehensive Income [Abstract]      
Net Income $ 294,191 $ 284,184 $ 176,769
Other Comprehensive Income (Loss):      
Unrealized Gain (Loss) on Available-for-Sale Securities, net of tax (expense) benefit of $(51), $115 and $52 192 (432) (196)
Pension and Other Postretirement Benefit Plan, net of tax expense of $14, $2,769 and $766 41 7,871 2,179
Total Other Comprehensive Income 233 7,439 1,983
Total Comprehensive Income $ 294,424 $ 291,623 $ 178,752
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CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Parentheticals) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Statement of Comprehensive Income [Abstract]      
Unrealized Gain (Loss) on Available-for-Sale Securities, tax (expense) benefit $ (51) $ 115 $ 52
Pension and Other Postretirement Benefit Plan, tax expense $ (14) $ (2,769) $ (766)
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CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($)
$ in Thousands
Total
Common Shares
Additional Paid-In Capital
Retained Earnings
Accumulated Other Comprehensive Income (Loss)
Beginning balance (in shares) at Dec. 31, 2020   41,469,879      
Beginning balance at Dec. 31, 2020 $ 870,966 $ 207,349 $ 414,246 $ 257,878 $ (8,507)
Increase (Decrease) in Stockholders' Equity [Roll Forward]          
Stock Issued Under Dividend Reinvestment and Stock Purchase Plans, Net of Expenses (in shares)   11,540      
Stock Issued Under Dividend Reinvestment and Stock Purchase Plans, Net of Expenses 504 $ 58 446    
Stock Issued Under Share-Based Compensation Plans, Net of Shares Withheld for Employee Taxes (in shares)   70,105      
Stock Issued Under Share-Based Compensation Plans, Net of Shares Withheld for Employee Taxes (1,489) $ 351 (1,840)    
Net Income 176,769     176,769  
Other Comprehensive Income 1,983       1,983
Stock Compensation Expense 6,908   6,908    
Common Dividends (64,864)     (64,864)  
Ending balance (in shares) at Dec. 31, 2021   41,551,524      
Ending balance at Dec. 31, 2021 990,777 $ 207,758 419,760 369,783 (6,524)
Increase (Decrease) in Stockholders' Equity [Roll Forward]          
Employee Stock Purchase Plan Expenses (219)   (219)    
Stock Issued Under Share-Based Compensation Plans, Net of Shares Withheld for Employee Taxes (in shares)   79,589      
Stock Issued Under Share-Based Compensation Plans, Net of Shares Withheld for Employee Taxes (2,923) $ 398 (3,321)    
Net Income 284,184     284,184  
Other Comprehensive Income 7,439       7,439
Stock Compensation Expense 6,814   6,814    
Common Dividends $ (68,755)     (68,755)  
Ending balance (in shares) at Dec. 31, 2022 41,631,113 41,631,113      
Ending balance at Dec. 31, 2022 $ 1,217,317 $ 208,156 423,034 585,212 915
Increase (Decrease) in Stockholders' Equity [Roll Forward]          
Employee Stock Purchase Plan Expenses (339)   (339)    
Stock Issued Under Share-Based Compensation Plans, Net of Shares Withheld for Employee Taxes (in shares)   79,408      
Stock Issued Under Share-Based Compensation Plans, Net of Shares Withheld for Employee Taxes (3,088) $ 397 (3,485)    
Net Income 294,191     294,191  
Other Comprehensive Income 233       233
Stock Compensation Expense 7,753   7,753    
Common Dividends $ (73,061)     (73,061)  
Ending balance (in shares) at Dec. 31, 2023 41,710,521 41,710,521      
Ending balance at Dec. 31, 2023 $ 1,443,006 $ 208,553 $ 426,963 $ 806,342 $ 1,148
v3.24.0.1
CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY (Parentheticals) - $ / shares
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Statement of Stockholders' Equity [Abstract]      
Common Dividends (in dollars per share) $ 1.75 $ 1.65 $ 1.56
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CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Operating Activities      
Net Income $ 294,191 $ 284,184 $ 176,769
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities:      
Depreciation and Amortization 97,954 92,597 91,358
Deferred Tax Credits (744) (745) (744)
Deferred Income Taxes 13,508 32,424 28,896
Discretionary Contribution to Pension Plan 0 (20,000) (10,000)
Investment (Gains) Losses (7,222) 3,296 (4,524)
Stock Compensation Expense 7,753 6,814 6,908
Other, net (423) (1,473) 667
Changes in Operating Assets and Liabilities:      
Receivables (12,750) 30,560 (60,994)
Inventories (2,450) 5,339 (54,313)
Regulatory Assets 12,479 (2,464) (4,803)
Other Assets 2,817 (368) (14,146)
Accounts Payable (9,988) (29,763) 38,734
Accrued and Other Liabilities 6 (5,490) 28,386
Regulatory Liabilities 20,973 (6,846) 1,948
Pension and Other Postretirement Benefits (11,605) 1,244 7,101
Net Cash Provided by Operating Activities 404,499 389,309 231,243
Investing Activities      
Capital Expenditures (287,134) (171,134) (171,829)
Proceeds from Disposal of Noncurrent Assets 6,225 4,346 9,702
Purchases of Investments and Other Assets (8,378) (8,283) (9,383)
Net Cash Used in Investing Activities (289,287) (175,071) (171,510)
Financing Activities      
Net Borrowings (Repayments) on Short-Term Debt 73,218 (82,959) 10,166
Proceeds from Issuance of Common Stock 0 0 696
Proceeds from Issuance of Long-Term Debt 0 90,000 140,000
Payments for Retirement of Long-Term Debt 0 (30,000) (140,169)
Dividends Paid (73,061) (68,755) (64,864)
Payments for Shares Withheld for Employee Tax Obligations (3,088) (2,942) (1,507)
Other, net (904) (2,123) (3,681)
Net Cash Used in Financing Activities (3,835) (96,779) (59,359)
Net Change in Cash and Cash Equivalents 111,377 117,459 374
Cash and Cash Equivalents at Beginning of Period 118,996 1,537 1,163
Cash and Cash Equivalents at End of Period 230,373 118,996 1,537
Supplemental Disclosures of Cash Flow Information      
Interest, net of amount capitalized 36,956 35,699 36,881
Income Taxes 46,284 43,411 8,445
Supplemental Disclosure of Noncash Investing Activities      
Accrued Property, Plant and Equipment Additions $ 13,001 $ 12,420 $ 12,081
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Summary of Significant Accounting Policies
 12 Months Ended
Dec. 31, 2023
Accounting Policies [Abstract]  
Summary of Significant Accounting Policies Summary of Significant Accounting Policies
Overview
Otter Tail Corporation (OTC) and its subsidiaries (collectively, the "Company", "us", "our" or "we") form a diverse, multi-platform business consisting of a vertically integrated, regulated utility with generation, transmission and distribution facilities complemented by manufacturing businesses providing metal fabrication for custom machine parts and metal components, manufacturing of extruded and thermoformed plastic products, and manufacturing of PVC pipe products. We classify our business into three segments: Electric, Manufacturing and Plastics. Note 2 includes an additional description of the segments and financial information regarding each segment.
Principles of Consolidation
These consolidated financial statements are presented in accordance with U.S. generally accepted accounting principles and include the accounts of OTC and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation except, as applicable, profits on sales to our regulated electric utility company from our nonregulated businesses, which is in accordance with the accounting requirements of regulated operations.
Use of Estimates
We use estimates based on the best information available in recording transactions and balances resulting from business operations. As better information becomes available, or actual amounts are known, the recorded estimates are revised. Consequently, operating results can be affected by revisions to prior accounting estimates.
Reclassifications
Certain reclassifications of amounts previously reported have been made to the accompanying consolidated statements of cash flows to maintain consistency and comparability between periods presented. Other, net operating cash flows previously reported for the years ended December 31, 2022 and 2021, included $3.3 million of investment losses and $4.5 million of investment gains, respectively, which are presented separately in the current year, and excluded $1.7 million and $0.8 million of allowance for equity funds used during construction (AFUDC), which were previously presented separately. The reclassifications had no impact on previously reported net cash provided by operating activities, net cash used in investing activities, net cash used in financing activities, or cash and cash equivalents. Certain prior period amounts related to deferred tax assets and deferred tax liabilities included in footnote 12 have been reclassified to conform to the current year presentation.
Regulatory Accounting
Our regulated electric utility company, Otter Tail Power Company (OTP), is subject to regulation of rates and other matters by state utility commissions in Minnesota, North Dakota and South Dakota and by the FERC for certain interstate operations. OTP accounts for the financial effects of regulation in accordance with accounting guidance for regulated operations. This guidance allows for the recording of a regulatory asset for certain costs which otherwise would be recognized in the statement of income or comprehensive income based on an expectation that the cost will be recovered in future rates. This guidance also requires the recording of a regulatory liability for certain credits which would otherwise be recognized in the statement of income or comprehensive income based on an expectation that the amount will be returned to customers in future rates. Amounts recorded as regulatory assets and regulatory liabilities are generally recognized in the statements of income at the time they are reflected in customer rates. In the event OTP ceases to meet the criteria to apply the guidance for regulated operations, the regulatory assets and liabilities that no longer meet such criteria would be removed from the consolidated balance sheets and included in the consolidated statement of income as an expense or income item, or in the consolidated statement of comprehensive income as a loss or gain item, in the period in which the application of this guidance ceases.
Cash Equivalents
We consider all highly liquid investments purchased with maturity dates of 90 days or less to be cash equivalents.
Concentration of Deposits
We hold deposits with financial institutions which potentially subject us to a concentration risk. These deposits are guaranteed by the Federal Deposit Insurance Corporation up to an insurance limit of $250,000. Currently, our cash deposits exceed federally insured levels.
Revenue from Contracts with Customers
Due to our diverse business operations, the recognition of revenue from contracts with customers depends on the product produced and sold or service performed. We recognize revenue from contracts with customers at prices that are fixed or determinable as evidenced by an agreement with the customer, when we have met our performance obligation under the contract and it is probable that we will collect the amount to which we are entitled in exchange for the goods or services transferred or to be transferred to the customer. Depending on the product produced and sold or service performed and the terms of the agreement with the customer, we recognize revenue either over time, in the case of delivery or transmission of electricity or related services or the production and storage of certain custom-made products, or at a point in time for the delivery of standardized products and other products made to customer specifications where the terms of the contract require transfer of the completed product. Provisions for sales returns, early payment discounts, and volume-based variable pricing incentives are recorded as reductions to revenue at the time revenue is recognized based on customer history, historical information and current trends. We include revenues received for shipping and handling in operating revenues. Expenses paid for shipping and handling are recorded as part of cost of products sold. Sales or other taxes collected from customers are excluded from operating revenues.
Electric Segment Revenues. Most Electric segment revenues are earned from the generation, transmission and sale of electricity to retail customers at rates approved by state regulatory commissions. OTP also earns revenue from the transmission of electricity for others over the transmission assets it owns separately, or jointly with other transmission service providers, under rate tariffs established by the independent transmission system operator and approved by the FERC. A third source of revenue for OTP comes from the generation and sale of electricity to wholesale customers at contract or market rates. Revenues from all these sources meet the criteria to be classified as revenue from contracts with customers and are recognized over time as energy is delivered or transmitted. Revenue is recognized based on the metered quantity of electricity delivered or transmitted at the applicable rates. For electricity delivered and consumed after a meter is read but prior to the end of the reporting period, OTP records revenue and an unbilled receivable based on estimates of the amount of energy delivered to the customer.
Manufacturing Segment Revenues. Our Manufacturing segment businesses earn revenue predominantly from the production and delivery of custom-made or standardized parts and products to customers across several industries and from the production and sale of tools and dies to other manufacturers. For the production and delivery of standardized products and other products made to customer specifications where the terms of the contract require transfer of the completed product, we have met our performance obligation and recognize revenue at the point in time when the product is shipped. At this point we have no further obligation to provide services related to such products. The shipping terms used in these transactions are free on board (FOB) shipping point.
Plastics Segment Revenues. Our Plastics segment businesses earn revenue predominantly from the sale and delivery of standardized PVC pipe products produced at their manufacturing facilities. Revenue from the sale of these products is recognized at the point in time when the product is shipped as there is no further obligation to provide services related to such products and the shipping terms are FOB shipping point. We have one customer within our Plastics segment for which we produce and store a product made to the customer’s specifications and design under a build and hold agreement. For sales to this customer, we recognize revenue as the custom-made product is produced, adjusting the amount of revenue for volume rebate variable pricing considerations we expect the customer will earn and applicable early payment discounts we expect the customer will take. Ownership of the pipe transfers to the customer prior to delivery and we are paid a negotiated fee for storage of the pipe. Revenue for storage of the pipe is recognized over time as the pipe is stored.
Alternative Revenue
In addition to recognizing revenue from contracts with customers, our Electric segment business also records revenue under alternative revenue program (ARP) requirements. Certain rate rider mechanisms qualify as ARP revenues as they provide for adjustments to rates outside of a general rate case proceeding to encourage or incentivize investments in certain areas such as conservation, renewable energy, pollution reduction or control, improved infrastructure of the transmission grid or other programs that provide benefits to the general public under public policy, laws or regulations. ARP riders generally provide for the recovery of specified costs and investments and include an incentive component to provide the regulated utility with a return on amounts invested.
We accrue ARP revenue on the basis of cost incurred, investments made and returns on those investments that qualify for recovery through established riders. ARP revenue is disclosed separately from revenue from contracts with customers and we have elected to report ARP revenue on a net basis, whereby amounts initially recorded as ARP revenue in a period are presented net of the reversal of amounts previously recognized as ARP revenue that are reclassified and recorded as revenue from contracts with customers when such amounts are included in the price of electricity to customers.
Receivables and Allowance for Credit Losses
We grant credit to our customers in the normal course of business with repayment terms generally ranging from 30 to 90 days after the invoice date. Late fees are assessed on certain receivables once they are 30 days past due. Unbilled receivables represent estimates of energy delivered to customers but not yet billed.
Receivables are stated at the billed or estimated unbilled amount less an allowance for estimated credit losses. An allowance for credit losses is established based on losses expected to occur over the contractual life of the receivable. We estimate an allowance for credit losses on our trade and unbilled receivables by evaluating historical aging and write-off history, adjusted for current and forecasted economic conditions, for groups of receivables that share similar economic characteristics. Other receivables are evaluated by reviewing individual accounts, considering aging, financial condition of the debtor, recent payment history and other relevant factors. Account balances are written-off in the period they are deemed to be uncollectible.
Inventories
Inventories are valued at the lower of cost or net realizable value. Costs for fuel, material and supply inventories of our Electric segment are determined on an average cost basis. Costs for raw material, work in process and finished goods inventories of our Manufacturing and Plastics segments are determined on a first-in first-out (FIFO) basis.
Inventories consist of the following as of December 31, 2023 and 2022:
(in thousands)20232022
Finished Goods$47,614 $43,812 
Work in Process26,354 31,766 
Raw Material, Fuel and Supplies75,733 70,374 
Total Inventories$149,701 $145,952 
Investments
We invest in and hold, through rabbi trusts, corporate-owned life insurance policies to provide future funding for obligations under our supplemental pension plan and a nonqualified deferred compensation plan. The polices are recorded at cash surrender value and there are no restrictions on our ability to surrender the policies.
We hold debt, mutual fund, and money market fund investments either as investments within our captive insurance entity or to provide future funding for obligations under nonqualified deferred compensation plans. These investments are recorded at fair value. Debt securities are deemed to be available-for-sale securities, accordingly unrealized gains and losses are generally excluded from earnings and recognized in accumulated other comprehensive income. We evaluate whether declines in fair value of debt securities below the cost basis are other-than-temporary. Declines in fair value deemed to be other-than-temporary result in the recognition of unrealized losses, or a portion thereof, in earnings. Unrealized gains and losses on mutual and money market funds are recognized in earnings immediately.
The following is a summary of our investments at December 31, 2023 and 2022:
(in thousands)20232022
Corporate-Owned Life Insurance Policies$42,287 $38,991 
Corporate and Government Debt Securities
9,303 8,761 
Mutual Funds7,771 5,503 
Money Market Funds3,125 1,560 
Other Investments30 30 
Total Investments$62,516 $54,845 
The amount of unrealized gains and losses on debt securities as of December 31, 2023 and 2022 is not material and no unrealized losses were deemed to be other-than-temporary. In addition, the amount of unrealized gains and losses on marketable equity securities still held as of December 31, 2023 and 2022 is not material.
Property, Plant and Equipment
Electric plant is stated at original cost. The cost of additions includes contracted work, direct labor and materials, allocable overheads and AFUDC. The amount of interest capitalized to electric plant was $1.9 million in 2023, $0.9 million in 2022 and $0.6 million in 2021. The cost of depreciable units of property retired less salvage is charged to accumulated depreciation. Amounts recovered in rates for future removal costs are recorded as regulatory liabilities. Removal costs, when incurred, are charged against the regulatory liability. Maintenance, repairs and replacement of minor items are charged to operating expenses as incurred. The provisions for utility depreciation for financial reporting purposes are made on the straight-line method based on the estimated remaining service lives of the properties. Gains or losses on group asset dispositions are recorded to accumulated depreciation and impact current and future depreciation rates.
Property, plant and equipment of nonelectric operations are carried at historical cost and are depreciated on a straight-line basis over the assets’ estimated useful lives. The cost of additions includes contracted work, direct labor and materials, allocable overheads and capitalized interest. No interest was capitalized in 2023, 2022 or 2021. Maintenance and repairs are expensed as incurred. Gains or losses on asset dispositions are included in the determination of operating income.
The estimated service lives for rate-regulated electric assets and nonelectric assets are included below:
 Service Life Range
(years)LowHigh
Electric Assets:  
Production Plant21114
Transmission Plant5175
Distribution Plant1070
General Plant556
Nonelectric Assets:
Equipment220
Buildings and Leasehold Improvements240
Jointly Owned Facilities
OTP is a joint owner in two coal-fired steam-powered electric generation plants: Big Stone Plant near Big Stone City, South Dakota and Coyote Station near Beulah, North Dakota. OTP is also a joint owner, with other regional utilities, in five major transmission lines. OTP's interest in each jointly owned facility is reflected in the consolidated balance sheets on a pro-rata basis and OTP's share of direct revenue and expenses are included in operating revenues and expenses in the consolidated statements of income. Each participant in the jointly owned facilities finances their own investments.
Goodwill and Other Intangible Assets
Goodwill is recognized and initially measured as any excess of the acquisition-date consideration transferred in a business combination over amounts recognized for the net identifiable assets acquired. Goodwill is not amortized, but is tested for impairment annually, or more frequently if
an event occurs or circumstances change that would more likely than not result in an impairment of goodwill. Impairment testing is performed at the reporting unit level, which is defined as an operating segment or one level below an operating segment. We perform our impairment testing in the fourth quarter of each year and have identified three reporting units that carry a goodwill balance.
Our impairment testing includes both an optional qualitative assessment and the quantitative impairment assessment. Our qualitative assessment includes an analysis of relevant events and circumstances to determine if it is more likely than not that the fair value of the reporting unit exceeds its book value. If, after this assessment, we determine that it is not more likely than not that the fair value of a reporting unit is less than its carrying amount, no additional analysis is necessary. In contrast, if after the assessment we determine it is more likely than not that the fair value of a reporting unit is less than its carrying amount, or if we elect to skip the optional qualitative assessment, the quantitative impairment assessment is performed. The quantitative assessment is a single-step test that identifies both the existence of impairment and the amount of impairment loss by comparing the estimated fair value of a reporting unit to its carrying value, with any excess carrying value over the fair value being recognized as an impairment loss.
Intangible assets with finite lives, which primarily consist of customer relationships, are carried at estimated fair value at the time of acquisition less accumulated amortization. The costs of the intangible assets are amortized over their estimated useful lives, which generally range from 15 to 20 years.
Cloud Computing Costs
We capitalize implementation costs incurred in cloud computing arrangements that are service contracts consistent with capitalized implementation costs incurred to develop or obtain internal-use software. Costs are amortized on a straight-line basis over the life of the associated contract. Capitalized implementation costs are amortized over periods up to ten years. Capitalized costs and related accumulated amortization are included in other noncurrent assets on the consolidated balance sheets. Below are the amounts of capitalized cost and related accumulated amortization as of December 31, 2023 and 2022:
(in thousands)20232022
Cloud Computing Costs
$12,782 $9,024 
Accumulated Amortization
$(1,505)$(897)
Cloud Computing Costs, net
$11,277 $8,127 
Amortization expense of capitalized implementation costs for each of the years ended December 31, 2023, 2022 and 2021 totaled $1.3 million, $1.4 million, and $0.5 million.
Leases
We recognize right-of-use lease assets and a corresponding lease liability at the lease commencement date. The length of our lease agreements varies from less than one year to approximately ten years. We have elected to not record lease assets and liabilities for leases with a lease term at commencement of 12 months or less; such leases are expensed on a straight-line basis over the lease term. If a lease contains an option to extend the lease term and there is reasonable certainty the option will be exercised, the option is considered in the lease term at inception. We have elected to not separate non-lease components (e.g., common area maintenance) from lease components on real estate leases, accordingly the recognized lease asset and lease liability incorporate in their measurement payments for non-lease components. Certain leases include variable lease payments as the amounts are subject to change over the lease term. We are unable to determine the interest rate implicit in our leases thus we apply our incremental borrowing rate to capitalize the right-of-use asset and lease liability. We estimate our incremental borrowing rate by incorporating considerations of lease term and lessee entity.
Recoverability of Long-Lived Assets
We review our long-lived assets including, among other assets, property, plant and equipment, amortizing intangible assets and right-of-use lease assets, whenever events or changes in circumstances indicate the carrying amount of the assets may not be recoverable. We determine potential impairment by comparing the carrying amount of the assets with the net cash flows expected to be provided by operating activities of the business or related assets. If the sum of the expected future net cash flows is less than the carrying amount of the assets, an impairment loss would be recognized. Such an impairment loss would be measured as the amount by which the carrying amount exceeds the fair value of the asset.
Asset Retirement Obligations
Legal obligations related to the future retirement of long-lived assets are recognized as asset retirement obligations (ARO). An ARO is recognized in the period in which the legal obligation is incurred and the amount of the obligation can be reasonably estimated, with an offsetting increase to the associated long-lived asset. AROs are initially recognized at fair value and increased with the passage of time (accretion). ARO estimates are revised periodically with any adjustment reflected in the ARO and associated long-lived asset.
Income Taxes
We use the asset and liability method to account for income taxes. Under this method, deferred tax assets and liabilities are recognized for the expected future tax consequences of all temporary differences between the carrying amounts of assets and liabilities and their respective tax bases. Deferred taxes are recorded using the tax rates scheduled by tax law to be in effect in the periods when the temporary differences reverse. Deferred tax assets are reduced by a valuation allowance when it is more likely than not that a portion or all of the deferred tax assets will not be realized. The realizability of deferred tax assets is determined by taking into consideration forecasts of future taxable income, the reversal of other existing temporary differences, available net operating loss carryforwards and available tax planning strategies. Changes in valuation allowances are included in the provision for income taxes in the period of the changes.
We recognize the tax effects of all tax positions that are more-likely-than-not to be sustained on audit based solely on the technical merits of those positions as of the balance sheet date. Changes in the recognition or measurement of such positions are recognized in the provision for income taxes in the period of the changes. We classify interest and penalties on tax uncertainties as components of the provision for income taxes.
We have elected to account for transferable tax credits as a component of our income tax provision. We recognize the benefit of PTCs as a reduction of income tax expense in the period the credit is generated, which corresponds to the period the energy production occurs. We apply the deferral method of accounting for ITCs and state wind energy credits. Under this method, ITCs and state wind energy credits are amortized as a reduction to income tax expense over the estimated useful lives of the underlying property that gave rise to the credit.
Deferred Compensation Plans
The Company sponsors two nonqualified deferred compensation plans for the benefit of executive officers and other select employees. Each plan allows participants to defer a specified amount or percentage of base wages or incentive compensation into the plan, subject to certain limitations. The Company, at its discretion, may make employer contributions to either plan during any annual period. Participant and employer deferred amounts are segregated into one or more accounts chosen by the participant. Participants earn a return on deferred amounts based on notional investments in the segregated accounts. Participants can elect lump sum distributions or annual installments of deferred balances during the participant's employment or upon retirement. As of December 31, 2023 and 2022, our liability to participants under these deferred compensation plans was $24.6 million and $20.6 million. Company contributions to these plans were $1.2 million, $0.9 million and $1.1 million for the years ended December 31, 2023, 2022 and 2021. Gains or (losses) recognized due to changes in our payment obligations in connection with these plans amounted to ($3.3 million), $3.1 million, and ($2.2 million) for the years ended December 31, 2023, 2022 and 2021.
Stock-Based Compensation
Stock-based compensation awards are measured at the grant-date fair value of the award and compensation expense is recognized on a straight-line basis over the applicable service or performance period. The service period may be limited to the period until such time that a recipient is retirement eligible as determined under the award agreement. Awards granted to employees eligible for retirement on the date of grant are expensed in the period of grant. We recognize the effects of award forfeitures as they occur.
Fair Value Measurements
Fair value is defined as the price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants. Three levels of inputs may be used to measure fair value:
Level 1 – Quoted prices are available in active markets for identical assets or liabilities as of the reported date. The types of assets and liabilities included in Level 1 are highly liquid and actively traded instruments with quoted prices, such as equities listed on the New York Stock Exchange and commodity derivative contracts listed on the New York Mercantile Exchange.
Level 2 – Pricing inputs are other than quoted prices in active markets but are either directly or indirectly observable as of the reported date. The types of assets and liabilities included in Level 2 are typically either comparable to actively traded securities or contracts, such as treasury securities with pricing interpolated from recent trades of similar securities, or priced with models using highly observable inputs, such as commodity options priced using observable forward prices and volatilities. 
Level 3 – Significant inputs to pricing have little or no observability as of the reporting date. The types of assets and liabilities included in Level 3 are those with inputs requiring significant management judgment or estimation and may include complex and subjective models and forecasts.
In instances where the determination of the fair value measurement is based on inputs from different levels within the hierarchy, the level in the hierarchy within which the entire fair value measurement falls is based on the lowest level input that is significant to the fair value measurement in its entirety.
Related Parties
The Otter Tail Corporation Foundation and Otter Tail Power Company Foundation are independent not-for-profit charitable entities affiliated with the Company and are not included in the consolidated financial statements of Otter Tail Corporation. Contribution obligations to the two foundations totaling $5.5 million and $4.3 million were recognized as of December 31, 2023 and 2022. Cash contributions paid to the two foundations during the years ended December 31, 2023, 2022 and 2021 were $4.3 million, $4.5 million, and $3.8 million.
Variable Interest Entity
In October 2012, the Coyote Station owners, including OTP, entered into an LSA with Coyote Creek Mining Company, LLC, a subsidiary of The North American Coal Corporation, for the purchase of lignite coal to meet the coal supply requirements of Coyote Station for the period beginning in May 2016 and ending in December 2040. The price per ton paid by the Coyote Station owners under the LSA reflects the cost of production, along with an agreed upon profit and capital charge. CCMC was formed for the purpose of mining coal to meet the coal fuel supply requirements of Coyote Station from May 2016 through December 2040 and, based on the terms of the LSA, is considered a variable interest entity (VIE) 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 would cover all costs of operations as well as future reclamation costs. The Coyote Station owners are required to buy certain assets of CCMC 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 CCMC because the Coyote Station owners are required to buy the membership interests of CCMC at the end of the contract term at equity value. Under current accounting standards, the primary beneficiary of a VIE is required to include the assets, liabilities, results of operations and cash flows of the VIE in its consolidated financial statements. No single owner of Coyote Station owns a majority interest in Coyote Station and none, individually, has the power to direct the activities that most significantly impact CCMC. Therefore, none of the owners individually, including OTP, is considered the primary beneficiary of the VIE and the Company is not required to include CCMC in its consolidated financial statements.
If the LSA terminates prior to the expiration of its term or the production period terminates prior to December 31, 2040 and the Coyote Station owners purchase all of the outstanding membership interests of CCMC, the owners will satisfy or, if permitted by CCMC’s applicable lenders, assume all of CCMC’s obligations owed to CCMC’s lenders under its loans and leases. The Coyote Station owners have limited rights to assign their rights and obligations under the LSA without the consent of CCMC’s lenders during any period in which CCMC’s obligations to its lenders remain outstanding. In the event the contract is terminated prior to the end of the term due to certain events, OTP’s maximum loss exposure, as a result of its involvement with CCMC, could be as high as $40 million, or OTP’s 35% share of CCMC’s unrecovered costs as of December 31, 2023, if recovery of such a loss is denied by regulatory authorities.
Recent Accounting Pronouncements
Segment Reporting. In November 2023, the Financial Accounting Standards Board (FASB) issued amended authoritative guidance codified in Accounting Standards Codification (ASC) 280, Segment Reporting. The amended guidance expands annual and interim disclosure requirements for reportable segments, primarily through expanded disclosures about significant segment expenses. The updated standard is effective for our annual periods beginning in 2024 and interim periods beginning in the first quarter of fiscal 2025. Adoption of the amended guidance must be applied retrospectively to all prior periods presented in the financial statements. We are currently evaluating the impact that the updated standard will have on our financial statement disclosures.
Income Taxes. In December 2023, the FASB issued amended authoritative guidance codified in ASC 740, Income Taxes. The amended guidance requires additional disaggregated information in effective tax rate reconciliation disclosures and additional disaggregated information about income taxes paid. The updated standard is effective for our annual periods beginning in 2025. The amended guidance is to be applied on a prospective basis with the option to apply the standard retrospectively. We are currently evaluating the impact that the updated standard will have on our financial statement disclosures.
v3.24.0.1
Segment Information
 12 Months Ended
Dec. 31, 2023
Segment Reporting [Abstract]  
Segment Information Segment Information
We classify our business into three segments, Electric, Manufacturing and Plastics, consistent with our business strategy, organizational structure and our internal reporting and review processes used by our chief operating decision maker to make decisions regarding allocation of resources, to assess operating performance and to make strategic decisions.
Electric includes the production, transmission, distribution and sale of electric energy in Minnesota, North Dakota and South Dakota by OTP. In addition, OTP is a participant in the MISO markets. OTP’s operations have been our primary business since 1907.
Manufacturing consists of businesses in the following manufacturing activities: contract machining, metal parts stamping, fabrication and painting, and production of plastic thermoformed horticultural containers, life science and industrial packaging, and material handling components. These businesses have manufacturing facilities in Georgia, Illinois and Minnesota and sell products primarily in the United States.
Plastics consists of businesses producing PVC pipe at plants in North Dakota and Arizona. The PVC pipe is sold primarily in the western half of the United States and Canada.
Certain assets, income and expenses are not allocated to our operating segments. Corporate operating results include items such as corporate staff and overhead costs, the results of our captive insurance company, gains or losses on our investments and returns on our cash equivalent investments. These items and others are excluded from the measurement of operating segment performance. Corporate assets consist primarily of cash, investments, prepaid expenses, and fixed assets. Corporate is not an operating segment, rather it is added to operating segment totals to reconcile to consolidated amounts.
Information for each segment and our unallocated corporate costs for the years ended December 31, 2023, 2022 and 2021 are as follows:
(in thousands)202320222021
Operating Revenue
Electric$528,359 $549,699 $480,321 
Manufacturing402,781 397,983 336,294 
Plastics418,026 512,527 380,229 
Total1,349,166 1,460,209 1,196,844 
Depreciation and Amortization
Electric75,330 72,050 71,343 
Manufacturing18,495 16,202 15,436 
Plastics4,027 4,205 4,354 
Corporate102 140 225 
Total97,954 92,597 91,358 
Operating Income (Loss)
Electric106,521 113,138 106,964 
Manufacturing29,140 29,065 24,114 
Plastics254,402 264,578 132,760 
Corporate(12,144)(16,342)(14,130)
Total377,919 390,439 249,708 
Interest Expense
Electric33,864 31,950 33,043 
Manufacturing2,295 2,796 2,239 
Plastics602 585 587 
Corporate916 685 1,902 
Total37,677 36,016 37,771 
Income Tax Expense (Benefit)
Electric1,648 5,065 1,663 
Manufacturing5,390 5,321 4,704 
Plastics66,066 68,688 34,374 
Corporate(3,806)(5,723)(4,689)
Total69,298 73,351 36,052 
Net Income (Loss)
Electric84,424 79,974 72,458 
Manufacturing21,454 20,950 17,186 
Plastics187,748 195,374 97,823 
Corporate565 (12,114)(10,698)
Total294,191 284,184 176,769 
Capital Expenditures
Electric240,695 147,869 140,031 
Manufacturing23,284 17,954 20,690 
Plastics23,029 5,245 11,040 
Corporate126 66 68 
Total$287,134 $171,134 $171,829 
The following provides the identifiable assets by segment and corporate assets as of December 31, 2023 and 2022:
(in thousands)20232022
Identifiable Assets
Electric$2,533,831 $2,351,961 
Manufacturing251,343 245,869 
Plastics164,179 126,318 
Corporate293,215 177,513 
Total$3,242,568 $2,901,661 
Concentrations
Our Plastics segment businesses use PVC resin as a critical component within their PVC pipe manufacturing process. There are a limited number of PVC resin suppliers in the U.S., and in 2023, we sourced all of our PVC resin needs from three vendors. Although there are a limited number of PVC resin suppliers, we believe that other suppliers could provide PVC resin on comparable terms. Additionally, most U.S. resin production plants are located in the Gulf Coast region. These plants are subject to the risk of damage and production shutdowns because of exposure to hurricanes or other extreme weather events that occur in this region. The loss of a key vendor, or any interruption or delay in the supply of PVC resin could cause production delays, a possible loss of sales, or result in increased costs to secure resin, all of which would adversely affect our operating results.
Entity-Wide Information
No single customer accounted for over 10% of our consolidated operating revenues for the years ended December 31, 2023, 2022 and 2021. All of our long-lived assets are located within the United States and substantially all of our operating revenues are from customers located within the United States.
v3.24.0.1
Revenue
 12 Months Ended
Dec. 31, 2023
Revenue from Contract with Customer [Abstract]  
Revenue Revenue
We present our operating revenues from external customers, in total and by amounts arising from contracts with customers and ARP arrangements, disaggregated by revenue source and segment for the years ended December 31, 2023, 2022 and 2021:
(in thousands)202320222021
Operating Revenues
Electric Segment
Retail: Residential$135,570 $143,888 $135,361 
Retail: Commercial and Industrial312,551 318,494 262,408 
Retail: Other7,719 7,918 7,715 
  Total Retail455,840 470,300 405,484 
Transmission52,555 52,213 48,835 
Wholesale12,459 18,539 17,936 
Other7,505 8,647 8,066 
Total Electric Segment528,359 549,699 480,321 
Manufacturing Segment
Metal Parts and Tooling351,267 338,865 283,527 
Plastic Products and Tooling41,395 49,080 40,231 
Scrap Metal10,119 10,038 12,536 
Total Manufacturing Segment402,781 397,983 336,294 
Plastics Segment
PVC Pipe418,026 512,527 380,229 
Total Operating Revenue1,349,166 1,460,209 1,196,844 
Less: Noncontract Revenues Included Above
Electric Segment - ARP Revenues(4,310)(9,266)(791)
Total Operating Revenues from Contracts with Customers$1,353,476 $1,469,475 $1,197,635 
v3.24.0.1
Receivables
 12 Months Ended
Dec. 31, 2023
Receivables [Abstract]  
Receivables Receivables
Receivables as of December 31, 2023 and 2022 are as follows:
(in thousands)20232022
Receivables
Trade$129,257 $112,126 
Other9,084 9,983 
Unbilled Receivables21,324 23,932 
Total Receivables159,665 146,041 
Less Allowance for Credit Losses2,522 1,648 
Receivables, net of allowance for credit losses$157,143 $144,393 
The following is a summary of activity in the allowance for credit losses for the years ended December 31, 2023 and 2022:
(in thousands)20232022
Beginning Balance$1,648 $1,836 
Additions Charged to Expense2,014 909 
Reductions for Amounts Written Off, Net of Recoveries
(1,140)(1,097)
Ending Balance$2,522 $1,648 
v3.24.0.1
Regulatory Matters
 12 Months Ended
Dec. 31, 2023
Regulatory Assets and Liabilities Disclosure [Abstract]  
Regulatory Matters Regulatory Matters
Regulatory Assets and Liabilities
The following presents our current and long-term regulatory assets and liabilities as of December 31, 2023 and 2022 and the period we expect to recover or refund such amounts:
Period of20232022
(in thousands)Recovery/RefundCurrentLong-TermCurrentLong-Term
Regulatory Assets
Pension and Other Postretirement Benefit Plans1
See below$154 $86,134 $— $88,354 
Alternative Revenue Program Riders2
Up to 2 years
3,719 158 5,679 2,508 
Asset Retirement Obligations1
Asset lives— 87 — 1,467 
Deferred Income TaxesAsset lives— 6,940 — — 
Fuel Clause Adjustments1
Up to 1 year
7,294 — 10,893 — 
Derivative Instruments1
Up to 1 year
4,210 — 7,130 — 
Other1
Various750 2,396 1,297 2,326 
Total Regulatory Assets16,127 95,715 24,999 94,655 
Regulatory Liabilities
Deferred Income TaxesAsset lives— 136,022 — 131,480 
Plant Removal ObligationsAsset lives— 117,030 8,509 105,733 
Fuel Clause Adjustments
Up to 1 year
11,350 — 365 — 
Alternative Revenue Program Riders
Up to 1 year
6,885 — 2,504 — 
North Dakota PTC Refunds
Asset lives— 12,011 — 7,136 
Pension and Other Postretirement Benefit PlansSee below6,138 11,307 5,589 — 
OtherVarious1,035 177 333 148 
Total Regulatory Liabilities$25,408 $276,547 $17,300 $244,497 
1Costs subject to recovery without a rate of return.
2Amount eligible for recovery includes an incentive or rate of return.
Pension and Other Postretirement Benefit Plans represent benefit costs and actuarial losses and gains subject to recovery or refund through rates as they are expensed or amortized. These unrecognized benefit costs and actuarial losses and gains are eligible for treatment as regulatory assets or liabilities based on their probable inclusion in future electric rates.
Alternative Revenue Program Riders regulatory assets and liabilities are revenues not yet collected from customers or amounts subject to refund, respectively, primarily due to investments in qualifying transmission, conservation, renewable resource, environmental and other generation assets, and the impact of decoupling.
Asset Retirement Obligations represent the difference in timing of recognition of expense arising from these obligations and the amount recovered from customers.
Fuel Clause Adjustments represent the under- or over-collection of fuel costs relative to the estimated cost of fuel included in customer rates, which will be collected from or returned to customers.
Derivative Instruments represent unrealized gains and losses recognized on derivative instruments. On final settlement of such instruments, any realized gains or losses are paid to or recovered from customers.
Deferred Income Taxes represent the revaluation of accumulated deferred income taxes arising from the change in the federal income tax rate in 2017. This amount is being refunded to customers over the estimated lives of the property assets from which the deferred income taxes originated.
Plant Removal Obligations represent amounts collected from customers to be used to cover actual removal costs as incurred.
North Dakota PTC Refunds represent PTCs earned from the Merricourt Wind Energy Center. These amounts are being allocated to customers over the life of the asset.
Other regulatory assets and liabilities include other amounts that we expect to recover from, or return to, customers in future periods, such as
the cost of abandoned projects, costs incurred in connection with recent rate cases, and other items.
North Dakota Rate Case
On November 2, 2023, OTP filed a request with the NDPSC for an increase in revenue recoverable under general rates in North Dakota. In its filing, OTP requested a net increase in annual revenue of $17.4 million, or 8.4%, based on an allowed rate of return on rate base of 7.85% and an allowed rate of return on equity of 10.6% on an equity ratio of 53.5% of total capital. Through this proceeding, OTP has proposed changes to the mechanism of cost and investment recovery, with recovery moving from riders into base rates. The filing also includes a proposal to implement a sales adjustment mechanism to address potential significant load additions or losses. The filing included an interim rate request of a net increase in annual revenue of $12.4 million, or 6.0%, which was approved by the NDPSC on December 13, 2023, and interim rates went into effect on January 1, 2024. These interim rate revenues, when collected, are subject to potential refund until the finalization of the rate case.
v3.24.0.1
Property, Plant and Equipment
 12 Months Ended
Dec. 31, 2023
Property, Plant and Equipment [Abstract]  
Property, Plant and Equipment Property, Plant and Equipment
Major classes of property, plant and equipment as of December 31, 2023 and 2022 include:
(in thousands)20232022
Electric Plant in Service  
Production$1,412,826 $1,343,097 
Transmission777,613 756,848 
Distribution654,704 612,716 
General144,738 131,718 
Electric Plant in Service2,989,881 2,844,379 
Construction Work in Progress137,212 113,932 
Total Gross Electric Plant3,127,093 2,958,311 
Less Accumulated Depreciation and Amortization851,148 859,988 
Net Electric Plant2,275,945 2,098,323 
Nonelectric Property, Plant and Equipment
Equipment233,571 218,770 
Buildings and Leasehold Improvements64,753 61,506 
Land13,600 13,652 
Nonelectric Property, Plant and Equipment311,924 293,928 
Construction Work in Progress38,062 15,170 
Total Gross Nonelectric Property, Plant and Equipment349,986 309,098 
Less Accumulated Depreciation and Amortization207,556 194,704 
Net Nonelectric Property, Plant and Equipment142,430 114,394 
Net Property, Plant and Equipment$2,418,375 $2,212,717 
Depreciation expense for the years ended December 31, 2023, 2022 and 2021 totaled $90.8 million, $84.4 million and $85.8 million.
The following table provides OTP’s ownership percentages and amounts included in the December 31, 2023 and 2022 consolidated balance sheets for OTP’s share of each of these jointly owned facilities:
 (dollars in thousands)Ownership
Percentage		Electric Plant
in Service		Construction
Work in
Progress		Accumulated
Depreciation		Net Plant
December 31, 2023     
Big Stone Plant53.9 %$341,683 $820 $(126,904)$215,599 
Coyote Station35.0 %188,656 104 (115,306)73,454 
Big Stone South–Ellendale 345 kV line50.0 %106,185 — (7,181)99,004 
Fargo–Monticello 345 kV line14.2 %78,184 — (11,238)66,946 
Big Stone South–Brookings 345 kV line50.0 %53,170 — (5,207)47,963 
Brookings–Southeast Twin Cities 345 kV line4.8 %26,409 83 (3,617)22,875 
Bemidji–Grand Rapids 230 kV line14.8 %16,331 — (3,568)12,763 
Jamestown– Ellendale 345 kV line50.0 %— 1,121 — 1,121 
Big Stone South–Alexandria 345 kV line40.0 %— 555 — 555 
Alexandria–Big Oaks 345 kV line
14.2 %— 343 — 343 
December 31, 2022
Big Stone Plant53.9 %$338,411 $557 $(118,044)$220,924 
Coyote Station35.0 %183,461 2,315 (111,666)74,110 
Big Stone South–Ellendale 345 kV line50.0 %106,185 — (5,587)100,598 
Fargo–Monticello 345 kV line14.2 %78,184 — (10,095)68,089 
Big Stone South–Brookings 345 kV line50.0 %53,041 — (4,406)48,635 
Brookings–Southeast Twin Cities 345 kV line4.8 %26,291 — (3,211)23,080 
Bemidji–Grand Rapids 230 kV line14.8 %16,331 — (3,318)13,013 
v3.24.0.1
Intangible Assets
 12 Months Ended
Dec. 31, 2023
Goodwill and Intangible Assets Disclosure [Abstract]  
Intangible Assets Intangible Assets
The following table summarizes our goodwill by segment as of December 31, 2023 and 2022: 
(in thousands)20232022
Manufacturing$18,270 $18,270 
Plastics19,302 19,302 
Total Goodwill$37,572 $37,572 
Our annual goodwill impairment testing, performed in the fourth quarters of 2023 and 2022, indicated no impairment existed as of the test date.
The following table summarizes the components of our intangible assets at December 31, 2023 and 2022:
(in thousands)Gross
Amount		Accumulated
Amortization		Net Carrying
Amount
December 31, 2023
Customer Relationships$22,491 $15,667 $6,824 
Other26 7 19 
Total22,517 15,674 6,843 
December 31, 2022
Customer Relationships22,491 14,568 7,923 
Other26 6 20 
Total$22,517 $14,574 $7,943 
Amortization expense for these intangible assets for each of the years ended December 31, 2023, 2022 and 2021 totaled $1.1 million.
Annual amortization expense for these intangible assets for the next five years is: 
(in thousands)20242025202620272028
Amortization Expense$1,100 $1,100 $1,092 $1,090 $554 
v3.24.0.1
Leases
 12 Months Ended
Dec. 31, 2023
Leases [Abstract]  
Leases Leases 
We lease rail cars, warehouse and office space, land, and certain office, manufacturing, material handling, and other equipment under varying terms and conditions. All leases are classified as operating leases.
The components of lease cost and lease cash flows for the years ended December 31, 2023, 2022, and 2021 are as follows:
(in thousands)202320222021
Lease Cost
Operating Lease Cost$6,309 $5,606 $5,298 
Variable Lease Cost1,433 1,386 1,020 
Short-Term Lease Cost2,525 1,517 1,465 
Total Lease Cost10,267 8,509 7,783 
Lease Cash Flows
Operating Cash Flows from Operating Leases$6,424 $5,592 $5,642 
A summary of operating lease right-of-use lease assets and lease liabilities as of December 31, 2023 and 2022 is as follows: 
(in thousands)20232022
Right of Use Lease Assets1
$16,788 $18,610 
Lease Liabilities
Current2
5,756 5,071 
Long-Term3
11,258 13,876 
Total Lease Liabilities$17,014 $18,947 
1Included in Other Noncurrent Assets in the consolidated balance sheets.
2Included in Other Current Liabilities in the consolidated balance sheets.
3Included in Other Noncurrent Liabilities in the consolidated balance sheets.
Operating lease assets obtained in exchange for new operating liabilities amounted to $3.6 million and $3.7 million for the years ended December 31, 2023 and 2022.
Maturities of lease liabilities as of December 31, 2023 for each of the next five years and in the aggregate thereafter are as follows:
(in thousands)Operating Leases
2024$6,473 
20255,357 
20263,068 
20272,196 
20281,059 
Thereafter368 
Total Lease Payments18,521 
Less: Interest1,507 
Present Value of Lease Liabilities$17,014 
The weighted-average remaining lease term and the weighted-average discount rate as of December 31, 2023 and 2022 are as follows:
20232022
Weighted-Average Remaining Lease Term (in years)3.44.2
Weighted-Average Discount Rate5.40 %4.73 %
v3.24.0.1
Short-Term and Long-Term Borrowings
 12 Months Ended
Dec. 31, 2023
Debt Disclosure [Abstract]  
Short-Term and Long-Term Borrowings Short-Term and Long-Term Borrowings
The following is a summary of our outstanding short- and long-term borrowings by borrower, OTC or OTP, as of December 31, 2023 and 2022:
20232022
(in thousands)OTCOTPTotalOTCOTPTotal
Short-Term Debt$— $81,422 $81,422 $— $8,204 $8,204 
Current Maturities of Long-Term Debt— — — — — — 
Long-Term Debt, net of current maturities79,849 744,210 824,059 79,798 744,023 823,821 
Total$79,849 $825,632 $905,481 $79,798 $752,227 $832,025 
Short-Term Debt
The following is a summary of our lines of credit as of December 31, 2023 and 2022:
20232022
(in thousands)Line LimitAmount OutstandingLetters
of Credit		Amount AvailableAmount Available
OTC Credit Agreement$170,000 $— $— $170,000 $170,000 
OTP Credit Agreement170,000 81,422 9,132 79,446 152,223 
Total$340,000 $81,422 $9,132 $249,446 $322,223 
OTC is party to a Fifth Amended and Restated Credit Agreement (the OTC Credit Agreement) and OTP is party to a Fourth Amended and Restated Credit Agreement (the OTP Credit Agreement). The agreements both provide for $170.0 million unsecured revolving lines of credit to support operations, fund capital expenditures, refinance certain indebtedness and provide for the issuance of letters of credit in an aggregate amount not to exceed $40.0 million under the OTC Credit Agreement and $50.0 million under the OTP Credit Agreement. Each credit facility includes an accordion provision allowing the borrower to increase the borrowing capacity under the facility, subject to certain conditions, up to $290.0 million and $250.0 million under the OTC Credit Agreement and OTP Credit Agreement, respectively.
Borrowings under each credit facility are subject to a variable rate of interest on outstanding balances and a commitment fee is charged based on the average unused amount available to be drawn under the respective facility. The variable rate of interest to be charged is based on a benchmark interest rate, either SOFR or a Base Rate, as defined in the credit agreements, selected by the borrower at the time of an advance, subject to the conditions of each agreement, plus an applicable credit spread. The credit spread ranges from zero to 2.00%, depending on the benchmark interest rate selected, and is subject to adjustment based on the credit ratings of the relevant borrower. The weighted-average interest rate on all outstanding borrowings as of December 31, 2023 and 2022 was 6.70% and 5.61%.
Each credit facility contains a number of restrictions on the borrower, including restrictions on the ability to merge, sell assets, make investments, create or incur liens on assets, guarantee the obligations of any other party and engage in transactions with related parties. The agreements also require the borrower to maintain various financial covenants, as further described below. Each credit facility expires on October 29, 2027.
Long-Term Debt
The following is a summary of outstanding long-term debt by borrower as of December 31, 2023 and 2022: 
(in thousands)
EntityDebt InstrumentRateMaturity20232022
OTCGuaranteed Senior Notes3.55%12/15/26$80,000 $80,000 
OTPSeries 2007C Senior Unsecured Notes6.37%08/02/2742,000 42,000 
OTPSeries 2013A Senior Unsecured Notes4.68%02/27/2960,000 60,000 
OTPSeries 2019A Senior Unsecured Notes 3.07%10/10/2910,000 10,000 
OTPSeries 2020A Senior Unsecured Notes3.22%02/25/3010,000 10,000 
OTPSeries 2020B Senior Unsecured Notes3.22%08/20/3040,000 40,000 
OTPSeries 2021A Senior Unsecured Notes2.74%11/29/3140,000 40,000 
OTPSeries 2007D Senior Unsecured Notes6.47%08/20/3750,000 50,000 
OTPSeries 2019B Senior Unsecured Notes3.52%10/10/3926,000 26,000 
OTPSeries 2020C Senior Unsecured Notes3.62%02/25/4010,000 10,000 
OTPSeries 2013B Senior Unsecured Notes5.47%02/27/4490,000 90,000 
OTPSeries 2018A Senior Unsecured Notes4.07%02/07/48100,000 100,000 
OTPSeries 2019C Senior Unsecured Notes3.82%10/10/4964,000 64,000 
OTPSeries 2020D Senior Unsecured Notes3.92%02/25/5015,000 15,000 
OTPSeries 2021B Senior Unsecured Notes3.69%11/29/51100,000 100,000 
OTPSeries 2022A Senior Unsecured Notes3.77%05/20/5290,000 90,000 
Total827,000 827,000 
Less:Unamortized Long-Term Debt Issuance Costs2,941 3,179 
Total Long-Term Debt Net of Unamortized Debt Issuance Costs$824,059 $823,821 
Our guaranteed and unsecured notes require the borrower to maintain various financial covenants, as further described below. These notes provide for prepayment options allowing for a full or partial prepayment at 100% of the principal amount so prepaid, together with unpaid accrued interest and a make-whole amount, as defined. These notes also include restrictions on the borrower, including its ability to merge, sell assets, create or incur liens on assets, guarantee the obligations of any other party and engage in transactions with related parties.
Aggregate maturities of long-term debt obligations at December 31, 2023 for each of the next five years are as follows:
(in thousands)20242025202620272028
Debt Maturities$— $— $80,000 $42,000 $— 
Financial Covenants
Certain of OTC's and OTP's short-term and long-term debt agreements require the borrower, whether OTC or OTP, to maintain certain financial covenants, including a maximum debt to total capitalization of 0.60 to 1.00, a minimum interest and dividend coverage ratio of 1.50 to 1.00, and a maximum level of priority indebtedness. As of December 31, 2023, OTC and OTP were in compliance with these financial covenants.
Guaranties
OTC's obligations under the terms of its Guaranteed Senior Notes are unconditionally and irrevocably guaranteed by its subsidiaries, Varistar Corporation, BTD Manufacturing, Inc., Northern Pipe Products, Inc., and Vinyltech Corporation.
v3.24.0.1
Employee Postretirement Benefits
 12 Months Ended
Dec. 31, 2023
Retirement Benefits [Abstract]  
Employee Postretirement Benefits Employee Postretirement Benefits
Pension Plan and Other Postretirement Benefits
The Company sponsors a noncontributory funded pension plan (the Pension Plan), an unfunded, nonqualified Executive Survivor and Supplemental Retirement Plan (ESSRP), both accounted for as defined benefit pension plans, and a postretirement healthcare plan accounted for as an other postretirement benefit plan.
The Pension Plan, which previously covered substantially all corporate and OTP employees, was closed to new employees in 2013. The plan provides retirement compensation to all covered employees at age 65, with reduced compensation in cases of retirement prior to age 62. Participants are fully vested after completing five years of vesting service. The plan assets consist of equity funds, fixed income funds, cash and cash equivalents and alternative investments. None of the plan assets are invested in common stock or debt securities of the Company.
The ESSRP, an unfunded plan, provides for defined benefit payments to executive officers and certain key management employees on their retirement for life, or to their beneficiaries on their death. The ESSRP was amended and restated in 2019 to i) freeze the participation in the
restoration retirement benefit component of the plan and ii) freeze benefit accruals under the restoration retirement benefit component of the plan for all participants of the plan except any participants deemed to be grandfathered participants.
The postretirement healthcare plan, closed to new participants in 2010, provides a portion of health insurance benefits for retired and covered corporate and OTP employees. To be eligible for retiree health insurance benefits, the employee must be 55 years of age with a minimum of 10 years of service. The plan is an unfunded plan and accordingly holds no plan assets.
Pension Plan Assets. We have established a Retirement Plans Administration Committee to develop and monitor our investment strategy for our Pension Plan assets. Our investment strategy includes the following objectives:
•The assets of the plan will be invested in accordance with all applicable laws in a manner consistent with fiduciary standards including Employee Retirement Income Security Act standards of 1974 (ERISA) (if applicable). Specifically:
◦The safeguards and diversity that a prudent investor would adhere to must be present in the investment program.
◦All transactions undertaken on behalf of the Pension Plan must be in the best interest of plan participants and their beneficiaries.
•The primary objective is to provide a source of retirement income for its participants and beneficiaries.
•The near-term primary financial objective is to improve and protect the funded status of the plan.
•A secondary financial objective is to minimize pension funding and expense volatility where possible.
We have developed an asset allocation target, measured at investment market value, to provide guideline percentages of investment mix. This investment mix is intended to achieve the financial objectives of the plan. The permitted range is a guide and will at times not reflect the actual asset allocation due to market conditions, actions of our investment managers and required cash flows to and from the Pension Plan.
The following table presents our target asset allocation permitted range along with the actual asset allocation as of December 31, 2023 and 2022:
 PermittedActual Allocation
Asset ClassRange20232022
Return Enhancement35 –60%48 %48 %
Risk Management40 –80%51 51 
Alternatives0 –20%1 1 
Total100 %100 %
Return Enhancement investments are those that seek to provide equity-like, long-term capital appreciation. Examples include equity securities, including dynamic asset allocation funds, and higher yielding fixed income securities, such as high yield bonds and emerging market debt.
Risk Management investments seek to decrease downside risk or act as a hedge against plan liabilities. Examples are cash and fixed income instruments.
Alternative investments seek to either provide return enhancement through long-term appreciation or risk management through decreased downside risk. The defining characteristic of these asset types is uncorrelated source of returns, less liquidity and private market access. Examples include investments in the SEI Energy Debt Collective Fund.
The following presents the fair value inputs classified within the fair value hierarchy used to measure Pension Plan assets at December 31, 2023 and 2022 and assets measured using the net asset value (NAV) practical expedient:
(in thousands)Level 1Level 2Level 3NAVTotal
December 31, 2023
Equity Funds$127,159 $— $— $— $127,159 
Fixed Income Funds167,604 — — — 167,604 
Hybrid Funds10,980 — — — 10,980 
U.S. Treasury Securities23,218 — — — 23,218 
SEI Energy Debt Collective Fund— — — 1,518 1,518 
Total328,961 — — 1,518 330,479 
December 31, 2022
Equity Funds124,327 — — — 124,327 
Fixed Income Funds156,424 — — — 156,424 
Hybrid Funds9,756 — — — 9,756 
U.S. Treasury Securities19,587 — — — 19,587 
SEI Energy Debt Collective Fund— — — 3,703 3,703 
Total$310,094 $— $— $3,703 $313,797 
The investments held by the SEI Energy Debt Collective Fund on December 31, 2023 and 2022 consist mainly of below investment grade high yield bonds and loans of U.S. energy companies which trade at a discount to fair value. Redemptions are allowed semi-annually with a 95-day notice
period, subject to fund director consent and certain gate, holdback and suspension restrictions. Subscriptions are allowed monthly with a three-year lock up on subscriptions. The fund’s assets are valued in accordance with valuations reported by the fund’s sub-advisor or the fund’s underlying investments or other independent third-party sources, although SEI in its discretion may use other valuation methods, subject to compliance with ERISA, as applicable. On an annual basis, as determined by the investment manager in its sole discretion, an independent valuation agent is retained to provide a valuation of the illiquid assets of the fund and of any other asset of the fund.
Funded Status. The following table provides a reconciliation of the changes in the fair value of plan assets and the actuarially computed benefit obligation for the years ended December 31, 2023 and 2022 and the funded status of the plans as of December 31, 2023 and 2022:
Pension Benefits (Pension Plan) Pension Benefits (ESSRP)Postretirement Benefits
(in thousands)202320222023202220232022
Change in Fair Value of Plan Assets:
Fair Value of Plan Assets at January 1$313,797 $387,212 $— $— $— $— 
Actual Return on Plan Assets34,196 (76,485)— — — — 
Company Contributions— 20,000 2,197 2,205 3,167 2,294 
Benefit Payments(17,514)(16,930)(2,197)(2,205)(8,900)(8,173)
Participant Premium Payments— — — — 5,733 5,879 
Fair Value of Plan Assets at December 31330,479 313,797 — — — — 
Change in Benefit Obligation:
Benefit Obligation at January 1308,055 416,697 35,624 46,840 49,947 69,311 
Service Cost3,698 6,576 72 195 565 1,338 
Interest Cost16,436 12,344 1,889 1,341 2,416 2,041 
Benefit Payments(17,514)(16,930)(2,197)(2,205)(8,900)(8,172)
Participant Premium Payments— — — — 5,733 5,879 
Plan Amendments— — — — (17,493)— 
Actuarial (Gain) Loss
8,126 (110,632)392 (10,547)(2,123)(20,450)
Benefit Obligation at December 31318,801 308,055 35,780 35,624 30,145 49,947 
Funded Status$11,678 $5,742 $(35,780)$(35,624)$(30,145)$(49,947)
Amounts Recognized in Consolidated Balance Sheets at December 31:
Noncurrent Assets$11,678 $5,742 $— $— $— $— 
Current Liabilities— — (2,679)(2,414)(2,469)(2,970)
Noncurrent Liabilities and Deferred Credits— — (33,101)(33,210)(27,676)(46,977)
Net Asset (Liability)$11,678 $5,742 $(35,780)$(35,624)$(30,145)$(49,947)
The accumulated benefit obligation of our Pension Plan was $288.8 million and $283.2 million as of December 31, 2023 and 2022. The accumulated benefit obligation of our ESSRP was $35.8 million and $35.6 million as of December 31, 2023 and 2022.
In 2023, the Company amended its postretirement healthcare plan to eliminate, for Medicare-eligible participants, the employer-sponsored group waiver medical plan and instead allow participants to select an individual medical plan through a private marketplace exchange. The Company now provides these plan participants with an annual reimbursement to subsidize their medical premiums. The effect of the plan amendment reduced the Company’s projected benefit obligation by $20.1 million. The reduced benefit obligation included a $2.6 million reduction attributable to an increase in the discount rate used to measure the plan liability, which was 6.06% at the time of the amendment, compared to 5.52% used at December 31, 2022. The $17.5 million of savings attributable to the plan change is being recognized as a reduction to expense over 4.8 years, the expected remaining service period to retirement-age eligibility for active participants.
The following assumptions were used to determine benefit obligations as of December 31, 2023 and 2022:
Pension Benefits (Pension Plan)Pension Benefits (ESSRP)Postretirement Benefits
 202320222023202220232022
Discount Rate5.57 %5.51 %5.53 %5.51 %5.53 %5.52 %
Long-Term Rate of Compensation Increase
n/an/a3.00 %3.00 %n/an/a
Participants up to Age 39(1)
4.50 %4.50 %n/an/an/an/a
Participants Ages 40 to 49(2)
4.50 %3.50 %n/an/an/an/a
Participants Age 50 and Older(3)
3.75 %2.75 %n/an/an/an/a
Healthcare Cost Immediate Trend Raten/an/an/an/a6.97 %7.50 %
Healthcare Cost Ultimate Trend Raten/an/an/an/a4.00 %4.00 %
Year the Rate Reaches the Ultimate Trend Raten/an/an/an/a20482048
(1) Amount reflects rate of compensation increases for both union and non-union employees.
(2) Amount reflects rate of compensation increases for union employees. The rate of compensation increases for non-union employees is 3.50%.
(3) Amount reflects rate of compensation increases for union employees. The rate of compensation increases for non-union employees is 3.00%.
The measurement of the plan asset or benefit obligation recognized for our Pension Plan, ESSRP and postretirement healthcare benefit plan included the following significant actuarial adjustments:
•For the Pension Plan, an increase in the discount rate in 2023 and 2022 reduced our obligation by $2.2 million and $117.1 million. Changes in retirement rate, percentage married, spouse age, benefit election, benefit commencement age and wage assumptions increased our benefit obligation in 2023 by $7.9 million. Changes in plan participant census data increased our benefit obligation by $3.1 million in 2023. Actual returns on Pension Plan assets in 2023 were $34.2 million, compared to an expected return of $25.9 million, impacting our obligation by $8.3 million.
•For the ESSRP, an increase in the discount rate in 2023 and 2022 reduced our obligation by $0.1 million and $10.2 million.
•For the postretirement healthcare plan, a plan amendment during 2023, as described above, decreased our benefit obligation by $17.5 million. An increase in the discount rate in 2023 and 2022 reduced our obligation by $1.3 million and $17.9 million. Revised estimates of healthcare cost trends and participant contribution assumptions increased the benefit obligation by $1.1 million in 2023.
Net Periodic Benefit Cost. A portion of service cost may be capitalized as a cost of self-constructed property, plant and equipment. When recognized in the consolidated statements of income, service cost is recognized within one of the components of operating expenses. Nonservice cost components of net periodic benefit cost may be deferred and recognized as a regulatory asset under the accounting guidance for regulated operations. When recognized in the consolidated statements of income, nonservice cost components are recognized as nonservice cost components of postretirement benefits.
The following table lists the components of net periodic benefit cost of our defined benefit pension plans and other postretirement benefits for the years ended December 31, 2023, 2022 and 2021:
Pension Benefits (Pension Plan)Pension Benefits (ESSRP)Postretirement Benefits
(in thousands)202320222021202320222021202320222021
Service Cost$3,698 $6,576 $7,462 $72 $195 $187 $565 $1,338 $1,722 
Interest Cost16,436 12,344 11,660 1,889 1,341 1,228 2,416 2,041 1,891 
Expected Return on Assets(25,914)(23,684)(22,359)— — — — — — 
Amortization of Prior Service Cost— — — — — — (6,649)(5,733)(5,733)
Amortization of Net Actuarial Loss— 7,865 10,914 — 567 620 — 3,063 3,774 
Net Periodic Benefit Cost$(5,780)$3,101 $7,677 $1,961 $2,103 $2,035 $(3,668)$709 $1,654 
The following table includes the impact of regulation on the recognition of periodic benefit cost arising from pension and other postretirement benefits for the years ended December 31, 2023, 2022 and 2021:
(in thousands)202320222021
Net Periodic Benefit Cost$(7,487)$5,913 $11,366 
Net Amount Amortized Due to the Effect of Regulation
1,225 1,121 21 
Net Periodic Benefit Cost Recognized$(6,262)$7,034 $11,387 
The following assumptions were used to determine net periodic benefit cost for the years ended December 31, 2023, 2022 and 2021:
Pension Benefits (Pension Plan)Pension Benefits (ESSRP)Postretirement Benefits
 202320222021202320222021202320222021
Discount Rate5.51 %3.03 %2.78 %5.51 %2.93 %2.61 %5.52 %3.01 %2.75 %
Long-Term Rate of Return on Plan Assets7.00 %6.30 %6.51 %n/an/an/an/an/an/a
Long-Term Rate of Compensation Increasen/an/an/a3.00 %3.00 %3.00 %n/an/an/a
Participants to Age 394.50 %4.50 %4.50 %n/an/an/an/an/an/a
Participants Ages 40 to 493.50 %3.50 %3.50 %n/an/an/an/an/an/a
Participants Age 50 and Older2.75 %2.75 %2.75 %n/an/an/an/an/an/a
We develop our estimated discount rate through the use of a hypothetical bond portfolio method. This method derives the discount rate from the average yield of a collection of high credit quality bonds which produce cash flows similar to our anticipated future benefit payments. We estimate the assumed long-term rate of return on plan assets based primarily on asset category studies using historical market return and volatility data with forward-looking estimates based on existing financial market conditions and forecasts of capital markets. Modest excess return expectations versus some market indices are incorporated into the return projections based on the actively managed structure of the investment programs and their records of achieving such returns historically.
The following table presents the amounts not yet recognized as components of net periodic benefit cost as of December 31, 2023 and 2022:
Pension Benefits (Pension Plan)Pension Benefits (ESSRP)Postretirement Benefits
(in thousands)202320222023202220232022
Regulatory Assets (Liabilities):
Unrecognized Prior Service Cost
$— $— $— $— $(18,845)$(8,400)
Unrecognized Actuarial Loss85,227 85,367 1,061 979 1,759 3,993 
Net Regulatory Assets (Liabilities)85,227 85,367 1,061 979 (17,086)(4,407)
Accumulated Other Comprehensive Income (Loss):
Unrecognized Prior Service Cost
— — — — 498 99 
Unrecognized Actuarial Gain (Loss)
1,994 1,978 (1,403)(1,093)707 818 
Total Accumulated Other Comprehensive Income (Loss)$1,994 $1,978 $(1,403)$(1,093)$1,205 $917 
Cash Flows. We did not make any contributions to our Pension Plan in 2023. We made discretionary contributions of $20.0 million and $10.0 million in 2022 and 2021. As of December 31, 2023, we had no minimum funding requirements for our Pension Plan. Contributions to our ESSRP and postretirement healthcare plan are equal to the benefits paid to plan participants.
The following reflects anticipated benefit payments to be paid in each of the next five years and in the aggregate for the five year period thereafter under our pension plans and postretirement healthcare plan:
(in thousands)202420252026202720282029-2033
Projected Pension Plan Benefit Payments$18,851 $19,274 $19,828 $20,318 $20,882 $110,291 
Projected ESSRP Benefit Payments2,747 2,697 2,823 2,994 2,938 14,437 
Projected Postretirement Benefit Payments2,469 2,497 2,544 2,547 2,476 12,045 
Total$24,067 $24,468 $25,195 $25,859 $26,296 $136,773 
401K Plan
We sponsor a 401K plan for the benefit of all corporate and subsidiary company employees. Contributions made to these plans totaled $7.8 million for 2023, $6.7 million for 2022 and $6.5 million for 2021.
v3.24.0.1
Asset Retirement Obligations
 12 Months Ended
Dec. 31, 2023
Asset Retirement Obligation Disclosure [Abstract]  
Asset Retirement Obligations Asset Retirement Obligations
We have recognized Asset Retirement Obligations (AROs) related to our coal-fired generation plants, natural gas combustion turbines, solar facility, and wind turbines. The cost of AROs include items such as site restoration, closure of ash pits, and removal of certain structures, generators, asbestos and storage tanks. We have other legal obligations associated with the retirement of a variety of other long-lived tangible assets used in electric operations where the estimated settlement costs are individually and collectively immaterial. We have no assets legally restricted for the settlement of any AROs. As of December 31, 2023 and 2022, $0.1 million and $2.7 million, respectively, was included in other current liabilities and $36.4 million and $22.5 million, respectively, was included in other noncurrent liabilities in the consolidated balance sheets related to AROs.
A reconciliation of the carrying amounts of AROs for the years ended December 31, 2023 and 2022 is as follows: 
(in thousands)20232022
Beginning Balance$25,182 $24,191 
New Obligations Recognized4,506 — 
Adjustments Due to Revisions in Cash Flow Estimates8,394 — 
Accrued Accretion1,191 991 
Settlements(2,796)— 
Ending Balance$36,477 $25,182 
v3.24.0.1
Income Taxes
 12 Months Ended
Dec. 31, 2023
Income Tax Disclosure [Abstract]  
Income Taxes Income Taxes
Income before income taxes for the years ended December 31, 2023, 2022 and 2021 consists entirely of domestic earnings.
The provision for income taxes charged to income for the years ended December 31, 2023, 2022 and 2021 consisted of the following:
(in thousands)202320222021
Current
Federal Income Taxes$41,253 $31,949 $6,806 
State Income Taxes15,126 9,568 939 
Deferred
Federal Income Taxes9,832 22,480 18,180 
State Income Taxes3,676 9,943 10,716 
Tax Credits
North Dakota Wind Tax Credit Amortization, Net of Federal Tax(586)(586)(586)
Investment Tax Credit Amortization(3)(3)(3)
Total$69,298 $73,351 $36,052 
The reconciliation of the statutory federal income tax rate to our effective tax rate for each of the years ended December 31, 2023, 2022 and 2021 is as follows:
202320222021
Income Taxes at Federal Statutory Rate$76,332 21.0 %$75,082 21.0 %$44,692 21.0 %
Increases (Decreases) in Tax from:
State Taxes on Income, Net of Federal Tax14,429 4.0 15,049 4.2 9,962 4.7 
Production Tax Credits (PTCs)(17,394)(4.8)(14,985)(4.2)(12,503)(5.9)
Amortization of Excess Deferred Income Taxes(2,205)(0.6)(1,625)(0.5)(4,262)(2.0)
North Dakota Wind Tax Credit Amortization, Net of Federal Tax(586)(0.2)(586)(0.2)(586)(0.3)
Other, Net(1,278)(0.3)416 0.2 (1,251)(0.6)
Income Taxes at Effective Tax Rate$69,298 19.1 %$73,351 20.5 %$36,052 16.9 %
PTCs, North Dakota wind tax credits, and excess deferred income taxes related to the federal tax rate reduction in the 2017 Tax Cuts and Jobs Act are returned to customers as a reduction of the rates they are charged and result in a reduction of operating revenues.
Deferred tax assets and liabilities were composed of the following on December 31, 2023 and 2022:
(in thousands)20232022
Deferred Tax Assets  
Employee Benefits$39,959 $39,216 
Regulatory Liabilities56,479 57,353 
Tax Credit Carryforwards
21,836 20,209 
Cost of Removal32,993 37,360 
Asset Retirement Obligations
9,494 6,557 
Net Operating Loss Carryforward
2,336 1,853 
Other11,310 5,550 
Total Deferred Tax Assets174,407 168,098 
Deferred Tax Liabilities
Differences Related to Property(347,885)(334,201)
Retirement Benefits Regulatory Asset(22,458)(22,789)
Pension Expense(24,875)(24,269)
Other(16,462)(8,141)
Total Deferred Tax Liabilities(411,680)(389,400)
Deferred Income Taxes$(237,273)$(221,302)
The following is a schedule of tax credits and tax net operating losses available as of December 31, 2023 and the respective periods of expiration:
(in thousands)Amount2024-20292030-20372038-2043
State Net Operating Losses$2,336 $211 $2,125 $— 
State Tax Credits21,836 — — 21,836 
The following table summarizes the activity for unrecognized tax benefits for the years ended December 31, 2023, 2022 and 2021:
(in thousands)202320222021
Balance on January 1$923 $827 $771 
Increases for tax positions taken during a prior period
596 44 11 
Increases for tax positions taken during the current period163 260 189 
Decreases due to settlements with taxing authorities— — — 
Decreases as a result of a lapse of applicable statutes of limitations(193)(208)(144)
Balance on December 31$1,489 $923 $827 
The balance of unrecognized tax benefits as of December 31, 2023 would reduce our effective tax rate if recognized. The total amount of unrecognized tax benefits as of December 31, 2023 is not expected to change significantly within the next 12 months. We classify interest and penalties on tax uncertainties as components of the provision for income taxes in the consolidated statements of income.
The Company and its subsidiaries file a consolidated U.S. federal income tax return and various state income tax returns. As of December 31, 2023, with limited exceptions, we are no longer subject to examinations by taxing authorities for tax years prior to 2020 for federal and North Dakota income taxes and prior to 2019 for Minnesota state income taxes.
v3.24.0.1
Commitments and Contingencies
 12 Months Ended
Dec. 31, 2023
Commitments and Contingencies Disclosure [Abstract]  
Commitments and Contingencies Commitments and Contingencies
Commitments
Construction and Other Commitments. As of December 31, 2023, we had commitments under contracts for construction project materials, equipment, plant maintenance, and other services extending into 2046 which totaled approximately $17.1 million.
Electric Utility Capacity and Energy Requirements. OTP has commitments for the purchase of capacity and energy requirements under contractual agreements, including wind power purchase agreements extending into 2048. Generally, the terms of OTP's wind power purchase agreements require OTP to purchase all of the electricity generated by a particular wind farm and do not include fixed or minimum payments. The required payments are variable and the amounts due are determined based upon the amount of electricity generated. Capacity and energy requirement costs under these agreements totaled $5.6 million, $13.1 million and $11.5 million for the years ended December 31, 2023, 2022 and 2021.
Coal Purchase Commitments. OTP has contracts providing for the purchase and delivery of its coal requirements. OTP’s current coal purchase agreement with CCMC for Coyote Station expires December 31, 2040. All of Coyote Station’s coal requirements for the period covered must be purchased under this agreement. The agreement is structured so that the price of the coal covers all of CCMC's operating, financing, and future
mine reclamation costs. In the table below we have estimated the future payments to be made under the terms of the agreement until its maturity. OTP has an agreement for the purchase of Big Stone Plant’s coal requirements through December 31, 2024. There is no fixed minimum purchase requirement, and no amounts for this agreement have been included in the table below; however, under this agreement all of Big Stone Plant’s coal requirements for the period covered must be purchased under this agreement. Coal purchase costs under these two agreements totaled $43.7 million, $45.1 million and $40.4 million for the years ended December 31, 2023, 2022 and 2021.
Land Easement Payments. OTP has commitments to make payments for land easements not classified as leases. The contractual terms of these easements are generally 99 years or do not have a stated maturity date, however, per the terms of the agreements, our requirement to make payment ends once we cease use of the land. As such, in the table below, we have included payments under these easements through the estimated useful lives of the facilities associated with the easement. The commitments under these arrangements extend into 2055 and total approximately $62.4 million. Land easement costs under these agreements totaled $1.8 million, $1.4 million and $1.3 million for the years ended December 31, 2023, 2022 and 2021.
Our future commitments as of December 31, 2023 were as follows:
(in thousands)Construction Program
and Other Commitments		Capacity and Energy
Requirements		Coal Purchase
Commitments		Land
 Easement
Payments
2024$4,374 $245 $24,691 $1,804 
20254,051 217 24,593 1,840 
20261,377 197 25,374 1,845 
2027594 197 25,786 1,882 
2028550 197 25,344 1,921 
Beyond 20286,165 3,939 359,610 53,107 
Total$17,111 $4,992 $485,398 $62,399 
Contingencies
FERC ROE. In November 2013 and February 2015, customers filed complaints with the FERC seeking to reduce the ROE component of the transmission rates that MISO transmission owners, including OTP, may collect under the MISO tariff rate. FERC's most recent order, issued on November 19, 2020, adopted a revised ROE methodology and set the base ROE at 10.02% (10.52% with an adder) effective for the fifteen-month period from November 2013 to February 2015 and on a prospective basis beginning in September 2016. The order also dismissed any complaints covering the period from February 2015 to May 2016. On August 9, 2022, the U.S. Court of Appeals for the District of Columbia Circuit vacated the FERC order citing a lack of reasoned explanation by FERC in its adoption of its revised ROE methodology as outlined in its November 2020 order. The U.S. Court of Appeals remanded the matter to FERC to reopen the proceedings.
Significant uncertainty exists as to how FERC will proceed on remand and there is no prescribed timeline under which FERC must act. We have deferred recognition and recorded a refund liability of $2.8 million as of December 31, 2023. This refund liability reflects our best estimate of amounts previously collected from customers under the MISO tariff rate that may be required to be refunded to customers once all regulatory and judicial proceedings are complete and a final ROE is established for the periods outlined above.
Regional Haze Rule (RHR). The RHR was adopted in an effort to improve visibility in national parks and wilderness areas. The RHR requires states, in coordination with the EPA and other governmental agencies, to develop and implement plans to achieve natural visibility conditions. The second RHR implementation period covers the years 2018-2028. States are required to submit a state implementation plan (SIP) to assess reasonable progress with the RHR and determine what additional emission reductions are appropriate, if any.
Coyote Station, OTP's jointly owned coal-fired power plant in North Dakota, is subject to assessment in the second implementation period under the North Dakota SIP. The NDDEQ submitted its SIP to the EPA for approval in August 2022. In its plan, the NDDEQ concluded it is not reasonable to require additional emission controls during this planning period. The EPA has previously expressed disagreement with the NDDEQ's recommendation to forgo additional emission controls and has indicated that such a plan is not likely to be accepted.
We cannot predict with certainty the impact the SIP may have on our business until the SIP has been approved or otherwise acted on by the EPA. However, significant emission control investments could be required and the recovery of such costs from customers would require regulatory approval. Alternatively, investments in emission control equipment may prove to be uneconomic and result in the early retirement or the sale of our interest in Coyote Station, subject to regulatory approval. We cannot estimate the ultimate financial effects such a retirement or sale may have on our consolidated operating results, financial position or cash flows, but such amounts could be material and the recovery of such costs in rates would be subject to regulatory approval.
Self-Funding of Transmission Upgrades. The FERC has granted transmission owners within MISO the unilateral authority to determine the funding mechanism for interconnection transmission upgrades that are necessary to accommodate new generation facilities connecting to the electrical grid. Under existing FERC orders, transmission owners can unilaterally determine whether the generator pays the transmission owner in advance for the transmission upgrade or, alternatively, the transmission owner can elect to fund the upgrade and recover over time from the generator the cost of and a return on the upgrade investment (a self-funding). FERC’s orders granting transmission owners this unilateral funding authority has been judicially contested on the basis that transmission owners may be motivated to discriminate among generators in making
funding determinations. In the most recent judicial hearing, the petitioners argued to the U.S. Court of Appeals for the District of Columbia that FERC did not comply with a previous judicial order to fully develop a record regarding the risk of discrimination and the financial risk absorbed by transmission owners for generator-funded upgrades. On December 2, 2022, the Court of Appeals ruled in favor of the petitioners remanding the matter to FERC, instructing the agency to adequately explain the basis of its orders. The Court of Appeals decision did not vacate transmission owners’ unilateral funding authority.
OTP, as a transmission owner in MISO, has exercised its authority and elected to self-fund previous transmission upgrades necessary to accommodate new system generation. Under such an election, OTP is recovering the cost of the transmission upgrade and a return on that investment from the generator over a contractual period of time. Should FERC, on remand from the Court of Appeals, eliminate transmission owners’ unilateral funding authority, on either a prospective or retrospective basis, our financial results would be impacted. We cannot at this time reasonably predict the outcome of this matter given the uncertainty as to how and when FERC may respond to the judicial remand.
Other Contingencies. We are party to litigation and regulatory enforcement matters arising in the normal course of business. We regularly analyze relevant information and, as necessary, estimate and record accrued liabilities for matters in which a loss is probable of occurring and can be reasonably estimated. We believe the effect on our consolidated operating results, financial position and cash flows, if any, for the disposition of all matters pending as of December 31, 2023 will not be material.
v3.24.0.1
Stockholders' Equity
 12 Months Ended
Dec. 31, 2023
Equity [Abstract]  
Stockholders' Equity Stockholders' Equity
Capital Structure
In addition to authorized and outstanding common stock, the Company has 1,500,000 authorized no par value cumulative preferred shares and 1,000,000 authorized no par value cumulative preference shares. No cumulative preferred or cumulative preference shares were outstanding at December 31, 2023 or 2022.
Shelf Registrations
On May 3, 2021, upon the expiration of a prior shelf registration, we filed a shelf registration statement with the SEC under which we may offer for sale, from time to time, either separately or together in any combination, equity, debt or other securities described in the shelf registration statement. The registration statement expires in May 2024. No shares were issued pursuant to the shelf registration in 2023.
On May 3, 2021, upon the expiration of a prior shelf registration, we filed a registration statement with the SEC for the issuance of up to 1,500,000 common shares under an Automatic Dividend Reinvestment and Share Purchase Plan, which provides shareholders, retail customers of OTP and other interested investors a method of purchasing our common shares by reinvesting their dividends and/or making optional cash investments. Shares purchased under the plan may be new issue common shares or common shares purchased on the open market. In 2023, we issued 105,663 common shares under this program and no proceeds were received, as all shares issued were purchased on the open market. As of December 31, 2023, 1,145,330 shares remained available for purchase or issuance under the plan. The shelf registration for the plan expires in May 2024.
Dividend Restrictions
OTC is a holding company with no significant operations of its own. The primary source of funds for payments of dividends to our shareholders is from intercompany distributions made by OTC's subsidiaries to OTC. As a result of certain statutory limitations or regulatory or financing agreements, restrictions could occur on the amount of distributions allowed to be made by OTC's subsidiaries. Both the OTC Credit Agreement and OTP Credit Agreement contain restrictions on the payment of cash dividends upon a default or event of default, including failure to maintain certain financial covenants. As of December 31, 2023, we were in compliance with these financial covenants.
Under the Federal Power Act, a public utility may not pay dividends from any funds properly included in a capital account. What constitutes “funds properly included in a capital account” is undefined in the Federal Power Act and the related regulations; however, the FERC has consistently interpreted the provision to allow dividends to be paid as long as i) the source of the dividends is clearly disclosed, ii) the dividend is not excessive and iii) there is no self-dealing on the part of corporate officials.
The MPUC indirectly limits the amount of dividends OTP can pay to OTC by requiring an equity-to-total-capitalization ratio between 48.3% and 59.1%, with total capitalization not to exceed $2.0 billion based on OTP’s capital structure requirements as of December 31, 2023. As of December 31, 2023, OTP’s equity-to-total-capitalization ratio including short-term debt was 54.2% and its net assets restricted from distribution totaled approximately $771.3 million.
v3.24.0.1
Accumulated Other Comprehensive Income (Loss)
 12 Months Ended
Dec. 31, 2023
Equity [Abstract]  
Accumulated Other Comprehensive Income (Loss) Accumulated Other Comprehensive Income (Loss)
The Company's other comprehensive income (loss) consists of unamortized actuarial losses and prior service costs related to pension and other postretirement benefits and unrealized gains and losses on marketable securities classified as available-for-sale. The income tax expense or benefit associated with amounts reclassified from accumulated other comprehensive income (loss) and reflected in the consolidated statement of income are recognized in the same period as the amounts are reclassified.
The following table shows the changes in accumulated other comprehensive Income (loss) for the years ended December 31, 2023, 2022 and 2021:
(in thousands)Pension and Other Postretirement BenefitsNet Unrealized Gain (Losses) on Available-for-Sale SecuritiesTotal
Balance, December 31, 2020
$(8,716)$209 $(8,507)
Other Comprehensive Income (Loss) Before Reclassifications, net of tax
1,638 (132)1,506 
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)541 
(1)
(64)
(2)
477 
Total Other Comprehensive Income (Loss)2,179 (196)1,983 
Balance, December 31, 2021
(6,537)13 (6,524)
Other Comprehensive Income (Loss) Before Reclassifications, net of tax7,331 (433)6,898 
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)540 
(1)
1 
(2)
541 
Total Other Comprehensive Income (Loss)7,871 (432)7,439 
Balance, December 31, 2022
1,334 (419)915 
Other Comprehensive Income Before Reclassifications, net of tax
59 180 239 
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)(18)
(1)
12 
(2)
(6)
Total Other Comprehensive Income
41 192 233 
Balance, December 31, 2023
$1,375 $(227)$1,148 
(1) Included in the computation of net periodic pension and other postretirement benefit costs. See Note 10 for further information.
(2) Included in other income (expense), net on the accompanying consolidated statements of income.
v3.24.0.1
Share-Based Payments
 12 Months Ended
Dec. 31, 2023
Share-Based Payment Arrangement [Abstract]  
Share-Based Payments Share-Based Payments
Employee Stock Purchase Plan
The 1999 Employee Stock Purchase Plan authorizes the issuance of 1,400,000 common shares, allowing eligible employees to purchase our common shares through payroll withholding at a discount of up to 15% off the market price at the end of each six-month purchase period. Employee withholding amounts may not be less than $10 or more than $2,000 per month, subject to certain limitations, as described in the plan. A plan participant may cease making payroll deductions at any time. A participant may not purchase more than 2,000 shares in a given six month purchase period under the plan and may not purchase more than $25,000 (fair market value) of common shares under the plan and all other purchase plans (if any) in a calendar year. A participant may withdraw from the plan at any time and elect to receive the balance of their contributions to the plan that have not yet been used to purchase shares. Shares purchased under the plan are automatically enrolled in the Company's dividend reinvestment plan. Shares purchased under the plan may not be assigned, transferred, pledged, or otherwise disposed, except for certain situations allowed by the plan, such as upon death, for a period of 18 months after purchase. At our discretion, shares purchased under the plan can be either new issue shares or shares purchased in the open market. The plan shall automatically terminate when all of the shares authorized under the plan have been issued.
We recognize the 15% discount to the fair market value of the purchased shares as stock-based compensation expense, which amounted to $0.3 million, $0.3 million and $0.2 million for the years ended December 31, 2023, 2022 and 2021. For the years ended December 31, 2023, 2022 and 2021 the amount of shares issued under the plan amounted to 26,348, 26,420 and 27,975 shares. As of December 31, 2023, there were 237,367 shares available for purchase under the plan.
Share-Based Compensation Plan
The 2023 Stock Incentive Plan, which was approved by our shareholders in April 2023, authorizes the issuance of 979,891 common shares, including 500,000 newly requested common shares, for the granting of stock options, stock appreciation rights, restricted stock, restricted stock units, dividend equivalents, performance awards and other stock-based awards. In addition, common shares subject to any outstanding awards under our prior stock incentive plans that are forfeited, canceled or reacquired by the Company will become available for re-issuance under the 2023 Stock Incentive Plan. As of December 31, 2023, 943,192 shares were available for issuance under the plan. The plan terminates on April 17, 2033.
We grant restricted stock awards to our employees and members of our Board of Directors and stock performance awards to our executive officers and certain other key employees as part of our long-term compensation and retention program. Stock-based compensation cost, recognized within operating expenses in the consolidated statements of income, amounted to $7.4 million, $6.6 million and $6.7 million for the years ended December 31, 2023, 2022 and 2021. The related income tax benefit recognized for these periods amounted to $1.6 million, $1.7 million and $1.8 million.
Restricted Stock Awards. Restricted stock awards are granted to executive officers and other key employees and members of the Company's Board of Directors. The awards vest, depending on award recipient, either ratably over a period of three to four years or cliff vest after four years. Vesting is accelerated in certain circumstances, including upon retirement. Awards granted to members of the Board of Directors are issued and outstanding upon grant and carry the same voting and dividend rights of unrestricted outstanding common stock. Awards granted to executive officers and other key employees are eligible to receive dividend equivalent payments during the vesting period, subject to forfeiture under the terms of the agreement, but such awards are not issued or outstanding upon grant and do not provide for voting rights.
The grant-date fair value of each restricted stock award is determined based on the market price of the Company's common stock on the date of grant adjusted to exclude the value of dividends for those awards that do not receive dividend or dividend equivalent payments during the vesting period.
The following is a summary of restricted stock award activity for the year ended December 31, 2023:
SharesWeighted-Average
Grant-Date
Fair Value
Nonvested, Beginning of Year141,551 $49.83 
Granted55,205 68.03 
Vested(45,493)50.02 
Forfeited(2,350)52.02 
Nonvested, End of Year148,913 $56.48 
The weighted-average grant-date fair value of granted awards was $68.03, $59.95 and $43.55 during the years ended December 31, 2023, 2022 and 2021. The fair value of vested awards was $3.1 million, $3.0 million and $2.1 million during the years ended December 31, 2023, 2022 and 2021. As of December 31, 2023, there was $3.4 million of unrecognized compensation cost for unvested restricted stock awards to be recognized over a weighted-average period of 1.7 years.
Stock Performance Awards. Stock performance awards are granted to executive officers and certain other key employees. The awards vest at the end of a three-year performance period. The number of common shares awarded, if any, at the end of the performance period ranges from zero to 150% of the target amount based on two performance measures: i) total shareholder return relative to a peer group (TSR component) and ii) return on equity (ROE component). The awards have no voting or dividend rights during the vesting period. Vesting of the awards is accelerated in certain circumstances, including upon retirement. The amount of common shares awarded on an accelerated vesting is based on actual performance at the end of the performance period.
The grant-date fair value of the ROE component of the stock performance awards granted during the years ended December 31, 2023, 2022 and 2021 was determined using the grant date stock price and a discounted cash flow analysis to adjust for expected unearned dividends during the vesting period. The grant-date fair value of the TSR component of the stock performance awards granted during the years ended December 31, 2023, 2022 and 2021 was determined using a Monte Carlo fair value simulation model incorporating the following assumptions:
202320222021
Risk-free interest rate4.15 %1.52 %0.18 %
Expected term (in years)3.003.003.00
Expected volatility34.00 %32.00 %32.00 %
Dividend yield2.50 %2.90 %3.60 %
The risk-free interest rate was derived from yields on U.S. government bonds of a similar term. The expected term of the award is equal to the three-year performance period. Expected volatility was estimated based on actual historical volatility of our common stock over a five-year period. Dividend yield was estimated based on historic and future yield estimates.
The following is a summary of stock performance award activity for the year ended December 31, 2023 (share amounts reflect awards at target):
 SharesWeighted-Average
Grant-Date
Fair Value
Nonvested, Beginning of Year189,800 $45.95 
Granted59,400 61.97 
Vested(55,000)47.79 
Forfeited— — 
Nonvested, End of Year194,200 $50.33 
The weighted-average grant-date fair value of granted awards was $61.97, $54.91 and $38.34 during the years ended December 31, 2023, 2022 and 2021. The fair value of vested awards was $5.3 million, $5.1 million and $2.5 million during the years ended December 31, 2023, 2022 and
2021. As of December 31, 2023, there was $0.4 million of unrecognized compensation cost of unvested stock performance awards to be recognized over a weighted-average period of 0.67 years.
v3.24.0.1
Earnings Per Share
 12 Months Ended
Dec. 31, 2023
Earnings Per Share [Abstract]  
Earnings Per Share Earnings Per Share
The numerator used in the calculation of both basic and diluted earnings per share is net income. The denominator used in the calculation of basic earnings per share is the weighted-average number of shares outstanding during the period. The denominator used in the calculation of diluted earnings per share is derived by adjusting basic shares outstanding for the dilutive effect of potential shares outstanding, which consist of shares associated with time and performance based stock awards and our employee stock purchase plan.
The following includes the computation of the denominator for basic and diluted weighted-average shares outstanding for the years ended December 31, 2023, 2022 and 2021:
(in thousands)202320222021
Weighted Average Common Shares Outstanding – Basic41,668 41,586 41,491 
Effect of Dilutive Securities:
Stock Performance Awards269 248 226 
Restricted Stock Awards100 95 87 
Employee Stock Purchase Plan Shares and Other2 2 14 
Dilutive Effect of Potential Common Shares371 345 327 
Weighted Average Common Shares Outstanding – Diluted42,039 41,931 41,818 
The amount of shares excluded from diluted weighted-average common shares outstanding because such shares were anti-dilutive was not material for the years ended December 31, 2023, 2022 and 2021.
v3.24.0.1
Derivative Instruments
 12 Months Ended
Dec. 31, 2023
Derivative Instruments and Hedging Activities Disclosure [Abstract]  
Derivative Instruments Derivative Instruments
OTP enters into derivative instruments to manage its exposure to future commodity price variability, specifically future wholesale energy and natural gas prices, and reduce volatility in prices for our retail electric customers. These derivative instruments are not designated as qualifying hedging transactions but provide for an economic hedge against future price variability. The instruments are recorded at fair value on the consolidated balance sheets, with changes in fair value recorded in the consolidated statements of income. However, in accordance with rate-making and cost recovery processes, we recognize a regulatory asset or liability to defer losses or gains from derivative activity until settlement of the associated derivative instrument.
As of December 31, 2023 and 2022 OTP had outstanding pay-fixed, receive-variable swap agreements with an aggregate notional amount of 187,400 and 295,000 megawatt-hours of electricity. The contracts outstanding as of December 31, 2023 had various settlement dates throughout 2024. As of December 31, 2023 and 2022, the fair value of these derivative instruments was $4.2 million and $7.1 million, which are included in other current liabilities on the consolidated balance sheets. During the years ended December 31, 2023 and 2022, contracts matured and were settled in an aggregate amount of a $16.5 million loss and a $1.0 million gain, respectively. Gains and losses recognized on the settlement of derivative instruments are returned to, or recovered from, our electric customers through fuel recovery mechanisms in each state. When recognized in the statement of income, these gains or losses are included in electric purchased power
v3.24.0.1
Fair Value Measurements
 12 Months Ended
Dec. 31, 2023
Fair Value Disclosures [Abstract]  
Fair Value Measurements Fair Value Measurements
The following tables present our assets measured at fair value on a recurring basis as of December 31, 2023 and 2022 classified by the input method used to measure fair value:
Level 1Level 2Level 3
December 31, 2023
Assets
Investments:
Money Market Funds$3,125 $— $— 
Mutual Funds7,771 — — 
Corporate Debt Securities— 1,579 — 
Government Debt Securities
— 7,724 — 
Total Assets10,896 9,303 — 
Liabilities
Derivative Instruments— 4,210 — 
Total Liabilities$— $4,210 $— 
December 31, 2022
Assets
Investments:
Money Market Funds$1,560 $— $— 
Mutual Funds5,503 — — 
Corporate Debt Securities— 1,434 — 
Government Debt Securities
— 7,327 — 
Total Assets$7,063 $8,761 $— 
Liabilities
Derivative Instruments— 7,130 — 
Total Liabilities
$— $7,130 $— 
The level 2 fair value measurements for government and corporate debt securities are determined on the basis of valuations provided by a third-party pricing service which utilizes industry accepted valuation models and observable market inputs to determine valuation. Some valuations or model inputs used by the pricing service may be based on broker quotes.
The level 2 fair value measurements for derivative instruments are determined by using inputs such as forward electric commodity prices, adjusted for location differences. These inputs are observable in the marketplace throughout the full term of the instrument, can be derived from observable data, or are supported by observable levels at which transactions are executed in the marketplace.
In addition to assets recorded at fair value on a recurring basis, we also hold financial instruments that are not recorded at fair value in the consolidated balance sheets but for which disclosure of the fair value of these financial instruments is provided. The following reflects the carrying value and estimated fair value of these assets and liabilities as of December 31, 2023 and 2022:
 December 31, 2023December 31, 2022
(in thousands)Carrying
Amount		Fair ValueCarrying
Amount		Fair Value
Assets:
Cash and Cash Equivalents$230,373 $230,373 $118,996 $118,996 
Total230,373 230,373 118,996 118,996 
Liabilities:
Short-Term Debt81,422 81,422 8,204 8,204 
Long-Term Debt824,059 710,839 823,821 681,615 
Total$905,481 $792,261 $832,025 $689,819 
The following methods and assumptions were used to estimate the fair value of each class of financial instruments:
Cash Equivalents: The carrying amount approximates fair value because of the short-term maturity of these instruments.
Short-Term Debt: The carrying amount approximates fair value because the debt obligations are short-term in nature and balances outstanding are subject to variable rates of interest which reset frequently, a Level 2 fair value input.
Long-Term Debt: The fair value of long-term debt is estimated based on current market indications for borrowings of similar maturities with similar terms, a Level 2 fair value input.
v3.24.0.1
Schedule I - Condensed Financial Information of Registrant
 12 Months Ended
Dec. 31, 2023
Condensed Financial Information Disclosure [Abstract]  
Schedule I - Condensed Financial Information of Registrant
SCHEDULE I - CONDENSED FINANCIAL INFORMATION OF REGISTRANT
OTTER TAIL CORPORATION (PARENT COMPANY)
CONDENSED BALANCE SHEETS
December 31,
(in thousands)20232022
Assets
Current Assets
Cash and Cash Equivalents$228,137 $119,246 
Accounts Receivable from Subsidiaries2,555 3,278 
Interest Receivable from Subsidiaries117 117 
Other977 1,045 
Total Current Assets231,786 123,686 
Investments in Subsidiaries1,725,584 1,463,998 
Notes Receivable from Subsidiaries78,900 78,900 
Deferred Income Taxes65,244 64,802 
Other Assets50,795 43,779 
Total Assets$2,152,309 $1,775,165 
Liabilities and Stockholders' Equity
Current Liabilities
Accounts Payable to Subsidiaries$7 $7 
Notes Payable to Subsidiaries568,672 420,363 
Other15,320 15,994 
Total Current Liabilities583,999 436,364 
Other Noncurrent Liabilities45,455 41,686 
Commitments and Contingencies
Capitalization
Long-Term Debt
79,849 79,798 
Common Stockholders' Equity1,443,006 1,217,317 
Total Capitalization1,522,855 1,297,115 
Total Liabilities and Stockholders' Equity$2,152,309 $1,775,165 
See accompanying notes to condensed financial statements.
OTTER TAIL CORPORATION (PARENT COMPANY)
CONDENSED STATEMENTS OF INCOME
Years Ended December 31,
(in thousands)202320222021
Income
Equity Income in Earnings of Subsidiaries$294,467 $296,833 $188,375 
Interest Income from Subsidiaries2,898 3,382 2,826 
Other Income10,496 466 1,290 
Total Income307,861 300,681 192,491 
Expense
Nonelectric Selling, General, and Administrative Expenses12,816 17,269 14,825 
Interest Expense
3,813 4,066 4,727 
Interest Expense from Subsidiaries
6 5 3 
Nonservice Cost Components of Postretirement Benefits1,063 1,023 1,097 
Total Expense17,698 22,363 20,652 
Income Before Income Taxes290,163 278,318 171,839 
Income Tax Benefit4,028 5,866 4,930 
Net Income$294,191 $284,184 $176,769 
See accompanying notes to condensed financial statements.
OTTER TAIL CORPORATION (PARENT COMPANY)
CONDENSED STATEMENTS OF CASH FLOWS
Years Ended December 31,
(in thousands)202320222021
Cash Flows from Operating Activities
Net Cash Provided by Operating Activities$77,139 $28,807 $60,695 
Cash Flows from Investing Activities
Investment in Subsidiaries(40,000)(50,000)— 
Debt Repaid by Subsidiaries— — 169 
Other, net(68)(1,695)(884)
Net Cash Used in Investing Activities(40,068)(51,695)(715)
Cash Flows from Financing Activities
Net (Repayments) Borrowings on Short-Term Debt— (22,637)(42,529)
Borrowings from Subsidiaries148,308 236,926 49,085 
Proceeds from Issuance of Common Stock— — 696 
Payments for Shares Withheld for Employee Tax Obligations(3,088)(2,942)(1,507)
Payments for Retirement of Long-Term Debt— — (169)
Dividends Paid(73,061)(68,755)(64,864)
Other, net(339)(461)(689)
Net Cash Provided by (Used in) Financing Activities71,820 142,131 (59,977)
Net Change in Cash and Cash Equivalents108,891 119,243 3 
Cash and Cash Equivalents at Beginning of Period119,246 3 — 
Cash and Cash Equivalents at End of Period$228,137 $119,246 $3 
 
See accompanying notes to condensed financial statements.
OTTER TAIL CORPORATION (PARENT COMPANY)
NOTES TO CONDENSED FINANCIAL STATEMENTS
Incorporated by Reference
OTC’s consolidated statements of comprehensive income and common shareholders’ equity in Part II, Item 8 are incorporated by reference.
Basis of Presentation
The condensed financial information of OTC is presented to comply with Rule 12-04 of Regulation S-X. The unconsolidated condensed financial statements do not reflect all of the information and notes normally included with financial statements prepared in accordance with generally accepted accounting principles. Therefore, these condensed financial statements should be read with the consolidated financial statements and related notes included in this report on Form 10-K.
OTC’s investments in subsidiaries are presented under the equity method of accounting. Under this method, the assets and liabilities of subsidiaries are not consolidated. The investments in net assets of the subsidiaries are recorded in the balance sheets. The income from operations of the subsidiaries is reported on a net basis as equity income in earnings of subsidiaries.
Related Party Transactions
Outstanding receivables from and payables to OTC's subsidiaries as of December 31, 2023 and 2022 are as follows:
(in thousands)Accounts
Receivable		Interest
Receivable		Long-Term
Notes
Receivable		Accounts
Payable		Current
Notes
Payable
December 31, 2023
Otter Tail Power Company$2,415 $— $— $7 $— 
Northern Pipe Products, Inc.— 7 5,000 — 56,917 
Vinyltech Corporation14 17 11,500 — 98,016 
BTD Manufacturing, Inc.— 78 52,000 — 6,291 
T.O. Plastics, Inc.36 15 10,400 — 980 
Varistar Corporation— — — — 406,468 
Otter Tail Assurance Limited90 — — — — 
 $2,555 $117 $78,900 $7 $568,672 
December 31, 2022
Otter Tail Power Company$3,016 $— $— $7 $— 
Northern Pipe Products, Inc.— 7 5,000 — 77,182 
Vinyltech Corporation— 18 11,500 — 90,425 
BTD Manufacturing, Inc.— 77 52,000 — 693 
T.O. Plastics, Inc.20 15 10,400 — 5,855 
Varistar Corporation— — — — 246,208 
Otter Tail Assurance Limited242 — — — — 
$3,278 $117 $78,900 $7 $420,363 
Dividends
Dividends paid to OTC (the Parent) from its subsidiaries were as follows:
(in thousands)202320222021
Cash Dividends Paid to Parent by Subsidiaries$72,982 $68,680 $64,790 
See OTC’s notes to consolidated financial statements in Part II, Item 8 for other disclosures.
v3.24.0.1
Schedule II - Valuation and Qualifying Accounts and Reserves
 12 Months Ended
Dec. 31, 2023
SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]  
Schedule II - Valuation and Qualifying Accounts and Reserves
SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS AND RESERVES
OTTER TAIL CORPORATION
Below is a summary of activity within valuation and qualifying accounts for the years ended December 31, 2023, 2022 and 2021:
(in thousands)Balance, January 1Charged to Cost and Expenses
Deductions 1, 2
Balance, December 31
Allowance for Credit Losses
2023$1,648 $2,014 $(1,140)$2,522 
20221,836 909 (1,097)1,648 
20213,215 93 (1,472)1,836 
Deferred Tax Asset Valuation Allowance
2023$— $— $— $— 
2022— — — — 
2021800 — (800)— 
1Amounts under Allowance for Credit Losses reflect deductions to the allowance for amounts written-off, net of recoveries.
2Amounts under Deferred Tax Asset Valuation Allowance reflect a release of a valuation allowance based on current expectations of the realizability of the associated deferred tax asset.
v3.24.0.1
Summary of Significant Accounting Policies (Policies)
 12 Months Ended
Dec. 31, 2023
Accounting Policies [Abstract]  
Basis of Accounting These consolidated financial statements are presented in accordance with U.S. generally accepted accounting principles and include the accounts of OTC and its wholly owned subsidiaries.
Principles of Consolidation All intercompany balances and transactions have been eliminated in consolidation except, as applicable, profits on sales to our regulated electric utility company from our nonregulated businesses, which is in accordance with the accounting requirements of regulated operations.
Use of Estimates
Use of Estimates
We use estimates based on the best information available in recording transactions and balances resulting from business operations. As better information becomes available, or actual amounts are known, the recorded estimates are revised. Consequently, operating results can be affected by revisions to prior accounting estimates.
Reclassifications
Reclassifications
Certain reclassifications of amounts previously reported have been made to the accompanying consolidated statements of cash flows to maintain consistency and comparability between periods presented. Other, net operating cash flows previously reported for the years ended December 31, 2022 and 2021, included $3.3 million of investment losses and $4.5 million of investment gains, respectively, which are presented separately in the current year, and excluded $1.7 million and $0.8 million of allowance for equity funds used during construction (AFUDC), which were previously presented separately. The reclassifications had no impact on previously reported net cash provided by operating activities, net cash used in investing activities, net cash used in financing activities, or cash and cash equivalents. Certain prior period amounts related to deferred tax assets and deferred tax liabilities included in footnote 12 have been reclassified to conform to the current year presentation.
Regulatory Accounting
Regulatory Accounting
Our regulated electric utility company, Otter Tail Power Company (OTP), is subject to regulation of rates and other matters by state utility commissions in Minnesota, North Dakota and South Dakota and by the FERC for certain interstate operations. OTP accounts for the financial effects of regulation in accordance with accounting guidance for regulated operations. This guidance allows for the recording of a regulatory asset for certain costs which otherwise would be recognized in the statement of income or comprehensive income based on an expectation that the cost will be recovered in future rates. This guidance also requires the recording of a regulatory liability for certain credits which would otherwise be recognized in the statement of income or comprehensive income based on an expectation that the amount will be returned to customers in future rates. Amounts recorded as regulatory assets and regulatory liabilities are generally recognized in the statements of income at the time they are reflected in customer rates. In the event OTP ceases to meet the criteria to apply the guidance for regulated operations, the regulatory assets and liabilities that no longer meet such criteria would be removed from the consolidated balance sheets and included in the consolidated statement of income as an expense or income item, or in the consolidated statement of comprehensive income as a loss or gain item, in the period in which the application of this guidance ceases.
Cash Equivalents
Cash Equivalents
We consider all highly liquid investments purchased with maturity dates of 90 days or less to be cash equivalents.
Concentration of Deposits
Concentration of Deposits
We hold deposits with financial institutions which potentially subject us to a concentration risk. These deposits are guaranteed by the Federal Deposit Insurance Corporation up to an insurance limit of $250,000. Currently, our cash deposits exceed federally insured levels.
Revenue from Contracts with Customer
Revenue from Contracts with Customers
Due to our diverse business operations, the recognition of revenue from contracts with customers depends on the product produced and sold or service performed. We recognize revenue from contracts with customers at prices that are fixed or determinable as evidenced by an agreement with the customer, when we have met our performance obligation under the contract and it is probable that we will collect the amount to which we are entitled in exchange for the goods or services transferred or to be transferred to the customer. Depending on the product produced and sold or service performed and the terms of the agreement with the customer, we recognize revenue either over time, in the case of delivery or transmission of electricity or related services or the production and storage of certain custom-made products, or at a point in time for the delivery of standardized products and other products made to customer specifications where the terms of the contract require transfer of the completed product. Provisions for sales returns, early payment discounts, and volume-based variable pricing incentives are recorded as reductions to revenue at the time revenue is recognized based on customer history, historical information and current trends. We include revenues received for shipping and handling in operating revenues. Expenses paid for shipping and handling are recorded as part of cost of products sold. Sales or other taxes collected from customers are excluded from operating revenues.
Electric Segment Revenues. Most Electric segment revenues are earned from the generation, transmission and sale of electricity to retail customers at rates approved by state regulatory commissions. OTP also earns revenue from the transmission of electricity for others over the transmission assets it owns separately, or jointly with other transmission service providers, under rate tariffs established by the independent transmission system operator and approved by the FERC. A third source of revenue for OTP comes from the generation and sale of electricity to wholesale customers at contract or market rates. Revenues from all these sources meet the criteria to be classified as revenue from contracts with customers and are recognized over time as energy is delivered or transmitted. Revenue is recognized based on the metered quantity of electricity delivered or transmitted at the applicable rates. For electricity delivered and consumed after a meter is read but prior to the end of the reporting period, OTP records revenue and an unbilled receivable based on estimates of the amount of energy delivered to the customer.
Manufacturing Segment Revenues. Our Manufacturing segment businesses earn revenue predominantly from the production and delivery of custom-made or standardized parts and products to customers across several industries and from the production and sale of tools and dies to other manufacturers. For the production and delivery of standardized products and other products made to customer specifications where the terms of the contract require transfer of the completed product, we have met our performance obligation and recognize revenue at the point in time when the product is shipped. At this point we have no further obligation to provide services related to such products. The shipping terms used in these transactions are free on board (FOB) shipping point.
Plastics Segment Revenues. Our Plastics segment businesses earn revenue predominantly from the sale and delivery of standardized PVC pipe products produced at their manufacturing facilities. Revenue from the sale of these products is recognized at the point in time when the product is shipped as there is no further obligation to provide services related to such products and the shipping terms are FOB shipping point. We have one customer within our Plastics segment for which we produce and store a product made to the customer’s specifications and design under a build and hold agreement. For sales to this customer, we recognize revenue as the custom-made product is produced, adjusting the amount of revenue for volume rebate variable pricing considerations we expect the customer will earn and applicable early payment discounts we expect the customer will take. Ownership of the pipe transfers to the customer prior to delivery and we are paid a negotiated fee for storage of the pipe. Revenue for storage of the pipe is recognized over time as the pipe is stored.
Alternative Revenue
Alternative Revenue
In addition to recognizing revenue from contracts with customers, our Electric segment business also records revenue under alternative revenue program (ARP) requirements. Certain rate rider mechanisms qualify as ARP revenues as they provide for adjustments to rates outside of a general rate case proceeding to encourage or incentivize investments in certain areas such as conservation, renewable energy, pollution reduction or control, improved infrastructure of the transmission grid or other programs that provide benefits to the general public under public policy, laws or regulations. ARP riders generally provide for the recovery of specified costs and investments and include an incentive component to provide the regulated utility with a return on amounts invested.
We accrue ARP revenue on the basis of cost incurred, investments made and returns on those investments that qualify for recovery through established riders. ARP revenue is disclosed separately from revenue from contracts with customers and we have elected to report ARP revenue on a net basis, whereby amounts initially recorded as ARP revenue in a period are presented net of the reversal of amounts previously recognized as ARP revenue that are reclassified and recorded as revenue from contracts with customers when such amounts are included in the price of electricity to customers.
Receivables and Allowance for Credit Losses
Receivables and Allowance for Credit Losses
We grant credit to our customers in the normal course of business with repayment terms generally ranging from 30 to 90 days after the invoice date. Late fees are assessed on certain receivables once they are 30 days past due. Unbilled receivables represent estimates of energy delivered to customers but not yet billed.
Receivables are stated at the billed or estimated unbilled amount less an allowance for estimated credit losses. An allowance for credit losses is established based on losses expected to occur over the contractual life of the receivable. We estimate an allowance for credit losses on our trade and unbilled receivables by evaluating historical aging and write-off history, adjusted for current and forecasted economic conditions, for groups of receivables that share similar economic characteristics. Other receivables are evaluated by reviewing individual accounts, considering aging, financial condition of the debtor, recent payment history and other relevant factors. Account balances are written-off in the period they are deemed to be uncollectible.
Inventories
Inventories
Inventories are valued at the lower of cost or net realizable value. Costs for fuel, material and supply inventories of our Electric segment are determined on an average cost basis. Costs for raw material, work in process and finished goods inventories of our Manufacturing and Plastics segments are determined on a first-in first-out (FIFO) basis.
Investments
Investments
We invest in and hold, through rabbi trusts, corporate-owned life insurance policies to provide future funding for obligations under our supplemental pension plan and a nonqualified deferred compensation plan. The polices are recorded at cash surrender value and there are no restrictions on our ability to surrender the policies.
We hold debt, mutual fund, and money market fund investments either as investments within our captive insurance entity or to provide future funding for obligations under nonqualified deferred compensation plans. These investments are recorded at fair value. Debt securities are deemed to be available-for-sale securities, accordingly unrealized gains and losses are generally excluded from earnings and recognized in accumulated other comprehensive income. We evaluate whether declines in fair value of debt securities below the cost basis are other-than-temporary. Declines in fair value deemed to be other-than-temporary result in the recognition of unrealized losses, or a portion thereof, in earnings. Unrealized gains and losses on mutual and money market funds are recognized in earnings immediately.
Property, Plant and Equipment
Property, Plant and Equipment
Electric plant is stated at original cost. The cost of additions includes contracted work, direct labor and materials, allocable overheads and AFUDC. The amount of interest capitalized to electric plant was $1.9 million in 2023, $0.9 million in 2022 and $0.6 million in 2021. The cost of depreciable units of property retired less salvage is charged to accumulated depreciation. Amounts recovered in rates for future removal costs are recorded as regulatory liabilities. Removal costs, when incurred, are charged against the regulatory liability. Maintenance, repairs and replacement of minor items are charged to operating expenses as incurred. The provisions for utility depreciation for financial reporting purposes are made on the straight-line method based on the estimated remaining service lives of the properties. Gains or losses on group asset dispositions are recorded to accumulated depreciation and impact current and future depreciation rates.
Property, plant and equipment of nonelectric operations are carried at historical cost and are depreciated on a straight-line basis over the assets’ estimated useful lives. The cost of additions includes contracted work, direct labor and materials, allocable overheads and capitalized interest. No interest was capitalized in 2023, 2022 or 2021. Maintenance and repairs are expensed as incurred. Gains or losses on asset dispositions are included in the determination of operating income.
Jointly Owned Facilities
Jointly Owned Facilities
OTP is a joint owner in two coal-fired steam-powered electric generation plants: Big Stone Plant near Big Stone City, South Dakota and Coyote Station near Beulah, North Dakota. OTP is also a joint owner, with other regional utilities, in five major transmission lines. OTP's interest in each jointly owned facility is reflected in the consolidated balance sheets on a pro-rata basis and OTP's share of direct revenue and expenses are included in operating revenues and expenses in the consolidated statements of income. Each participant in the jointly owned facilities finances their own investments.
Goodwill and Other Intangible Assets
Goodwill and Other Intangible Assets
Goodwill is recognized and initially measured as any excess of the acquisition-date consideration transferred in a business combination over amounts recognized for the net identifiable assets acquired. Goodwill is not amortized, but is tested for impairment annually, or more frequently if
an event occurs or circumstances change that would more likely than not result in an impairment of goodwill. Impairment testing is performed at the reporting unit level, which is defined as an operating segment or one level below an operating segment. We perform our impairment testing in the fourth quarter of each year and have identified three reporting units that carry a goodwill balance.
Our impairment testing includes both an optional qualitative assessment and the quantitative impairment assessment. Our qualitative assessment includes an analysis of relevant events and circumstances to determine if it is more likely than not that the fair value of the reporting unit exceeds its book value. If, after this assessment, we determine that it is not more likely than not that the fair value of a reporting unit is less than its carrying amount, no additional analysis is necessary. In contrast, if after the assessment we determine it is more likely than not that the fair value of a reporting unit is less than its carrying amount, or if we elect to skip the optional qualitative assessment, the quantitative impairment assessment is performed. The quantitative assessment is a single-step test that identifies both the existence of impairment and the amount of impairment loss by comparing the estimated fair value of a reporting unit to its carrying value, with any excess carrying value over the fair value being recognized as an impairment loss.
Intangible assets with finite lives, which primarily consist of customer relationships, are carried at estimated fair value at the time of acquisition less accumulated amortization. The costs of the intangible assets are amortized over their estimated useful lives, which generally range from 15 to 20 years.
Cloud Computing Costs
Cloud Computing Costs
We capitalize implementation costs incurred in cloud computing arrangements that are service contracts consistent with capitalized implementation costs incurred to develop or obtain internal-use software. Costs are amortized on a straight-line basis over the life of the associated contract. Capitalized implementation costs are amortized over periods up to ten years. Capitalized costs and related accumulated amortization are included in other noncurrent assets on the consolidated balance sheets.
Leases
Leases
We recognize right-of-use lease assets and a corresponding lease liability at the lease commencement date. The length of our lease agreements varies from less than one year to approximately ten years. We have elected to not record lease assets and liabilities for leases with a lease term at commencement of 12 months or less; such leases are expensed on a straight-line basis over the lease term. If a lease contains an option to extend the lease term and there is reasonable certainty the option will be exercised, the option is considered in the lease term at inception. We have elected to not separate non-lease components (e.g., common area maintenance) from lease components on real estate leases, accordingly the recognized lease asset and lease liability incorporate in their measurement payments for non-lease components. Certain leases include variable lease payments as the amounts are subject to change over the lease term. We are unable to determine the interest rate implicit in our leases thus we apply our incremental borrowing rate to capitalize the right-of-use asset and lease liability. We estimate our incremental borrowing rate by incorporating considerations of lease term and lessee entity.
Recoverability of Long-Lived Assets
Recoverability of Long-Lived Assets
We review our long-lived assets including, among other assets, property, plant and equipment, amortizing intangible assets and right-of-use lease assets, whenever events or changes in circumstances indicate the carrying amount of the assets may not be recoverable. We determine potential impairment by comparing the carrying amount of the assets with the net cash flows expected to be provided by operating activities of the business or related assets. If the sum of the expected future net cash flows is less than the carrying amount of the assets, an impairment loss would be recognized. Such an impairment loss would be measured as the amount by which the carrying amount exceeds the fair value of the asset.
Asset Retirement Obligation
Asset Retirement Obligations
Legal obligations related to the future retirement of long-lived assets are recognized as asset retirement obligations (ARO). An ARO is recognized in the period in which the legal obligation is incurred and the amount of the obligation can be reasonably estimated, with an offsetting increase to the associated long-lived asset. AROs are initially recognized at fair value and increased with the passage of time (accretion). ARO estimates are revised periodically with any adjustment reflected in the ARO and associated long-lived asset.
Income Taxes
Income Taxes
We use the asset and liability method to account for income taxes. Under this method, deferred tax assets and liabilities are recognized for the expected future tax consequences of all temporary differences between the carrying amounts of assets and liabilities and their respective tax bases. Deferred taxes are recorded using the tax rates scheduled by tax law to be in effect in the periods when the temporary differences reverse. Deferred tax assets are reduced by a valuation allowance when it is more likely than not that a portion or all of the deferred tax assets will not be realized. The realizability of deferred tax assets is determined by taking into consideration forecasts of future taxable income, the reversal of other existing temporary differences, available net operating loss carryforwards and available tax planning strategies. Changes in valuation allowances are included in the provision for income taxes in the period of the changes.
We recognize the tax effects of all tax positions that are more-likely-than-not to be sustained on audit based solely on the technical merits of those positions as of the balance sheet date. Changes in the recognition or measurement of such positions are recognized in the provision for income taxes in the period of the changes. We classify interest and penalties on tax uncertainties as components of the provision for income taxes.
We have elected to account for transferable tax credits as a component of our income tax provision. We recognize the benefit of PTCs as a reduction of income tax expense in the period the credit is generated, which corresponds to the period the energy production occurs. We apply the deferral method of accounting for ITCs and state wind energy credits. Under this method, ITCs and state wind energy credits are amortized as a reduction to income tax expense over the estimated useful lives of the underlying property that gave rise to the credit.
Deferred Compensation Plans
Deferred Compensation Plans
The Company sponsors two nonqualified deferred compensation plans for the benefit of executive officers and other select employees. Each plan allows participants to defer a specified amount or percentage of base wages or incentive compensation into the plan, subject to certain limitations. The Company, at its discretion, may make employer contributions to either plan during any annual period. Participant and employer deferred amounts are segregated into one or more accounts chosen by the participant. Participants earn a return on deferred amounts based on notional investments in the segregated accounts. Participants can elect lump sum distributions or annual installments of deferred balances during the participant's employment or upon retirement.
Stock-Based Compensation
Stock-Based Compensation
Stock-based compensation awards are measured at the grant-date fair value of the award and compensation expense is recognized on a straight-line basis over the applicable service or performance period. The service period may be limited to the period until such time that a recipient is retirement eligible as determined under the award agreement. Awards granted to employees eligible for retirement on the date of grant are expensed in the period of grant. We recognize the effects of award forfeitures as they occur.
Fair Value Measurements
Fair Value Measurements
Fair value is defined as the price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants. Three levels of inputs may be used to measure fair value:
Level 1 – Quoted prices are available in active markets for identical assets or liabilities as of the reported date. The types of assets and liabilities included in Level 1 are highly liquid and actively traded instruments with quoted prices, such as equities listed on the New York Stock Exchange and commodity derivative contracts listed on the New York Mercantile Exchange.
Level 2 – Pricing inputs are other than quoted prices in active markets but are either directly or indirectly observable as of the reported date. The types of assets and liabilities included in Level 2 are typically either comparable to actively traded securities or contracts, such as treasury securities with pricing interpolated from recent trades of similar securities, or priced with models using highly observable inputs, such as commodity options priced using observable forward prices and volatilities. 
Level 3 – Significant inputs to pricing have little or no observability as of the reporting date. The types of assets and liabilities included in Level 3 are those with inputs requiring significant management judgment or estimation and may include complex and subjective models and forecasts.
In instances where the determination of the fair value measurement is based on inputs from different levels within the hierarchy, the level in the hierarchy within which the entire fair value measurement falls is based on the lowest level input that is significant to the fair value measurement in its entirety.
Related Parties
Related Parties
The Otter Tail Corporation Foundation and Otter Tail Power Company Foundation are independent not-for-profit charitable entities affiliated with the Company and are not included in the consolidated financial statements of Otter Tail Corporation.
Variable Interest Entity
Variable Interest Entity
In October 2012, the Coyote Station owners, including OTP, entered into an LSA with Coyote Creek Mining Company, LLC, a subsidiary of The North American Coal Corporation, for the purchase of lignite coal to meet the coal supply requirements of Coyote Station for the period beginning in May 2016 and ending in December 2040. The price per ton paid by the Coyote Station owners under the LSA reflects the cost of production, along with an agreed upon profit and capital charge. CCMC was formed for the purpose of mining coal to meet the coal fuel supply requirements of Coyote Station from May 2016 through December 2040 and, based on the terms of the LSA, is considered a variable interest entity (VIE) 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 would cover all costs of operations as well as future reclamation costs. The Coyote Station owners are required to buy certain assets of CCMC 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 CCMC because the Coyote Station owners are required to buy the membership interests of CCMC at the end of the contract term at equity value. Under current accounting standards, the primary beneficiary of a VIE is required to include the assets, liabilities, results of operations and cash flows of the VIE in its consolidated financial statements. No single owner of Coyote Station owns a majority interest in Coyote Station and none, individually, has the power to direct the activities that most significantly impact CCMC. Therefore, none of the owners individually, including OTP, is considered the primary beneficiary of the VIE and the Company is not required to include CCMC in its consolidated financial statements.
If the LSA terminates prior to the expiration of its term or the production period terminates prior to December 31, 2040 and the Coyote Station owners purchase all of the outstanding membership interests of CCMC, the owners will satisfy or, if permitted by CCMC’s applicable lenders, assume all of CCMC’s obligations owed to CCMC’s lenders under its loans and leases. The Coyote Station owners have limited rights to assign their rights and obligations under the LSA without the consent of CCMC’s lenders during any period in which CCMC’s obligations to its lenders remain outstanding. In the event the contract is terminated prior to the end of the term due to certain events, OTP’s maximum loss exposure, as a result of its involvement with CCMC, could be as high as $40 million, or OTP’s 35% share of CCMC’s unrecovered costs as of December 31, 2023, if recovery of such a loss is denied by regulatory authorities.
Recent Accounting Pronouncements
Recent Accounting Pronouncements
Segment Reporting. In November 2023, the Financial Accounting Standards Board (FASB) issued amended authoritative guidance codified in Accounting Standards Codification (ASC) 280, Segment Reporting. The amended guidance expands annual and interim disclosure requirements for reportable segments, primarily through expanded disclosures about significant segment expenses. The updated standard is effective for our annual periods beginning in 2024 and interim periods beginning in the first quarter of fiscal 2025. Adoption of the amended guidance must be applied retrospectively to all prior periods presented in the financial statements. We are currently evaluating the impact that the updated standard will have on our financial statement disclosures.
Income Taxes. In December 2023, the FASB issued amended authoritative guidance codified in ASC 740, Income Taxes. The amended guidance requires additional disaggregated information in effective tax rate reconciliation disclosures and additional disaggregated information about income taxes paid. The updated standard is effective for our annual periods beginning in 2025. The amended guidance is to be applied on a prospective basis with the option to apply the standard retrospectively. We are currently evaluating the impact that the updated standard will have on our financial statement disclosures.
v3.24.0.1
Summary of Significant Accounting Policies (Tables)
 12 Months Ended
Dec. 31, 2023
Accounting Policies [Abstract]  
Schedule of Inventories
Inventories consist of the following as of December 31, 2023 and 2022:
(in thousands)20232022
Finished Goods$47,614 $43,812 
Work in Process26,354 31,766 
Raw Material, Fuel and Supplies75,733 70,374 
Total Inventories$149,701 $145,952 
Schedule of Investments
The following is a summary of our investments at December 31, 2023 and 2022:
(in thousands)20232022
Corporate-Owned Life Insurance Policies$42,287 $38,991 
Corporate and Government Debt Securities
9,303 8,761 
Mutual Funds7,771 5,503 
Money Market Funds3,125 1,560 
Other Investments30 30 
Total Investments$62,516 $54,845 
Schedule of Estimated Service Lives for Rate-Regulated and Nonelectric Assets
The estimated service lives for rate-regulated electric assets and nonelectric assets are included below:
 Service Life Range
(years)LowHigh
Electric Assets:  
Production Plant21114
Transmission Plant5175
Distribution Plant1070
General Plant556
Nonelectric Assets:
Equipment220
Buildings and Leasehold Improvements240
Schedule of Capitalized Cost and Related Accumulated Amortization Below are the amounts of capitalized cost and related accumulated amortization as of December 31, 2023 and 2022:
(in thousands)20232022
Cloud Computing Costs
$12,782 $9,024 
Accumulated Amortization
$(1,505)$(897)
Cloud Computing Costs, net
$11,277 $8,127 
v3.24.0.1
Segment Information (Tables)
 12 Months Ended
Dec. 31, 2023
Segment Reporting [Abstract]  
Schedule of Segment Reporting Information, by Segment
Information for each segment and our unallocated corporate costs for the years ended December 31, 2023, 2022 and 2021 are as follows:
(in thousands)202320222021
Operating Revenue
Electric$528,359 $549,699 $480,321 
Manufacturing402,781 397,983 336,294 
Plastics418,026 512,527 380,229 
Total1,349,166 1,460,209 1,196,844 
Depreciation and Amortization
Electric75,330 72,050 71,343 
Manufacturing18,495 16,202 15,436 
Plastics4,027 4,205 4,354 
Corporate102 140 225 
Total97,954 92,597 91,358 
Operating Income (Loss)
Electric106,521 113,138 106,964 
Manufacturing29,140 29,065 24,114 
Plastics254,402 264,578 132,760 
Corporate(12,144)(16,342)(14,130)
Total377,919 390,439 249,708 
Interest Expense
Electric33,864 31,950 33,043 
Manufacturing2,295 2,796 2,239 
Plastics602 585 587 
Corporate916 685 1,902 
Total37,677 36,016 37,771 
Income Tax Expense (Benefit)
Electric1,648 5,065 1,663 
Manufacturing5,390 5,321 4,704 
Plastics66,066 68,688 34,374 
Corporate(3,806)(5,723)(4,689)
Total69,298 73,351 36,052 
Net Income (Loss)
Electric84,424 79,974 72,458 
Manufacturing21,454 20,950 17,186 
Plastics187,748 195,374 97,823 
Corporate565 (12,114)(10,698)
Total294,191 284,184 176,769 
Capital Expenditures
Electric240,695 147,869 140,031 
Manufacturing23,284 17,954 20,690 
Plastics23,029 5,245 11,040 
Corporate126 66 68 
Total$287,134 $171,134 $171,829 
The following provides the identifiable assets by segment and corporate assets as of December 31, 2023 and 2022:
(in thousands)20232022
Identifiable Assets
Electric$2,533,831 $2,351,961 
Manufacturing251,343 245,869 
Plastics164,179 126,318 
Corporate293,215 177,513 
Total$3,242,568 $2,901,661 
v3.24.0.1
Revenue (Tables)
 12 Months Ended
Dec. 31, 2023
Revenue from Contract with Customer [Abstract]  
Schedule of Disaggregation of Revenue
We present our operating revenues from external customers, in total and by amounts arising from contracts with customers and ARP arrangements, disaggregated by revenue source and segment for the years ended December 31, 2023, 2022 and 2021:
(in thousands)202320222021
Operating Revenues
Electric Segment
Retail: Residential$135,570 $143,888 $135,361 
Retail: Commercial and Industrial312,551 318,494 262,408 
Retail: Other7,719 7,918 7,715 
  Total Retail455,840 470,300 405,484 
Transmission52,555 52,213 48,835 
Wholesale12,459 18,539 17,936 
Other7,505 8,647 8,066 
Total Electric Segment528,359 549,699 480,321 
Manufacturing Segment
Metal Parts and Tooling351,267 338,865 283,527 
Plastic Products and Tooling41,395 49,080 40,231 
Scrap Metal10,119 10,038 12,536 
Total Manufacturing Segment402,781 397,983 336,294 
Plastics Segment
PVC Pipe418,026 512,527 380,229 
Total Operating Revenue1,349,166 1,460,209 1,196,844 
Less: Noncontract Revenues Included Above
Electric Segment - ARP Revenues(4,310)(9,266)(791)
Total Operating Revenues from Contracts with Customers$1,353,476 $1,469,475 $1,197,635 
v3.24.0.1
Receivables (Tables)
 12 Months Ended
Dec. 31, 2023
Receivables [Abstract]  
Schedule of Accounts Receivable
Receivables as of December 31, 2023 and 2022 are as follows:
(in thousands)20232022
Receivables
Trade$129,257 $112,126 
Other9,084 9,983 
Unbilled Receivables21,324 23,932 
Total Receivables159,665 146,041 
Less Allowance for Credit Losses2,522 1,648 
Receivables, net of allowance for credit losses$157,143 $144,393 
Schedule of Activity in the Allowance for Credit Losses
The following is a summary of activity in the allowance for credit losses for the years ended December 31, 2023 and 2022:
(in thousands)20232022
Beginning Balance$1,648 $1,836 
Additions Charged to Expense2,014 909 
Reductions for Amounts Written Off, Net of Recoveries
(1,140)(1,097)
Ending Balance$2,522 $1,648 
v3.24.0.1
Regulatory Matters (Tables)
 12 Months Ended
Dec. 31, 2023
Regulatory Assets and Liabilities Disclosure [Abstract]  
Schedule of Regulatory Assets and Liabilities
The following presents our current and long-term regulatory assets and liabilities as of December 31, 2023 and 2022 and the period we expect to recover or refund such amounts:
Period of20232022
(in thousands)Recovery/RefundCurrentLong-TermCurrentLong-Term
Regulatory Assets
Pension and Other Postretirement Benefit Plans1
See below$154 $86,134 $— $88,354 
Alternative Revenue Program Riders2
Up to 2 years
3,719 158 5,679 2,508 
Asset Retirement Obligations1
Asset lives— 87 — 1,467 
Deferred Income TaxesAsset lives— 6,940 — — 
Fuel Clause Adjustments1
Up to 1 year
7,294 — 10,893 — 
Derivative Instruments1
Up to 1 year
4,210 — 7,130 — 
Other1
Various750 2,396 1,297 2,326 
Total Regulatory Assets16,127 95,715 24,999 94,655 
Regulatory Liabilities
Deferred Income TaxesAsset lives— 136,022 — 131,480 
Plant Removal ObligationsAsset lives— 117,030 8,509 105,733 
Fuel Clause Adjustments
Up to 1 year
11,350 — 365 — 
Alternative Revenue Program Riders
Up to 1 year
6,885 — 2,504 — 
North Dakota PTC Refunds
Asset lives— 12,011 — 7,136 
Pension and Other Postretirement Benefit PlansSee below6,138 11,307 5,589 — 
OtherVarious1,035 177 333 148 
Total Regulatory Liabilities$25,408 $276,547 $17,300 $244,497 
1Costs subject to recovery without a rate of return.
2Amount eligible for recovery includes an incentive or rate of return.
v3.24.0.1
Property, Plant and Equipment (Tables)
 12 Months Ended
Dec. 31, 2023
Property, Plant and Equipment [Abstract]  
Schedule of Property, Plant and Equipment
Major classes of property, plant and equipment as of December 31, 2023 and 2022 include:
(in thousands)20232022
Electric Plant in Service  
Production$1,412,826 $1,343,097 
Transmission777,613 756,848 
Distribution654,704 612,716 
General144,738 131,718 
Electric Plant in Service2,989,881 2,844,379 
Construction Work in Progress137,212 113,932 
Total Gross Electric Plant3,127,093 2,958,311 
Less Accumulated Depreciation and Amortization851,148 859,988 
Net Electric Plant2,275,945 2,098,323 
Nonelectric Property, Plant and Equipment
Equipment233,571 218,770 
Buildings and Leasehold Improvements64,753 61,506 
Land13,600 13,652 
Nonelectric Property, Plant and Equipment311,924 293,928 
Construction Work in Progress38,062 15,170 
Total Gross Nonelectric Property, Plant and Equipment349,986 309,098 
Less Accumulated Depreciation and Amortization207,556 194,704 
Net Nonelectric Property, Plant and Equipment142,430 114,394 
Net Property, Plant and Equipment$2,418,375 $2,212,717 
Schedule of Jointly Owned Utility Plants
The following table provides OTP’s ownership percentages and amounts included in the December 31, 2023 and 2022 consolidated balance sheets for OTP’s share of each of these jointly owned facilities:
 (dollars in thousands)Ownership
Percentage		Electric Plant
in Service		Construction
Work in
Progress		Accumulated
Depreciation		Net Plant
December 31, 2023     
Big Stone Plant53.9 %$341,683 $820 $(126,904)$215,599 
Coyote Station35.0 %188,656 104 (115,306)73,454 
Big Stone South–Ellendale 345 kV line50.0 %106,185 — (7,181)99,004 
Fargo–Monticello 345 kV line14.2 %78,184 — (11,238)66,946 
Big Stone South–Brookings 345 kV line50.0 %53,170 — (5,207)47,963 
Brookings–Southeast Twin Cities 345 kV line4.8 %26,409 83 (3,617)22,875 
Bemidji–Grand Rapids 230 kV line14.8 %16,331 — (3,568)12,763 
Jamestown– Ellendale 345 kV line50.0 %— 1,121 — 1,121 
Big Stone South–Alexandria 345 kV line40.0 %— 555 — 555 
Alexandria–Big Oaks 345 kV line
14.2 %— 343 — 343 
December 31, 2022
Big Stone Plant53.9 %$338,411 $557 $(118,044)$220,924 
Coyote Station35.0 %183,461 2,315 (111,666)74,110 
Big Stone South–Ellendale 345 kV line50.0 %106,185 — (5,587)100,598 
Fargo–Monticello 345 kV line14.2 %78,184 — (10,095)68,089 
Big Stone South–Brookings 345 kV line50.0 %53,041 — (4,406)48,635 
Brookings–Southeast Twin Cities 345 kV line4.8 %26,291 — (3,211)23,080 
Bemidji–Grand Rapids 230 kV line14.8 %16,331 — (3,318)13,013 
v3.24.0.1
Intangible Assets (Tables)
 12 Months Ended
Dec. 31, 2023
Goodwill and Intangible Assets Disclosure [Abstract]  
Schedule of Goodwill by Segment
The following table summarizes our goodwill by segment as of December 31, 2023 and 2022: 
(in thousands)20232022
Manufacturing$18,270 $18,270 
Plastics19,302 19,302 
Total Goodwill$37,572 $37,572 
Schedule of Components of Intangible Assets
The following table summarizes the components of our intangible assets at December 31, 2023 and 2022:
(in thousands)Gross
Amount		Accumulated
Amortization		Net Carrying
Amount
December 31, 2023
Customer Relationships$22,491 $15,667 $6,824 
Other26 7 19 
Total22,517 15,674 6,843 
December 31, 2022
Customer Relationships22,491 14,568 7,923 
Other26 6 20 
Total$22,517 $14,574 $7,943 
Schedule of Intangible Assets Future Amortization Expenses
Annual amortization expense for these intangible assets for the next five years is: 
(in thousands)20242025202620272028
Amortization Expense$1,100 $1,100 $1,092 $1,090 $554 
v3.24.0.1
Leases (Tables)
 12 Months Ended
Dec. 31, 2023
Leases [Abstract]  
Schedule of Lease Costs
The components of lease cost and lease cash flows for the years ended December 31, 2023, 2022, and 2021 are as follows:
(in thousands)202320222021
Lease Cost
Operating Lease Cost$6,309 $5,606 $5,298 
Variable Lease Cost1,433 1,386 1,020 
Short-Term Lease Cost2,525 1,517 1,465 
Total Lease Cost10,267 8,509 7,783 
Lease Cash Flows
Operating Cash Flows from Operating Leases$6,424 $5,592 $5,642 
Schedule of Assets And Liabilities, Lessee
A summary of operating lease right-of-use lease assets and lease liabilities as of December 31, 2023 and 2022 is as follows: 
(in thousands)20232022
Right of Use Lease Assets1
$16,788 $18,610 
Lease Liabilities
Current2
5,756 5,071 
Long-Term3
11,258 13,876 
Total Lease Liabilities$17,014 $18,947 
1Included in Other Noncurrent Assets in the consolidated balance sheets.
2Included in Other Current Liabilities in the consolidated balance sheets.
3Included in Other Noncurrent Liabilities in the consolidated balance sheets.
The weighted-average remaining lease term and the weighted-average discount rate as of December 31, 2023 and 2022 are as follows:
20232022
Weighted-Average Remaining Lease Term (in years)3.44.2
Weighted-Average Discount Rate5.40 %4.73 %
Schedule of Lessee, Operating Lease, Liability, Maturity
Maturities of lease liabilities as of December 31, 2023 for each of the next five years and in the aggregate thereafter are as follows:
(in thousands)Operating Leases
2024$6,473 
20255,357 
20263,068 
20272,196 
20281,059 
Thereafter368 
Total Lease Payments18,521 
Less: Interest1,507 
Present Value of Lease Liabilities$17,014 
v3.24.0.1
Short-Term and Long-Term Borrowings (Tables)
 12 Months Ended
Dec. 31, 2023
Debt Disclosure [Abstract]  
Schedule of Debt
The following is a summary of our outstanding short- and long-term borrowings by borrower, OTC or OTP, as of December 31, 2023 and 2022:
20232022
(in thousands)OTCOTPTotalOTCOTPTotal
Short-Term Debt$— $81,422 $81,422 $— $8,204 $8,204 
Current Maturities of Long-Term Debt— — — — — — 
Long-Term Debt, net of current maturities79,849 744,210 824,059 79,798 744,023 823,821 
Total$79,849 $825,632 $905,481 $79,798 $752,227 $832,025 
The following is a summary of outstanding long-term debt by borrower as of December 31, 2023 and 2022: 
(in thousands)
EntityDebt InstrumentRateMaturity20232022
OTCGuaranteed Senior Notes3.55%12/15/26$80,000 $80,000 
OTPSeries 2007C Senior Unsecured Notes6.37%08/02/2742,000 42,000 
OTPSeries 2013A Senior Unsecured Notes4.68%02/27/2960,000 60,000 
OTPSeries 2019A Senior Unsecured Notes 3.07%10/10/2910,000 10,000 
OTPSeries 2020A Senior Unsecured Notes3.22%02/25/3010,000 10,000 
OTPSeries 2020B Senior Unsecured Notes3.22%08/20/3040,000 40,000 
OTPSeries 2021A Senior Unsecured Notes2.74%11/29/3140,000 40,000 
OTPSeries 2007D Senior Unsecured Notes6.47%08/20/3750,000 50,000 
OTPSeries 2019B Senior Unsecured Notes3.52%10/10/3926,000 26,000 
OTPSeries 2020C Senior Unsecured Notes3.62%02/25/4010,000 10,000 
OTPSeries 2013B Senior Unsecured Notes5.47%02/27/4490,000 90,000 
OTPSeries 2018A Senior Unsecured Notes4.07%02/07/48100,000 100,000 
OTPSeries 2019C Senior Unsecured Notes3.82%10/10/4964,000 64,000 
OTPSeries 2020D Senior Unsecured Notes3.92%02/25/5015,000 15,000 
OTPSeries 2021B Senior Unsecured Notes3.69%11/29/51100,000 100,000 
OTPSeries 2022A Senior Unsecured Notes3.77%05/20/5290,000 90,000 
Total827,000 827,000 
Less:Unamortized Long-Term Debt Issuance Costs2,941 3,179 
Total Long-Term Debt Net of Unamortized Debt Issuance Costs$824,059 $823,821 
Schedule of Line of Credit Facilities
The following is a summary of our lines of credit as of December 31, 2023 and 2022:
20232022
(in thousands)Line LimitAmount OutstandingLetters
of Credit		Amount AvailableAmount Available
OTC Credit Agreement$170,000 $— $— $170,000 $170,000 
OTP Credit Agreement170,000 81,422 9,132 79,446 152,223 
Total$340,000 $81,422 $9,132 $249,446 $322,223 
Schedule of Maturities of Long-Term Debt
Aggregate maturities of long-term debt obligations at December 31, 2023 for each of the next five years are as follows:
(in thousands)20242025202620272028
Debt Maturities$— $— $80,000 $42,000 $— 
v3.24.0.1
Employee Postretirement Benefits (Tables)
 12 Months Ended
Dec. 31, 2023
Retirement Benefits [Abstract]  
Schedule of Target and Tactical Allocation of Plan Assets
The following table presents our target asset allocation permitted range along with the actual asset allocation as of December 31, 2023 and 2022:
 PermittedActual Allocation
Asset ClassRange20232022
Return Enhancement35 –60%48 %48 %
Risk Management40 –80%51 51 
Alternatives0 –20%1 1 
Total100 %100 %
Schedule of Allocation of Plan Assets
The following presents the fair value inputs classified within the fair value hierarchy used to measure Pension Plan assets at December 31, 2023 and 2022 and assets measured using the net asset value (NAV) practical expedient:
(in thousands)Level 1Level 2Level 3NAVTotal
December 31, 2023
Equity Funds$127,159 $— $— $— $127,159 
Fixed Income Funds167,604 — — — 167,604 
Hybrid Funds10,980 — — — 10,980 
U.S. Treasury Securities23,218 — — — 23,218 
SEI Energy Debt Collective Fund— — — 1,518 1,518 
Total328,961 — — 1,518 330,479 
December 31, 2022
Equity Funds124,327 — — — 124,327 
Fixed Income Funds156,424 — — — 156,424 
Hybrid Funds9,756 — — — 9,756 
U.S. Treasury Securities19,587 — — — 19,587 
SEI Energy Debt Collective Fund— — — 3,703 3,703 
Total$310,094 $— $— $3,703 $313,797 
Schedule of Changes in Projected Benefit Obligations and Changes in Plan Assets The following table provides a reconciliation of the changes in the fair value of plan assets and the actuarially computed benefit obligation for the years ended December 31, 2023 and 2022 and the funded status of the plans as of December 31, 2023 and 2022:
Pension Benefits (Pension Plan) Pension Benefits (ESSRP)Postretirement Benefits
(in thousands)202320222023202220232022
Change in Fair Value of Plan Assets:
Fair Value of Plan Assets at January 1$313,797 $387,212 $— $— $— $— 
Actual Return on Plan Assets34,196 (76,485)— — — — 
Company Contributions— 20,000 2,197 2,205 3,167 2,294 
Benefit Payments(17,514)(16,930)(2,197)(2,205)(8,900)(8,173)
Participant Premium Payments— — — — 5,733 5,879 
Fair Value of Plan Assets at December 31330,479 313,797 — — — — 
Change in Benefit Obligation:
Benefit Obligation at January 1308,055 416,697 35,624 46,840 49,947 69,311 
Service Cost3,698 6,576 72 195 565 1,338 
Interest Cost16,436 12,344 1,889 1,341 2,416 2,041 
Benefit Payments(17,514)(16,930)(2,197)(2,205)(8,900)(8,172)
Participant Premium Payments— — — — 5,733 5,879 
Plan Amendments— — — — (17,493)— 
Actuarial (Gain) Loss
8,126 (110,632)392 (10,547)(2,123)(20,450)
Benefit Obligation at December 31318,801 308,055 35,780 35,624 30,145 49,947 
Funded Status$11,678 $5,742 $(35,780)$(35,624)$(30,145)$(49,947)
Amounts Recognized in Consolidated Balance Sheets at December 31:
Noncurrent Assets$11,678 $5,742 $— $— $— $— 
Current Liabilities— — (2,679)(2,414)(2,469)(2,970)
Noncurrent Liabilities and Deferred Credits— — (33,101)(33,210)(27,676)(46,977)
Net Asset (Liability)$11,678 $5,742 $(35,780)$(35,624)$(30,145)$(49,947)
Schedule of Assumptions Used in Calculating Net Periodic Benefit Cost
The following assumptions were used to determine benefit obligations as of December 31, 2023 and 2022:
Pension Benefits (Pension Plan)Pension Benefits (ESSRP)Postretirement Benefits
 202320222023202220232022
Discount Rate5.57 %5.51 %5.53 %5.51 %5.53 %5.52 %
Long-Term Rate of Compensation Increase
n/an/a3.00 %3.00 %n/an/a
Participants up to Age 39(1)
4.50 %4.50 %n/an/an/an/a
Participants Ages 40 to 49(2)
4.50 %3.50 %n/an/an/an/a
Participants Age 50 and Older(3)
3.75 %2.75 %n/an/an/an/a
Healthcare Cost Immediate Trend Raten/an/an/an/a6.97 %7.50 %
Healthcare Cost Ultimate Trend Raten/an/an/an/a4.00 %4.00 %
Year the Rate Reaches the Ultimate Trend Raten/an/an/an/a20482048
(1) Amount reflects rate of compensation increases for both union and non-union employees.
(2) Amount reflects rate of compensation increases for union employees. The rate of compensation increases for non-union employees is 3.50%.
(3) Amount reflects rate of compensation increases for union employees. The rate of compensation increases for non-union employees is 3.00%.
The following assumptions were used to determine net periodic benefit cost for the years ended December 31, 2023, 2022 and 2021:
Pension Benefits (Pension Plan)Pension Benefits (ESSRP)Postretirement Benefits
 202320222021202320222021202320222021
Discount Rate5.51 %3.03 %2.78 %5.51 %2.93 %2.61 %5.52 %3.01 %2.75 %
Long-Term Rate of Return on Plan Assets7.00 %6.30 %6.51 %n/an/an/an/an/an/a
Long-Term Rate of Compensation Increasen/an/an/a3.00 %3.00 %3.00 %n/an/an/a
Participants to Age 394.50 %4.50 %4.50 %n/an/an/an/an/an/a
Participants Ages 40 to 493.50 %3.50 %3.50 %n/an/an/an/an/an/a
Participants Age 50 and Older2.75 %2.75 %2.75 %n/an/an/an/an/an/a
Schedule of Net Benefit Costs
The following table lists the components of net periodic benefit cost of our defined benefit pension plans and other postretirement benefits for the years ended December 31, 2023, 2022 and 2021:
Pension Benefits (Pension Plan)Pension Benefits (ESSRP)Postretirement Benefits
(in thousands)202320222021202320222021202320222021
Service Cost$3,698 $6,576 $7,462 $72 $195 $187 $565 $1,338 $1,722 
Interest Cost16,436 12,344 11,660 1,889 1,341 1,228 2,416 2,041 1,891 
Expected Return on Assets(25,914)(23,684)(22,359)— — — — — — 
Amortization of Prior Service Cost— — — — — — (6,649)(5,733)(5,733)
Amortization of Net Actuarial Loss— 7,865 10,914 — 567 620 — 3,063 3,774 
Net Periodic Benefit Cost$(5,780)$3,101 $7,677 $1,961 $2,103 $2,035 $(3,668)$709 $1,654 
The following table includes the impact of regulation on the recognition of periodic benefit cost arising from pension and other postretirement benefits for the years ended December 31, 2023, 2022 and 2021:
(in thousands)202320222021
Net Periodic Benefit Cost$(7,487)$5,913 $11,366 
Net Amount Amortized Due to the Effect of Regulation
1,225 1,121 21 
Net Periodic Benefit Cost Recognized$(6,262)$7,034 $11,387 
Schedule of Amounts Recognized in Balance Sheet
The following table presents the amounts not yet recognized as components of net periodic benefit cost as of December 31, 2023 and 2022:
Pension Benefits (Pension Plan)Pension Benefits (ESSRP)Postretirement Benefits
(in thousands)202320222023202220232022
Regulatory Assets (Liabilities):
Unrecognized Prior Service Cost
$— $— $— $— $(18,845)$(8,400)
Unrecognized Actuarial Loss85,227 85,367 1,061 979 1,759 3,993 
Net Regulatory Assets (Liabilities)85,227 85,367 1,061 979 (17,086)(4,407)
Accumulated Other Comprehensive Income (Loss):
Unrecognized Prior Service Cost
— — — — 498 99 
Unrecognized Actuarial Gain (Loss)
1,994 1,978 (1,403)(1,093)707 818 
Total Accumulated Other Comprehensive Income (Loss)$1,994 $1,978 $(1,403)$(1,093)$1,205 $917 
Schedule of Expected Benefit Payments
The following reflects anticipated benefit payments to be paid in each of the next five years and in the aggregate for the five year period thereafter under our pension plans and postretirement healthcare plan:
(in thousands)202420252026202720282029-2033
Projected Pension Plan Benefit Payments$18,851 $19,274 $19,828 $20,318 $20,882 $110,291 
Projected ESSRP Benefit Payments2,747 2,697 2,823 2,994 2,938 14,437 
Projected Postretirement Benefit Payments2,469 2,497 2,544 2,547 2,476 12,045 
Total$24,067 $24,468 $25,195 $25,859 $26,296 $136,773 
v3.24.0.1
Asset Retirement Obligations (Tables)
 12 Months Ended
Dec. 31, 2023
Asset Retirement Obligation Disclosure [Abstract]  
Schedule of Change in Asset Retirement Obligation
A reconciliation of the carrying amounts of AROs for the years ended December 31, 2023 and 2022 is as follows: 
(in thousands)20232022
Beginning Balance$25,182 $24,191 
New Obligations Recognized4,506 — 
Adjustments Due to Revisions in Cash Flow Estimates8,394 — 
Accrued Accretion1,191 991 
Settlements(2,796)— 
Ending Balance$36,477 $25,182 
v3.24.0.1
Income Taxes (Tables)
 12 Months Ended
Dec. 31, 2023
Income Tax Disclosure [Abstract]  
Schedule of Components of Income Tax Expense
The provision for income taxes charged to income for the years ended December 31, 2023, 2022 and 2021 consisted of the following:
(in thousands)202320222021
Current
Federal Income Taxes$41,253 $31,949 $6,806 
State Income Taxes15,126 9,568 939 
Deferred
Federal Income Taxes9,832 22,480 18,180 
State Income Taxes3,676 9,943 10,716 
Tax Credits
North Dakota Wind Tax Credit Amortization, Net of Federal Tax(586)(586)(586)
Investment Tax Credit Amortization(3)(3)(3)
Total$69,298 $73,351 $36,052 
Schedule of Effective Income Tax Rate Reconciliation
The reconciliation of the statutory federal income tax rate to our effective tax rate for each of the years ended December 31, 2023, 2022 and 2021 is as follows:
202320222021
Income Taxes at Federal Statutory Rate$76,332 21.0 %$75,082 21.0 %$44,692 21.0 %
Increases (Decreases) in Tax from:
State Taxes on Income, Net of Federal Tax14,429 4.0 15,049 4.2 9,962 4.7 
Production Tax Credits (PTCs)(17,394)(4.8)(14,985)(4.2)(12,503)(5.9)
Amortization of Excess Deferred Income Taxes(2,205)(0.6)(1,625)(0.5)(4,262)(2.0)
North Dakota Wind Tax Credit Amortization, Net of Federal Tax(586)(0.2)(586)(0.2)(586)(0.3)
Other, Net(1,278)(0.3)416 0.2 (1,251)(0.6)
Income Taxes at Effective Tax Rate$69,298 19.1 %$73,351 20.5 %$36,052 16.9 %
PTCs, North Dakota wind tax credits, and excess deferred income taxes related to the federal tax rate reduction in the 2017 Tax Cuts and Jobs Act are returned to customers as a reduction of the rates they are charged and result in a reduction of operating revenues.
Schedule of Deferred Tax Assets and Liabilities
Deferred tax assets and liabilities were composed of the following on December 31, 2023 and 2022:
(in thousands)20232022
Deferred Tax Assets  
Employee Benefits$39,959 $39,216 
Regulatory Liabilities56,479 57,353 
Tax Credit Carryforwards
21,836 20,209 
Cost of Removal32,993 37,360 
Asset Retirement Obligations
9,494 6,557 
Net Operating Loss Carryforward
2,336 1,853 
Other11,310 5,550 
Total Deferred Tax Assets174,407 168,098 
Deferred Tax Liabilities
Differences Related to Property(347,885)(334,201)
Retirement Benefits Regulatory Asset(22,458)(22,789)
Pension Expense(24,875)(24,269)
Other(16,462)(8,141)
Total Deferred Tax Liabilities(411,680)(389,400)
Deferred Income Taxes$(237,273)$(221,302)
Schedule of Expiration of Operating Loss Carryforwards and Tax Credit Carryforwards
The following is a schedule of tax credits and tax net operating losses available as of December 31, 2023 and the respective periods of expiration:
(in thousands)Amount2024-20292030-20372038-2043
State Net Operating Losses$2,336 $211 $2,125 $— 
State Tax Credits21,836 — — 21,836 
Schedule of Income Tax Contingencies
The following table summarizes the activity for unrecognized tax benefits for the years ended December 31, 2023, 2022 and 2021:
(in thousands)202320222021
Balance on January 1$923 $827 $771 
Increases for tax positions taken during a prior period
596 44 11 
Increases for tax positions taken during the current period163 260 189 
Decreases due to settlements with taxing authorities— — — 
Decreases as a result of a lapse of applicable statutes of limitations(193)(208)(144)
Balance on December 31$1,489 $923 $827 
v3.24.0.1
Commitments and Contingencies (Tables)
 12 Months Ended
Dec. 31, 2023
Commitments and Contingencies Disclosure [Abstract]  
Schedule of Commitments Contractual Obligation Maturities
Our future commitments as of December 31, 2023 were as follows:
(in thousands)Construction Program
and Other Commitments		Capacity and Energy
Requirements		Coal Purchase
Commitments		Land
 Easement
Payments
2024$4,374 $245 $24,691 $1,804 
20254,051 217 24,593 1,840 
20261,377 197 25,374 1,845 
2027594 197 25,786 1,882 
2028550 197 25,344 1,921 
Beyond 20286,165 3,939 359,610 53,107 
Total$17,111 $4,992 $485,398 $62,399 
v3.24.0.1
Accumulated Other Comprehensive Income (Loss) (Tables)
 12 Months Ended
Dec. 31, 2023
Equity [Abstract]  
Schedule of Changes in Accumulated Other Comprehensive Income (Loss)
The following table shows the changes in accumulated other comprehensive Income (loss) for the years ended December 31, 2023, 2022 and 2021:
(in thousands)Pension and Other Postretirement BenefitsNet Unrealized Gain (Losses) on Available-for-Sale SecuritiesTotal
Balance, December 31, 2020
$(8,716)$209 $(8,507)
Other Comprehensive Income (Loss) Before Reclassifications, net of tax
1,638 (132)1,506 
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)541 
(1)
(64)
(2)
477 
Total Other Comprehensive Income (Loss)2,179 (196)1,983 
Balance, December 31, 2021
(6,537)13 (6,524)
Other Comprehensive Income (Loss) Before Reclassifications, net of tax7,331 (433)6,898 
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)540 
(1)
1 
(2)
541 
Total Other Comprehensive Income (Loss)7,871 (432)7,439 
Balance, December 31, 2022
1,334 (419)915 
Other Comprehensive Income Before Reclassifications, net of tax
59 180 239 
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)(18)
(1)
12 
(2)
(6)
Total Other Comprehensive Income
41 192 233 
Balance, December 31, 2023
$1,375 $(227)$1,148 
(1) Included in the computation of net periodic pension and other postretirement benefit costs. See Note 10 for further information.
(2) Included in other income (expense), net on the accompanying consolidated statements of income.
v3.24.0.1
Share-Based Payments (Tables)
 12 Months Ended
Dec. 31, 2023
Share-Based Payment Arrangement [Abstract]  
Summary of Nonvested Restricted Stock Shares Activity
The following is a summary of restricted stock award activity for the year ended December 31, 2023:
SharesWeighted-Average
Grant-Date
Fair Value
Nonvested, Beginning of Year141,551 $49.83 
Granted55,205 68.03 
Vested(45,493)50.02 
Forfeited(2,350)52.02 
Nonvested, End of Year148,913 $56.48 
Schedule of Share-Based Payment Award, Employee Stock Purchase Plan, Valuation Assumptions The grant-date fair value of the TSR component of the stock performance awards granted during the years ended December 31, 2023, 2022 and 2021 was determined using a Monte Carlo fair value simulation model incorporating the following assumptions:
202320222021
Risk-free interest rate4.15 %1.52 %0.18 %
Expected term (in years)3.003.003.00
Expected volatility34.00 %32.00 %32.00 %
Dividend yield2.50 %2.90 %3.60 %
Schedule of Share-based Compensation Arrangements by Share-based Payment Award
The following is a summary of stock performance award activity for the year ended December 31, 2023 (share amounts reflect awards at target):
 SharesWeighted-Average
Grant-Date
Fair Value
Nonvested, Beginning of Year189,800 $45.95 
Granted59,400 61.97 
Vested(55,000)47.79 
Forfeited— — 
Nonvested, End of Year194,200 $50.33 
v3.24.0.1
Earnings Per Share (Tables)
 12 Months Ended
Dec. 31, 2023
Earnings Per Share [Abstract]  
Schedule of Earnings Per Share, Basic and Diluted
The following includes the computation of the denominator for basic and diluted weighted-average shares outstanding for the years ended December 31, 2023, 2022 and 2021:
(in thousands)202320222021
Weighted Average Common Shares Outstanding – Basic41,668 41,586 41,491 
Effect of Dilutive Securities:
Stock Performance Awards269 248 226 
Restricted Stock Awards100 95 87 
Employee Stock Purchase Plan Shares and Other2 2 14 
Dilutive Effect of Potential Common Shares371 345 327 
Weighted Average Common Shares Outstanding – Diluted42,039 41,931 41,818 
v3.24.0.1
Fair Value Measurements (Tables)
 12 Months Ended
Dec. 31, 2023
Fair Value Disclosures [Abstract]  
Schedule of Fair Value, Assets Measured on Recurring Basis
The following tables present our assets measured at fair value on a recurring basis as of December 31, 2023 and 2022 classified by the input method used to measure fair value:
Level 1Level 2Level 3
December 31, 2023
Assets
Investments:
Money Market Funds$3,125 $— $— 
Mutual Funds7,771 — — 
Corporate Debt Securities— 1,579 — 
Government Debt Securities
— 7,724 — 
Total Assets10,896 9,303 — 
Liabilities
Derivative Instruments— 4,210 — 
Total Liabilities$— $4,210 $— 
December 31, 2022
Assets
Investments:
Money Market Funds$1,560 $— $— 
Mutual Funds5,503 — — 
Corporate Debt Securities— 1,434 — 
Government Debt Securities
— 7,327 — 
Total Assets$7,063 $8,761 $— 
Liabilities
Derivative Instruments— 7,130 — 
Total Liabilities
$— $7,130 $— 
Schedule of Fair Value of Assets and Liabilities The following reflects the carrying value and estimated fair value of these assets and liabilities as of December 31, 2023 and 2022:
 December 31, 2023December 31, 2022
(in thousands)Carrying
Amount		Fair ValueCarrying
Amount		Fair Value
Assets:
Cash and Cash Equivalents$230,373 $230,373 $118,996 $118,996 
Total230,373 230,373 118,996 118,996 
Liabilities:
Short-Term Debt81,422 81,422 8,204 8,204 
Long-Term Debt824,059 710,839 823,821 681,615 
Total$905,481 $792,261 $832,025 $689,819 
v3.24.0.1
Schedule I - Condensed Financial Information of Registrant (Tables)
 12 Months Ended
Dec. 31, 2023
Condensed Financial Information Disclosure [Abstract]  
Condensed Balance Sheet
SCHEDULE I - CONDENSED FINANCIAL INFORMATION OF REGISTRANT
OTTER TAIL CORPORATION (PARENT COMPANY)
CONDENSED BALANCE SHEETS
December 31,
(in thousands)20232022
Assets
Current Assets
Cash and Cash Equivalents$228,137 $119,246 
Accounts Receivable from Subsidiaries2,555 3,278 
Interest Receivable from Subsidiaries117 117 
Other977 1,045 
Total Current Assets231,786 123,686 
Investments in Subsidiaries1,725,584 1,463,998 
Notes Receivable from Subsidiaries78,900 78,900 
Deferred Income Taxes65,244 64,802 
Other Assets50,795 43,779 
Total Assets$2,152,309 $1,775,165 
Liabilities and Stockholders' Equity
Current Liabilities
Accounts Payable to Subsidiaries$7 $7 
Notes Payable to Subsidiaries568,672 420,363 
Other15,320 15,994 
Total Current Liabilities583,999 436,364 
Other Noncurrent Liabilities45,455 41,686 
Commitments and Contingencies
Capitalization
Long-Term Debt
79,849 79,798 
Common Stockholders' Equity1,443,006 1,217,317 
Total Capitalization1,522,855 1,297,115 
Total Liabilities and Stockholders' Equity$2,152,309 $1,775,165 
Condensed Income Statement
OTTER TAIL CORPORATION (PARENT COMPANY)
CONDENSED STATEMENTS OF INCOME
Years Ended December 31,
(in thousands)202320222021
Income
Equity Income in Earnings of Subsidiaries$294,467 $296,833 $188,375 
Interest Income from Subsidiaries2,898 3,382 2,826 
Other Income10,496 466 1,290 
Total Income307,861 300,681 192,491 
Expense
Nonelectric Selling, General, and Administrative Expenses12,816 17,269 14,825 
Interest Expense
3,813 4,066 4,727 
Interest Expense from Subsidiaries
6 5 3 
Nonservice Cost Components of Postretirement Benefits1,063 1,023 1,097 
Total Expense17,698 22,363 20,652 
Income Before Income Taxes290,163 278,318 171,839 
Income Tax Benefit4,028 5,866 4,930 
Net Income$294,191 $284,184 $176,769 
Condensed Cash Flow Statement
OTTER TAIL CORPORATION (PARENT COMPANY)
CONDENSED STATEMENTS OF CASH FLOWS
Years Ended December 31,
(in thousands)202320222021
Cash Flows from Operating Activities
Net Cash Provided by Operating Activities$77,139 $28,807 $60,695 
Cash Flows from Investing Activities
Investment in Subsidiaries(40,000)(50,000)— 
Debt Repaid by Subsidiaries— — 169 
Other, net(68)(1,695)(884)
Net Cash Used in Investing Activities(40,068)(51,695)(715)
Cash Flows from Financing Activities
Net (Repayments) Borrowings on Short-Term Debt— (22,637)(42,529)
Borrowings from Subsidiaries148,308 236,926 49,085 
Proceeds from Issuance of Common Stock— — 696 
Payments for Shares Withheld for Employee Tax Obligations(3,088)(2,942)(1,507)
Payments for Retirement of Long-Term Debt— — (169)
Dividends Paid(73,061)(68,755)(64,864)
Other, net(339)(461)(689)
Net Cash Provided by (Used in) Financing Activities71,820 142,131 (59,977)
Net Change in Cash and Cash Equivalents108,891 119,243 3 
Cash and Cash Equivalents at Beginning of Period119,246 3 — 
Cash and Cash Equivalents at End of Period$228,137 $119,246 $3 
Schedule of Related Party Transactions
Outstanding receivables from and payables to OTC's subsidiaries as of December 31, 2023 and 2022 are as follows:
(in thousands)Accounts
Receivable		Interest
Receivable		Long-Term
Notes
Receivable		Accounts
Payable		Current
Notes
Payable
December 31, 2023
Otter Tail Power Company$2,415 $— $— $7 $— 
Northern Pipe Products, Inc.— 7 5,000 — 56,917 
Vinyltech Corporation14 17 11,500 — 98,016 
BTD Manufacturing, Inc.— 78 52,000 — 6,291 
T.O. Plastics, Inc.36 15 10,400 — 980 
Varistar Corporation— — — — 406,468 
Otter Tail Assurance Limited90 — — — — 
 $2,555 $117 $78,900 $7 $568,672 
December 31, 2022
Otter Tail Power Company$3,016 $— $— $7 $— 
Northern Pipe Products, Inc.— 7 5,000 — 77,182 
Vinyltech Corporation— 18 11,500 — 90,425 
BTD Manufacturing, Inc.— 77 52,000 — 693 
T.O. Plastics, Inc.20 15 10,400 — 5,855 
Varistar Corporation— — — — 246,208 
Otter Tail Assurance Limited242 — — — — 
$3,278 $117 $78,900 $7 $420,363 
Cash Dividends Paid to Parent by Subsidiaries
Dividends paid to OTC (the Parent) from its subsidiaries were as follows:
(in thousands)202320222021
Cash Dividends Paid to Parent by Subsidiaries$72,982 $68,680 $64,790 
v3.24.0.1
Summary of Significant Accounting Policies - Narrative (Details)
$ in Thousands
 12 Months Ended
Dec. 31, 2023
USD ($)
segment
foundation
plant
reportingUnit
plan
line
Dec. 31, 2022
USD ($)
foundation
Dec. 31, 2021
USD ($)
foundation
Property, Plant and Equipment [Line Items]      
Number of operating segments | segment 3    
Investments gain (loss) $ 7,222 $ (3,296) $ 4,524
Allowance for equity funds used during construction   1,700 800
Number of jointly owned electric generation plants | plant 2    
Number of jointly owned major transmission lines | line 5    
Number of reporting units | reportingUnit 3    
Amortization period 10 years    
Amortization expense $ 1,300 1,400 500
Number of plans offered | plan 2    
Deferred compensation liability, company contributions $ 24,600 20,600  
Deferred compensation arrangement, contributions by employer 1,200 900 1,100
Deferred compensation liability, gain (loss) due to payment obligations (3,300) 3,100 $ (2,200)
Contribution Obligation | Related Party      
Property, Plant and Equipment [Line Items]      
Related party transaction, amounts of transaction $ 5,500 $ 4,300  
Number of foundations transacting with | foundation 2 2 2
Contribution Obligation Paid | Related Party      
Property, Plant and Equipment [Line Items]      
Related party transaction, amounts of transaction $ 4,300 $ 4,500 $ 3,800
Number of foundations transacting with | foundation 2 2 2
OTP | Coyote Creek Mining Company, L.L.C. (CCMC) | Lignite Sales Agreement      
Property, Plant and Equipment [Line Items]      
Variable interest entity, reporting entity involvement, maximum loss exposure, amount $ 40,000    
Variable interest entity, reporting entity involvement, maximum loss exposure (as a percent) 35.00%    
Minimum      
Property, Plant and Equipment [Line Items]      
Intangible asset, useful life 15 years    
Operating lease, term 1 year    
Maximum      
Property, Plant and Equipment [Line Items]      
Intangible asset, useful life 20 years    
Operating lease, term 10 years    
Electric Plant in Service      
Property, Plant and Equipment [Line Items]      
Interest costs capitalized $ 1,900 $ 900 $ 600
v3.24.0.1
Summary of Significant Accounting Policies - Summary of Inventories (Details) - USD ($)
$ in Thousands
Dec. 31, 2023
Dec. 31, 2022
Accounting Policies [Abstract]    
Finished Goods $ 47,614 $ 43,812
Work in Process 26,354 31,766
Raw Material, Fuel and Supplies 75,733 70,374
Total Inventories $ 149,701 $ 145,952
v3.24.0.1
Summary of Significant Accounting Policies - Summary of Investments (Details) - USD ($)
$ in Thousands
Dec. 31, 2023
Dec. 31, 2022
Accounting Policies [Abstract]    
Corporate-Owned Life Insurance Policies $ 42,287 $ 38,991
Corporate and Government Debt Securities 9,303 8,761
Mutual Funds 7,771 5,503
Money Market Funds 3,125 1,560
Other Investments 30 30
Total Investments $ 62,516 $ 54,845
v3.24.0.1
Summary of Significant Accounting Policies - Summary of Estimated Service Lives (Details)
 12 Months Ended
Dec. 31, 2023
Minimum | Equipment | Electric Plant in Service  
Public Utility, Property, Plant and Equipment [Line Items]  
Production, useful life 21 years
Transmission, useful life 51 years
Distribution, useful life 10 years
General, useful life 5 years
Minimum | Equipment | Nonelectric Property, Plant and Equipment  
Public Utility, Property, Plant and Equipment [Line Items]  
Useful life 2 years
Minimum | Buildings and Leasehold Improvements | Nonelectric Property, Plant and Equipment  
Public Utility, Property, Plant and Equipment [Line Items]  
Useful life 2 years
Maximum | Equipment | Electric Plant in Service  
Public Utility, Property, Plant and Equipment [Line Items]  
Production, useful life 114 years
Transmission, useful life 75 years
Distribution, useful life 70 years
General, useful life 56 years
Maximum | Equipment | Nonelectric Property, Plant and Equipment  
Public Utility, Property, Plant and Equipment [Line Items]  
Useful life 20 years
Maximum | Buildings and Leasehold Improvements | Nonelectric Property, Plant and Equipment  
Public Utility, Property, Plant and Equipment [Line Items]  
Useful life 40 years
v3.24.0.1
Summary of Significant Accounting Policies - Summary of Capitalized Cost and Related Accumulated Amortization (Details) - USD ($)
$ in Thousands
Dec. 31, 2023
Dec. 31, 2022
Accounting Policies [Abstract]    
Cloud Computing Costs $ 12,782 $ 9,024
Accumulated Amortization (1,505) (897)
Cloud Computing Costs, net $ 11,277 $ 8,127
v3.24.0.1
Segment Information - Narrative (Details)
 12 Months Ended
Dec. 31, 2023
segment
Segment Reporting [Abstract]  
Number of operating segments 3
Number of reportable segments 3
v3.24.0.1
Segment Information - Summary of Business Segments (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Segment Reporting Information [Line Items]      
Operating Revenue $ 1,349,166 $ 1,460,209 $ 1,196,844
Depreciation and Amortization 97,954 92,597 91,358
Operating Income (Loss) 377,919 390,439 249,708
Interest Expense 37,677 36,016 37,771
Income Tax Expense (Benefit) 69,298 73,351 36,052
Net Income (Loss) 294,191 284,184 176,769
Capital Expenditures 287,134 171,134 171,829
Identifiable Assets 3,242,568 2,901,661  
Corporate      
Segment Reporting Information [Line Items]      
Depreciation and Amortization 102 140 225
Operating Income (Loss) (12,144) (16,342) (14,130)
Interest Expense 916 685 1,902
Income Tax Expense (Benefit) (3,806) (5,723) (4,689)
Net Income (Loss) 565 (12,114) (10,698)
Capital Expenditures 126 66 68
Identifiable Assets 293,215 177,513  
Electric      
Segment Reporting Information [Line Items]      
Operating Revenue 528,359 549,699 480,321
Electric | Operating Segments      
Segment Reporting Information [Line Items]      
Operating Revenue 528,359 549,699 480,321
Depreciation and Amortization 75,330 72,050 71,343
Operating Income (Loss) 106,521 113,138 106,964
Interest Expense 33,864 31,950 33,043
Income Tax Expense (Benefit) 1,648 5,065 1,663
Net Income (Loss) 84,424 79,974 72,458
Capital Expenditures 240,695 147,869 140,031
Identifiable Assets 2,533,831 2,351,961  
Manufacturing      
Segment Reporting Information [Line Items]      
Operating Revenue 402,781 397,983 336,294
Manufacturing | Operating Segments      
Segment Reporting Information [Line Items]      
Operating Revenue 402,781 397,983 336,294
Depreciation and Amortization 18,495 16,202 15,436
Operating Income (Loss) 29,140 29,065 24,114
Interest Expense 2,295 2,796 2,239
Income Tax Expense (Benefit) 5,390 5,321 4,704
Net Income (Loss) 21,454 20,950 17,186
Capital Expenditures 23,284 17,954 20,690
Identifiable Assets 251,343 245,869  
Plastics      
Segment Reporting Information [Line Items]      
Operating Revenue 418,026 512,527 380,229
Plastics | Operating Segments      
Segment Reporting Information [Line Items]      
Operating Revenue 418,026 512,527 380,229
Depreciation and Amortization 4,027 4,205 4,354
Operating Income (Loss) 254,402 264,578 132,760
Interest Expense 602 585 587
Income Tax Expense (Benefit) 66,066 68,688 34,374
Net Income (Loss) 187,748 195,374 97,823
Capital Expenditures 23,029 5,245 $ 11,040
Identifiable Assets $ 164,179 $ 126,318  
v3.24.0.1
Revenue (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Disaggregation of Revenue [Line Items]      
Total Operating Revenues $ 1,349,166 $ 1,460,209 $ 1,196,844
Total Operating Revenues from Contracts with Customers 1,353,476 1,469,475 1,197,635
Electric      
Disaggregation of Revenue [Line Items]      
Total Operating Revenues 528,359 549,699 480,321
Electric Segment - ARP Revenues (4,310) (9,266) (791)
Manufacturing      
Disaggregation of Revenue [Line Items]      
Total Operating Revenues 402,781 397,983 336,294
Plastics      
Disaggregation of Revenue [Line Items]      
Total Operating Revenues 418,026 512,527 380,229
Total Retail | Electric      
Disaggregation of Revenue [Line Items]      
Total Operating Revenues 455,840 470,300 405,484
Retail: Residential | Electric      
Disaggregation of Revenue [Line Items]      
Total Operating Revenues 135,570 143,888 135,361
Retail: Commercial and Industrial | Electric      
Disaggregation of Revenue [Line Items]      
Total Operating Revenues 312,551 318,494 262,408
Retail: Other | Electric      
Disaggregation of Revenue [Line Items]      
Total Operating Revenues 7,719 7,918 7,715
Transmission | Electric      
Disaggregation of Revenue [Line Items]      
Total Operating Revenues 52,555 52,213 48,835
Wholesale | Electric      
Disaggregation of Revenue [Line Items]      
Total Operating Revenues 12,459 18,539 17,936
Other | Electric      
Disaggregation of Revenue [Line Items]      
Total Operating Revenues 7,505 8,647 8,066
Metal Parts and Tooling | Manufacturing      
Disaggregation of Revenue [Line Items]      
Total Operating Revenues 351,267 338,865 283,527
Plastic Products and Tooling | Manufacturing      
Disaggregation of Revenue [Line Items]      
Total Operating Revenues 41,395 49,080 40,231
Scrap Metal | Manufacturing      
Disaggregation of Revenue [Line Items]      
Total Operating Revenues $ 10,119 $ 10,038 $ 12,536
v3.24.0.1
Receivables - Summary of Receivables (Details) - USD ($)
$ in Thousands
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Receivables [Abstract]      
Trade $ 129,257 $ 112,126  
Other 9,084 9,983  
Unbilled Receivables 21,324 23,932  
Total Receivables 159,665 146,041  
Less Allowance for Credit Losses 2,522 1,648 $ 1,836
Receivables, net of allowance for credit losses $ 157,143 $ 144,393  
v3.24.0.1
Receivables - Summary of Allowance for Credit Loss (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Accounts Receivable, Allowance for Credit Loss [Roll Forward]    
Beginning Balance $ 1,648 $ 1,836
Additions Charged to Expense 2,014 909
Reductions for Amounts Written Off, Net of Recoveries (1,140) (1,097)
Ending Balance $ 2,522 $ 1,648
v3.24.0.1
Regulatory Matters - Summary of Regulatory Assets and Liabilities (Details) - USD ($)
$ in Thousands
Dec. 31, 2023
Dec. 31, 2022
Schedule of Regulatory Assets and Liabilities [Line Items]    
Regulatory assets - current $ 16,127 $ 24,999
Regulatory assets, long-term 95,715 94,655
Regulatory liabilities, current 25,408 17,300
Regulatory liabilities, long -term 276,547 244,497
Deferred Income Taxes    
Schedule of Regulatory Assets and Liabilities [Line Items]    
Regulatory liabilities, current 0 0
Regulatory liabilities, long -term 136,022 131,480
Plant Removal Obligations    
Schedule of Regulatory Assets and Liabilities [Line Items]    
Regulatory liabilities, current 0 8,509
Regulatory liabilities, long -term 117,030 105,733
Fuel Clause Adjustments    
Schedule of Regulatory Assets and Liabilities [Line Items]    
Regulatory liabilities, current 11,350 365
Regulatory liabilities, long -term $ 0 0
Regulatory liabilities - remaining recovery/refund period 1 year  
Alternative Revenue Program Riders    
Schedule of Regulatory Assets and Liabilities [Line Items]    
Regulatory liabilities, current $ 6,885 2,504
Regulatory liabilities, long -term $ 0 0
Regulatory liabilities - remaining recovery/refund period 1 year  
North Dakota PTC Refunds    
Schedule of Regulatory Assets and Liabilities [Line Items]    
Regulatory liabilities, current $ 0 0
Regulatory liabilities, long -term 12,011 7,136
Pension and Other Postretirement Benefit Plans    
Schedule of Regulatory Assets and Liabilities [Line Items]    
Regulatory liabilities, current 6,138 5,589
Regulatory liabilities, long -term 11,307 0
Other    
Schedule of Regulatory Assets and Liabilities [Line Items]    
Regulatory liabilities, current 1,035 333
Regulatory liabilities, long -term 177 148
Pension and Other Postretirement Benefit Plans    
Schedule of Regulatory Assets and Liabilities [Line Items]    
Regulatory assets - current 154 0
Regulatory assets, long-term 86,134 88,354
Alternative Revenue Program Riders    
Schedule of Regulatory Assets and Liabilities [Line Items]    
Regulatory assets - current 3,719 5,679
Regulatory assets, long-term $ 158 2,508
Regulatory assets - Remaining recovery/refund period 2 years  
Asset Retirement Obligations    
Schedule of Regulatory Assets and Liabilities [Line Items]    
Regulatory assets - current $ 0 0
Regulatory assets, long-term 87 1,467
Deferred Income Taxes    
Schedule of Regulatory Assets and Liabilities [Line Items]    
Regulatory assets - current 0 0
Regulatory assets, long-term 6,940 0
Fuel Clause Adjustments    
Schedule of Regulatory Assets and Liabilities [Line Items]    
Regulatory assets - current 7,294 10,893
Regulatory assets, long-term $ 0 0
Regulatory assets - Remaining recovery/refund period 1 year  
Derivative Instruments    
Schedule of Regulatory Assets and Liabilities [Line Items]    
Regulatory assets - current $ 4,210 7,130
Regulatory assets, long-term $ 0 0
Regulatory assets - Remaining recovery/refund period 1 year  
Other    
Schedule of Regulatory Assets and Liabilities [Line Items]    
Regulatory assets - current $ 750 1,297
Regulatory assets, long-term $ 2,396 $ 2,326
v3.24.0.1
Regulatory Matters - Narrative (Details) - North Dakota Rate Case - NDPSC
$ in Millions
Nov. 02, 2023
USD ($)
Schedule of Regulatory Assets and Liabilities [Line Items]  
Requested rate increase, amount $ 17.4
Requested rate increase, percent (as a percent) 8.40%
Requested return on base rate, percent (as a percent) 7.85%
Requested equity ratio, percent (as a percent) 10.60%
Requested return on equity, percent (as a percent) 53.50%
Revenue, interim rate increase, amount $ 12.4
Revenue, interim rate increase, percentage (as a percent) 6.00%
v3.24.0.1
Property, Plant and Equipment - Summary of Property, Plant and Equipment (Details) - USD ($)
$ in Thousands
Dec. 31, 2023
Dec. 31, 2022
Property, Plant and Equipment [Line Items]    
Property, Plant and Equipment, net of accumulated depreciation $ 2,418,375 $ 2,212,717
Electric Plant in Service    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 3,127,093 2,958,311
Less Accumulated Depreciation and Amortization 851,148 859,988
Property, Plant and Equipment, net of accumulated depreciation 2,275,945 2,098,323
Nonelectric Property, Plant and Equipment    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 349,986 309,098
Less Accumulated Depreciation and Amortization 207,556 194,704
Property, Plant and Equipment, net of accumulated depreciation 142,430 114,394
Production | Electric Plant in Service    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 1,412,826 1,343,097
Transmission | Electric Plant in Service    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 777,613 756,848
Distribution | Electric Plant in Service    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 654,704 612,716
General | Electric Plant in Service    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 144,738 131,718
Electric Plant in Service | Electric Plant in Service    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 2,989,881 2,844,379
Construction Work in Progress | Electric Plant in Service    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 137,212 113,932
Construction Work in Progress | Nonelectric Property, Plant and Equipment    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 38,062 15,170
Equipment | Nonelectric Property, Plant and Equipment    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 233,571 218,770
Buildings and Leasehold Improvements | Nonelectric Property, Plant and Equipment    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 64,753 61,506
Land | Nonelectric Property, Plant and Equipment    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 13,600 13,652
Nonelectric Property, Plant and Equipment | Nonelectric Property, Plant and Equipment    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross $ 311,924 $ 293,928
v3.24.0.1
Property, Plant and Equipment - Narrative (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Property, Plant and Equipment [Abstract]      
Depreciation expense $ 90.8 $ 84.4 $ 85.8
v3.24.0.1
Property, Plant and Equipment - Summary of Jointly Owned Utility Plants (Details) - USD ($)
$ in Thousands
Dec. 31, 2023
Dec. 31, 2022
Big Stone Plant    
Jointly Owned Utility Plant Interests [Line Items]    
Electric Plant in Service $ 341,683 $ 338,411
Construction Work in Progress 820 557
Accumulated Depreciation (126,904) (118,044)
Net Plant $ 215,599 $ 220,924
Big Stone Plant | OTP    
Jointly Owned Utility Plant Interests [Line Items]    
Ownership Percentage 53.90% 53.90%
Coyote Station    
Jointly Owned Utility Plant Interests [Line Items]    
Electric Plant in Service $ 188,656 $ 183,461
Construction Work in Progress 104 2,315
Accumulated Depreciation (115,306) (111,666)
Net Plant $ 73,454 $ 74,110
Coyote Station | OTP    
Jointly Owned Utility Plant Interests [Line Items]    
Ownership Percentage 35.00% 35.00%
Big Stone South–Ellendale 345 kV line    
Jointly Owned Utility Plant Interests [Line Items]    
Electric Plant in Service $ 106,185 $ 106,185
Construction Work in Progress 0 0
Accumulated Depreciation (7,181) (5,587)
Net Plant $ 99,004 $ 100,598
Big Stone South–Ellendale 345 kV line | OTP    
Jointly Owned Utility Plant Interests [Line Items]    
Ownership Percentage 50.00% 50.00%
Fargo–Monticello 345 kV line    
Jointly Owned Utility Plant Interests [Line Items]    
Electric Plant in Service $ 78,184 $ 78,184
Construction Work in Progress 0 0
Accumulated Depreciation (11,238) (10,095)
Net Plant $ 66,946 $ 68,089
Fargo–Monticello 345 kV line | OTP    
Jointly Owned Utility Plant Interests [Line Items]    
Ownership Percentage 14.20% 14.20%
Big Stone South–Brookings 345 kV line    
Jointly Owned Utility Plant Interests [Line Items]    
Electric Plant in Service $ 53,170 $ 53,041
Construction Work in Progress 0 0
Accumulated Depreciation (5,207) (4,406)
Net Plant $ 47,963 $ 48,635
Big Stone South–Brookings 345 kV line | OTP    
Jointly Owned Utility Plant Interests [Line Items]    
Ownership Percentage 50.00% 50.00%
Brookings–Southeast Twin Cities 345 kV line    
Jointly Owned Utility Plant Interests [Line Items]    
Electric Plant in Service $ 26,409 $ 26,291
Construction Work in Progress 83 0
Accumulated Depreciation (3,617) (3,211)
Net Plant $ 22,875 $ 23,080
Brookings–Southeast Twin Cities 345 kV line | OTP    
Jointly Owned Utility Plant Interests [Line Items]    
Ownership Percentage 4.80% 4.80%
Bemidji–Grand Rapids 230 kV line    
Jointly Owned Utility Plant Interests [Line Items]    
Electric Plant in Service $ 16,331 $ 16,331
Construction Work in Progress 0 0
Accumulated Depreciation (3,568) (3,318)
Net Plant $ 12,763 $ 13,013
Bemidji–Grand Rapids 230 kV line | OTP    
Jointly Owned Utility Plant Interests [Line Items]    
Ownership Percentage 14.80% 14.80%
Jamestown– Ellendale 345 kV line    
Jointly Owned Utility Plant Interests [Line Items]    
Electric Plant in Service $ 0  
Construction Work in Progress 1,121  
Accumulated Depreciation 0  
Net Plant $ 1,121  
Jamestown– Ellendale 345 kV line | OTP    
Jointly Owned Utility Plant Interests [Line Items]    
Ownership Percentage 50.00%  
Big Stone South–Alexandria 345 kV line    
Jointly Owned Utility Plant Interests [Line Items]    
Electric Plant in Service $ 0  
Construction Work in Progress 555  
Accumulated Depreciation 0  
Net Plant $ 555  
Big Stone South–Alexandria 345 kV line | OTP    
Jointly Owned Utility Plant Interests [Line Items]    
Ownership Percentage 40.00%  
Alexandria–Big Oaks 345 kV line    
Jointly Owned Utility Plant Interests [Line Items]    
Electric Plant in Service $ 0  
Construction Work in Progress 343  
Accumulated Depreciation 0  
Net Plant $ 343  
Alexandria–Big Oaks 345 kV line | OTP    
Jointly Owned Utility Plant Interests [Line Items]    
Ownership Percentage 14.20%  
v3.24.0.1
Intangible Assets - Summary of Goodwill by Segment (Details) - USD ($)
$ in Thousands
Dec. 31, 2023
Dec. 31, 2022
Goodwill [Line Items]    
Goodwill $ 37,572 $ 37,572
Manufacturing    
Goodwill [Line Items]    
Goodwill 18,270 18,270
Plastics    
Goodwill [Line Items]    
Goodwill $ 19,302 $ 19,302
v3.24.0.1
Intangible Assets - Summary of Components of Intangible Assets (Details) - USD ($)
$ in Thousands
Dec. 31, 2023
Dec. 31, 2022
Finite-Lived Intangible Assets [Line Items]    
Gross Amount $ 22,517 $ 22,517
Accumulated Amortization 15,674 14,574
Net Carrying Amount 6,843 7,943
Customer Relationships    
Finite-Lived Intangible Assets [Line Items]    
Gross Amount 22,491 22,491
Accumulated Amortization 15,667 14,568
Net Carrying Amount 6,824 7,923
Other    
Finite-Lived Intangible Assets [Line Items]    
Gross Amount 26 26
Accumulated Amortization 7 6
Net Carrying Amount $ 19 $ 20
v3.24.0.1
Intangible Assets - Narrative (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Goodwill and Intangible Assets Disclosure [Abstract]      
Amortization expense $ 1.1 $ 1.1 $ 1.1
v3.24.0.1
Intangible Assets - Summary of Intangible Assets Future Amortization Expenses (Details)
$ in Thousands
Dec. 31, 2023
USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]  
2024 $ 1,100
2025 1,100
2026 1,092
2027 1,090
2028 $ 554
v3.24.0.1
Leases - Summary of Lease Costs (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Lease Cost      
Operating Lease Cost $ 6,309 $ 5,606 $ 5,298
Variable Lease Cost 1,433 1,386 1,020
Short-Term Lease Cost 2,525 1,517 1,465
Total Lease Cost 10,267 8,509 7,783
Lease Cash Flows      
Operating Cash Flows from Operating Leases $ 6,424 $ 5,592 $ 5,642
v3.24.0.1
Leases - Summary of Supplemental Balance Sheet (Details) - USD ($)
$ in Thousands
Dec. 31, 2023
Dec. 31, 2022
Leases [Abstract]    
Right of Use Lease Asset $ 16,788 $ 18,610
Lease Liabilities    
Current 5,756 5,071
Long-Term 11,258 13,876
Total Lease Liabilities $ 17,014 $ 18,947
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List] Other Noncurrent Assets Other Noncurrent Assets
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List] Other Current Liabilities Other Current Liabilities
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List] Other Noncurrent Liabilities Other Noncurrent Liabilities
v3.24.0.1
Leases - Narrative (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Leases [Abstract]    
Right-of-use asset obtained in exchange for operating lease liability $ 3.6 $ 3.7
v3.24.0.1
Leases - Summary of Operating Lease Liability Maturities (Details) - USD ($)
$ in Thousands
Dec. 31, 2023
Dec. 31, 2022
Leases [Abstract]    
2024 $ 6,473  
2025 5,357  
2026 3,068  
2027 2,196  
2028 1,059  
Thereafter 368  
Total Lease Payments 18,521  
Less: Interest 1,507  
Present Value of Lease Liabilities $ 17,014 $ 18,947
v3.24.0.1
Leases - Summary of Weighted-Average Remaining Lease Term and Discount Rate (Details)
Dec. 31, 2023
Dec. 31, 2022
Leases [Abstract]    
Weighted-Average Remaining Lease Term (in years) 3 years 4 months 24 days 4 years 2 months 12 days
Weighted-Average Discount Rate 5.40% 4.73%
v3.24.0.1
Short-Term and Long-Term Borrowings - Summary of Debt (Details) - USD ($)
$ in Thousands
Dec. 31, 2023
Dec. 31, 2022
Debt Instrument [Line Items]    
Short-Term Debt $ 81,422 $ 8,204
Current Maturities of Long-Term Debt 0 0
Long-Term Debt 824,059 823,821
Total 905,481 832,025
OTC    
Debt Instrument [Line Items]    
Short-Term Debt 0 0
Current Maturities of Long-Term Debt 0 0
Long-Term Debt 79,849 79,798
Total 79,849 79,798
OTP    
Debt Instrument [Line Items]    
Short-Term Debt 81,422 8,204
Current Maturities of Long-Term Debt 0 0
Long-Term Debt 744,210 744,023
Total $ 825,632 $ 752,227
v3.24.0.1
Short-Term and Long-Term Borrowings - Summary of Lines of Credit (Details) - USD ($)
Dec. 31, 2023
Dec. 31, 2022
Line of Credit Facility [Line Items]    
Line Limit $ 340,000,000  
Amount Outstanding 81,422,000 $ 8,204,000
Letters of Credit 9,132,000  
Amount Available 249,446,000 322,223,000
OTC Credit Agreement    
Line of Credit Facility [Line Items]    
Line Limit 170,000,000  
Amount Outstanding 0  
Letters of Credit 0  
Amount Available 170,000,000 170,000,000
OTP Credit Agreement    
Line of Credit Facility [Line Items]    
Line Limit 170,000,000  
Amount Outstanding 81,422,000  
Letters of Credit 9,132,000  
Amount Available $ 79,446,000 $ 152,223,000
v3.24.0.1
Short-Term and Long-Term Borrowings - Narrative (Details) - USD ($)
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Debt Instrument [Line Items]    
Line of credit facility, maximum borrowing capacity $ 340,000,000  
Debt, weighted average interest rate (as a percent) 6.70% 5.61%
Debt instrument, redemption price, percentage 100.00%  
Minimum    
Debt Instrument [Line Items]    
Interest and dividend coverage ratio 1.50  
Minimum | Benchmark rate    
Debt Instrument [Line Items]    
Debt instrument, basis spread on variable rate (as a percent) 0.00%  
Maximum    
Debt Instrument [Line Items]    
Debt to total capitalization ratio 60.00%  
Maximum | Benchmark rate    
Debt Instrument [Line Items]    
Debt instrument, basis spread on variable rate (as a percent) 2.00%  
OTP Credit Agreement    
Debt Instrument [Line Items]    
Line of credit facility, maximum borrowing capacity $ 170,000,000  
Line of credit facility, increased current borrowing capacity, accordion provision 250,000,000  
OTC Credit Agreement    
Debt Instrument [Line Items]    
Line of credit facility, maximum borrowing capacity 170,000,000  
Line of credit facility, increased current borrowing capacity, accordion provision 290,000,000  
Revolving Credit Facility | OTP Credit Agreement    
Debt Instrument [Line Items]    
Line of credit facility, maximum borrowing capacity 170,000,000  
Revolving Credit Facility | OTC Credit Agreement    
Debt Instrument [Line Items]    
Line of credit facility, maximum borrowing capacity 170,000,000  
Letter of Credit | OTP Credit Agreement    
Debt Instrument [Line Items]    
Line of credit facility, maximum borrowing capacity 50,000,000  
Letter of Credit | OTC Credit Agreement    
Debt Instrument [Line Items]    
Line of credit facility, maximum borrowing capacity $ 40,000,000  
v3.24.0.1
Short-Term and Long-Term Borrowings - Summary of Outstanding Long-term Debt (Details) - USD ($)
$ in Thousands
Dec. 31, 2023
Dec. 31, 2022
Debt Instrument [Line Items]    
Long-term debt $ 827,000 $ 827,000
Unamortized Long-Term Debt Issuance Costs 2,941 3,179
Total Long-Term Debt Net of Unamortized Debt Issuance Costs $ 824,059 823,821
Guaranteed Senior Notes    
Debt Instrument [Line Items]    
Rate (as a percent) 3.55%  
Long-term debt $ 80,000 80,000
Series 2007C Senior Unsecured Notes    
Debt Instrument [Line Items]    
Rate (as a percent) 6.37%  
Long-term debt $ 42,000 42,000
Series 2013A Senior Unsecured Notes    
Debt Instrument [Line Items]    
Rate (as a percent) 4.68%  
Long-term debt $ 60,000 60,000
Series 2019A Senior Unsecured Notes    
Debt Instrument [Line Items]    
Rate (as a percent) 3.07%  
Long-term debt $ 10,000 10,000
Series 2020A Senior Unsecured Notes    
Debt Instrument [Line Items]    
Rate (as a percent) 3.22%  
Long-term debt $ 10,000 10,000
Series 2020B Senior Unsecured Notes    
Debt Instrument [Line Items]    
Rate (as a percent) 3.22%  
Long-term debt $ 40,000 40,000
Series 2021A Senior Unsecured Notes    
Debt Instrument [Line Items]    
Rate (as a percent) 2.74%  
Long-term debt $ 40,000 40,000
Series 2007D Senior Unsecured Notes    
Debt Instrument [Line Items]    
Rate (as a percent) 6.47%  
Long-term debt $ 50,000 50,000
Series 2019B Senior Unsecured Notes    
Debt Instrument [Line Items]    
Rate (as a percent) 3.52%  
Long-term debt $ 26,000 26,000
Series 2020C Senior Unsecured Notes    
Debt Instrument [Line Items]    
Rate (as a percent) 3.62%  
Long-term debt $ 10,000 10,000
Series 2013B Senior Unsecured Notes    
Debt Instrument [Line Items]    
Rate (as a percent) 5.47%  
Long-term debt $ 90,000 90,000
Series 2018A Senior Unsecured Notes    
Debt Instrument [Line Items]    
Rate (as a percent) 4.07%  
Long-term debt $ 100,000 100,000
Series 2019C Senior Unsecured Notes    
Debt Instrument [Line Items]    
Rate (as a percent) 3.82%  
Long-term debt $ 64,000 64,000
Series 2020D Senior Unsecured Notes    
Debt Instrument [Line Items]    
Rate (as a percent) 3.92%  
Long-term debt $ 15,000 15,000
Series 2021B Senior Unsecured Notes    
Debt Instrument [Line Items]    
Rate (as a percent) 3.69%  
Long-term debt $ 100,000 100,000
Series 2022A Senior Unsecured Notes    
Debt Instrument [Line Items]    
Rate (as a percent) 3.77%  
Long-term debt $ 90,000 $ 90,000
v3.24.0.1
Short-Term and Long-Term Borrowings - Summary of Maturities of Long-term Debt (Details)
$ in Thousands
Dec. 31, 2023
USD ($)
Debt Disclosure [Abstract]  
2024 $ 0
2025 0
2026 80,000
2027 42,000
2028 $ 0
v3.24.0.1
Employee Postretirement Benefits - Narrative (Details)
$ in Thousands
 12 Months Ended
Dec. 31, 2023
USD ($)
year
Dec. 31, 2022
USD ($)
Dec. 31, 2021
USD ($)
Defined Benefit Plan Disclosure [Line Items]      
Payment for pension benefits $ 0 $ 20,000 $ 10,000
Defined contribution plan, cost $ 7,800 6,700 $ 6,500
Pension Benefits (Pension Plan)      
Defined Benefit Plan Disclosure [Line Items]      
Age for compensation | year 65    
Age below which compensation is reduced | year 62    
Vesting period 5 years    
Investment redemption, notice period 95 days    
Subscriptions, lock-up period 3 years    
Accumulated benefit obligation $ 288,800 $ 283,200  
Discount rate (as a percent) 5.57% 5.51%  
Decrease in benefit obligation for change in discount rate $ 2,200 $ 117,100  
Increase in benefit obligation for change in expected future compensation 7,900    
Increase from plan participant census data 3,100    
Actual returns 34,200    
Expected returns 25,900    
Obligation impact $ 8,300    
Other Postretirement Benefits Plan      
Defined Benefit Plan Disclosure [Line Items]      
Health insurance benefits, requisite age 55 years    
Health insurance benefits, requisite service period 10 years    
Reduction from plan amendment $ 20,100    
Reduction attributable to increase in discount rate to measurement plan liability $ 2,600    
Discount rate during time of amendment (as a percent) 6.06%    
Discount rate (as a percent) 5.53% 5.52%  
Savings attributable to the plan change $ 17,500    
Expected remaining service period (in years) 4 years 9 months 18 days    
Decrease in benefit obligation for change in discount rate $ 1,300 $ 17,900  
Increase in benefit obligation for change in expected healthcare cost trends 1,100    
Executive Survivor and Supplemental Retirement Plan      
Defined Benefit Plan Disclosure [Line Items]      
Accumulated benefit obligation $ 35,800 $ 35,600  
Discount rate (as a percent) 5.53% 5.51%  
Decrease in benefit obligation for change in discount rate $ 100 $ 10,200  
v3.24.0.1
Employee Postretirement Benefits - Summary of Asset Allocation Ranges By Asset Class and PBO Funded Status (Details) - Pension Benefits (Pension Plan)
Dec. 31, 2023
Dec. 31, 2022
Defined Benefit Plan Disclosure [Line Items]    
Actual Allocation 100.00% 100.00%
Return Enhancement    
Defined Benefit Plan Disclosure [Line Items]    
Actual Allocation 48.00% 48.00%
Return Enhancement | 35 - 60% | Minimum    
Defined Benefit Plan Disclosure [Line Items]    
Permitted Range 35.00%  
Return Enhancement | 35 - 60% | Maximum    
Defined Benefit Plan Disclosure [Line Items]    
Permitted Range 60.00%  
Risk Management    
Defined Benefit Plan Disclosure [Line Items]    
Actual Allocation 51.00% 51.00%
Risk Management | 40 - 80% | Minimum    
Defined Benefit Plan Disclosure [Line Items]    
Permitted Range 40.00%  
Risk Management | 40 - 80% | Maximum    
Defined Benefit Plan Disclosure [Line Items]    
Permitted Range 80.00%  
Alternatives    
Defined Benefit Plan Disclosure [Line Items]    
Actual Allocation 1.00% 1.00%
Alternatives | 0 - 20% | Minimum    
Defined Benefit Plan Disclosure [Line Items]    
Permitted Range 0.00%  
Alternatives | 0 - 20% | Maximum    
Defined Benefit Plan Disclosure [Line Items]    
Permitted Range 20.00%  
v3.24.0.1
Employee Postretirement Benefits - Summary of Allocation of Plan Assets (Details) - USD ($)
$ in Thousands
Dec. 31, 2023
Dec. 31, 2022
Defined Benefit Plan Disclosure [Line Items]    
Plan Assets $ 330,479 $ 313,797
Level 1    
Defined Benefit Plan Disclosure [Line Items]    
Plan Assets 328,961 310,094
Level 2    
Defined Benefit Plan Disclosure [Line Items]    
Plan Assets 0 0
Level 3    
Defined Benefit Plan Disclosure [Line Items]    
Plan Assets 0 0
NAV    
Defined Benefit Plan Disclosure [Line Items]    
Plan Assets 1,518 3,703
Equity Funds    
Defined Benefit Plan Disclosure [Line Items]    
Plan Assets 127,159 124,327
Equity Funds | Level 1    
Defined Benefit Plan Disclosure [Line Items]    
Plan Assets 127,159 124,327
Equity Funds | Level 2    
Defined Benefit Plan Disclosure [Line Items]    
Plan Assets 0 0
Equity Funds | Level 3    
Defined Benefit Plan Disclosure [Line Items]    
Plan Assets 0 0
Equity Funds | NAV    
Defined Benefit Plan Disclosure [Line Items]    
Plan Assets 0 0
Fixed Income Funds    
Defined Benefit Plan Disclosure [Line Items]    
Plan Assets 167,604 156,424
Fixed Income Funds | Level 1    
Defined Benefit Plan Disclosure [Line Items]    
Plan Assets 167,604 156,424
Fixed Income Funds | Level 2    
Defined Benefit Plan Disclosure [Line Items]    
Plan Assets 0 0
Fixed Income Funds | Level 3    
Defined Benefit Plan Disclosure [Line Items]    
Plan Assets 0 0
Fixed Income Funds | NAV    
Defined Benefit Plan Disclosure [Line Items]    
Plan Assets 0 0
Hybrid Funds    
Defined Benefit Plan Disclosure [Line Items]    
Plan Assets 10,980 9,756
Hybrid Funds | Level 1    
Defined Benefit Plan Disclosure [Line Items]    
Plan Assets 10,980 9,756
Hybrid Funds | Level 2    
Defined Benefit Plan Disclosure [Line Items]    
Plan Assets 0 0
Hybrid Funds | Level 3    
Defined Benefit Plan Disclosure [Line Items]    
Plan Assets 0 0
Hybrid Funds | NAV    
Defined Benefit Plan Disclosure [Line Items]    
Plan Assets 0 0
U.S. Treasury Securities    
Defined Benefit Plan Disclosure [Line Items]    
Plan Assets 23,218 19,587
U.S. Treasury Securities | Level 1    
Defined Benefit Plan Disclosure [Line Items]    
Plan Assets 23,218 19,587
U.S. Treasury Securities | Level 2    
Defined Benefit Plan Disclosure [Line Items]    
Plan Assets 0 0
U.S. Treasury Securities | Level 3    
Defined Benefit Plan Disclosure [Line Items]    
Plan Assets 0 0
U.S. Treasury Securities | NAV    
Defined Benefit Plan Disclosure [Line Items]    
Plan Assets 0 0
SEI Energy Debt Collective Fund    
Defined Benefit Plan Disclosure [Line Items]    
Plan Assets 1,518 3,703
SEI Energy Debt Collective Fund | Level 1    
Defined Benefit Plan Disclosure [Line Items]    
Plan Assets 0 0
SEI Energy Debt Collective Fund | Level 2    
Defined Benefit Plan Disclosure [Line Items]    
Plan Assets 0 0
SEI Energy Debt Collective Fund | Level 3    
Defined Benefit Plan Disclosure [Line Items]    
Plan Assets 0 0
SEI Energy Debt Collective Fund | NAV    
Defined Benefit Plan Disclosure [Line Items]    
Plan Assets $ 1,518 $ 3,703
v3.24.0.1
Employee Postretirement Benefits - Summary of Changes in Fair Value of Plan Assets and Plan's Benefit Obligations (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Change in Fair Value of Plan Assets:      
Fair Value of Plan Assets, beginning balance $ 313,797    
Fair Value of Plan Assets, ending balance 330,479 $ 313,797  
Pension Benefits (Pension Plan)      
Change in Fair Value of Plan Assets:      
Fair Value of Plan Assets, beginning balance 313,797 387,212  
Actual Return on Plan Assets 34,196 (76,485)  
Company Contributions 0 20,000  
Benefit Payments (17,514) (16,930)  
Participant Premium Payments 0 0  
Fair Value of Plan Assets, ending balance 330,479 313,797 $ 387,212
Change in Benefit Obligation:      
Projected Benefit Obligation, beginning balance 308,055 416,697  
Service Cost 3,698 6,576 7,462
Interest Cost 16,436 12,344 11,660
Benefit Payments (17,514) (16,930)  
Participant Premium Payments 0 0  
Plan Amendments 0 0  
Actuarial (Gain) Loss 8,126 (110,632)  
Projected Benefit Obligation, ending balance 318,801 308,055 416,697
Funded Status 11,678 5,742  
Amounts Recognized in Consolidated Balance Sheets at December 31:      
Noncurrent Assets 11,678 5,742  
Current Liabilities 0 0  
Noncurrent Liabilities and Deferred Credits 0 0  
Net Asset (Liability) 11,678 5,742  
Pension Benefits (ESSRP)      
Change in Fair Value of Plan Assets:      
Fair Value of Plan Assets, beginning balance 0 0  
Actual Return on Plan Assets 0 0  
Company Contributions 2,197 2,205  
Benefit Payments (2,197) (2,205)  
Participant Premium Payments 0 0  
Fair Value of Plan Assets, ending balance 0 0 0
Change in Benefit Obligation:      
Projected Benefit Obligation, beginning balance 35,624 46,840  
Service Cost 72 195 187
Interest Cost 1,889 1,341 1,228
Benefit Payments (2,197) (2,205)  
Participant Premium Payments 0 0  
Plan Amendments 0 0  
Actuarial (Gain) Loss 392 (10,547)  
Projected Benefit Obligation, ending balance 35,780 35,624 46,840
Funded Status (35,780) (35,624)  
Amounts Recognized in Consolidated Balance Sheets at December 31:      
Noncurrent Assets 0 0  
Current Liabilities (2,679) (2,414)  
Noncurrent Liabilities and Deferred Credits (33,101) (33,210)  
Net Asset (Liability) (35,780) (35,624)  
Postretirement Benefits      
Change in Fair Value of Plan Assets:      
Fair Value of Plan Assets, beginning balance 0 0  
Actual Return on Plan Assets 0 0  
Company Contributions 3,167 2,294  
Benefit Payments (8,900) (8,173)  
Participant Premium Payments 5,733 5,879  
Fair Value of Plan Assets, ending balance 0 0 0
Change in Benefit Obligation:      
Projected Benefit Obligation, beginning balance 49,947 69,311  
Service Cost 565 1,338 1,722
Interest Cost 2,416 2,041 1,891
Benefit Payments (8,900) (8,172)  
Participant Premium Payments 5,733 5,879  
Plan Amendments (17,493) 0  
Actuarial (Gain) Loss (2,123) (20,450)  
Projected Benefit Obligation, ending balance 30,145 49,947 $ 69,311
Funded Status (30,145) (49,947)  
Amounts Recognized in Consolidated Balance Sheets at December 31:      
Noncurrent Assets 0 0  
Current Liabilities (2,469) (2,970)  
Noncurrent Liabilities and Deferred Credits (27,676) (46,977)  
Net Asset (Liability) $ (30,145) $ (49,947)  
v3.24.0.1
Employee Postretirement Benefits - Summary of Assumptions Used to Determine Benefit Obligations (Details)
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Participants Age 40 to 49, Non-Union    
Defined Benefit Plan Disclosure [Line Items]    
Long-Term Rate of Compensation Increase 3.50%  
Participants Age 50 and Older, Non-Union    
Defined Benefit Plan Disclosure [Line Items]    
Long-Term Rate of Compensation Increase 3.00%  
Pension Benefits (Pension Plan)    
Defined Benefit Plan Disclosure [Line Items]    
Discount Rate 5.57% 5.51%
Pension Benefits (Pension Plan) | Participants to Age 39    
Defined Benefit Plan Disclosure [Line Items]    
Long-Term Rate of Compensation Increase 4.50% 4.50%
Pension Benefits (Pension Plan) | Participants Ages 40 to 49    
Defined Benefit Plan Disclosure [Line Items]    
Long-Term Rate of Compensation Increase 4.50% 3.50%
Pension Benefits (Pension Plan) | Participants Age 50 and Older    
Defined Benefit Plan Disclosure [Line Items]    
Long-Term Rate of Compensation Increase 3.75% 2.75%
Pension Benefits (ESSRP)    
Defined Benefit Plan Disclosure [Line Items]    
Discount Rate 5.53% 5.51%
Long-Term Rate of Compensation Increase 3.00% 3.00%
Postretirement Benefits    
Defined Benefit Plan Disclosure [Line Items]    
Discount Rate 5.53% 5.52%
Healthcare Cost Immediate Trend Rate 6.97% 7.50%
Healthcare Cost Ultimate Trend Rate 4.00% 4.00%
Year the Rate Reaches the Ultimate Trend Rate 2048 2048
v3.24.0.1
Employee Postretirement Benefits - Summary of Components of Net Periodic Benefit Cost (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Defined Benefit Plan Disclosure [Line Items]      
Net Periodic Benefit Cost $ (7,487) $ 5,913 $ 11,366
Pension Benefits (Pension Plan)      
Defined Benefit Plan Disclosure [Line Items]      
Service Cost 3,698 6,576 7,462
Interest Cost 16,436 12,344 11,660
Expected Return on Assets (25,914) (23,684) (22,359)
Amortization of Prior Service Cost 0 0 0
Amortization of Net Actuarial Loss 0 7,865 10,914
Net Periodic Benefit Cost (5,780) 3,101 7,677
Pension Benefits (ESSRP)      
Defined Benefit Plan Disclosure [Line Items]      
Service Cost 72 195 187
Interest Cost 1,889 1,341 1,228
Expected Return on Assets 0 0 0
Amortization of Prior Service Cost 0 0 0
Amortization of Net Actuarial Loss 0 567 620
Net Periodic Benefit Cost 1,961 2,103 2,035
Postretirement Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Service Cost 565 1,338 1,722
Interest Cost 2,416 2,041 1,891
Expected Return on Assets 0 0 0
Amortization of Prior Service Cost (6,649) (5,733) (5,733)
Amortization of Net Actuarial Loss 0 3,063 3,774
Net Periodic Benefit Cost $ (3,668) $ 709 $ 1,654
v3.24.0.1
Employee Postretirement Benefits - Summary of Composition of Periodic Benefit Cost (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Retirement Benefits [Abstract]      
Net Periodic Benefit Cost $ (7,487) $ 5,913 $ 11,366
Net Amount Amortized Due to the Effect of Regulation 1,225 1,121 21
Net Periodic Benefit Cost Recognized $ (6,262) $ 7,034 $ 11,387
v3.24.0.1
Employee Postretirement Benefits - Summary of Weighted-Average Assumptions Used to Determine Net Periodic Benefit Cost (Details)
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Pension Benefits (Pension Plan)      
Defined Benefit Plan Disclosure [Line Items]      
Discount Rate 5.51% 3.03% 2.78%
Long-Term Rate of Return on Plan Assets 7.00% 6.30% 6.51%
Pension Benefits (Pension Plan) | Participants to Age 39      
Defined Benefit Plan Disclosure [Line Items]      
Long-Term Rate of Compensation Increase 4.50% 4.50% 4.50%
Pension Benefits (Pension Plan) | Participants Ages 40 to 49      
Defined Benefit Plan Disclosure [Line Items]      
Long-Term Rate of Compensation Increase 3.50% 3.50% 3.50%
Pension Benefits (Pension Plan) | Participants Age 50 and Older      
Defined Benefit Plan Disclosure [Line Items]      
Long-Term Rate of Compensation Increase 2.75% 2.75% 2.75%
Pension Benefits (ESSRP)      
Defined Benefit Plan Disclosure [Line Items]      
Discount Rate 5.51% 2.93% 2.61%
Long-Term Rate of Compensation Increase 3.00% 3.00% 3.00%
Postretirement Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Discount Rate 5.52% 3.01% 2.75%
v3.24.0.1
Employee Postretirement Benefits - Summary of Amounts Recognized in Consolidated Balance Sheets (Details) - USD ($)
$ in Thousands
Dec. 31, 2023
Dec. 31, 2022
Pension Benefits (Pension Plan)    
Regulatory Assets (Liabilities):    
Unrecognized Prior Service Cost $ 0 $ 0
Unrecognized Actuarial Loss 85,227 85,367
Net Regulatory Assets (Liabilities) 85,227 85,367
Accumulated Other Comprehensive Income (Loss):    
Unrecognized Prior Service Cost 0 0
Unrecognized Actuarial Gain (Loss) 1,994 1,978
Total Accumulated Other Comprehensive Income (Loss) 1,994 1,978
Pension Benefits (ESSRP)    
Regulatory Assets (Liabilities):    
Unrecognized Prior Service Cost 0 0
Unrecognized Actuarial Loss 1,061 979
Net Regulatory Assets (Liabilities) 1,061 979
Accumulated Other Comprehensive Income (Loss):    
Unrecognized Prior Service Cost 0 0
Unrecognized Actuarial Gain (Loss) (1,403) (1,093)
Total Accumulated Other Comprehensive Income (Loss) (1,403) (1,093)
Postretirement Benefits    
Regulatory Assets (Liabilities):    
Unrecognized Prior Service Cost (18,845) (8,400)
Unrecognized Actuarial Loss 1,759 3,993
Net Regulatory Assets (Liabilities) (17,086) (4,407)
Accumulated Other Comprehensive Income (Loss):    
Unrecognized Prior Service Cost 498 99
Unrecognized Actuarial Gain (Loss) 707 818
Total Accumulated Other Comprehensive Income (Loss) $ 1,205 $ 917
v3.24.0.1
Employee Postretirement Benefits - Summary of Benefit Payments, Which Reflect Expected Future Service, As Appropriate, Expected to Be Paid Out From Plan Assets (Details)
$ in Thousands
Dec. 31, 2023
USD ($)
Defined Benefit Plan Disclosure [Line Items]  
2024 $ 24,067
2025 24,468
2026 25,195
2027 25,859
2028 26,296
2029-2033 136,773
Pension Benefits (Pension Plan)  
Defined Benefit Plan Disclosure [Line Items]  
2024 18,851
2025 19,274
2026 19,828
2027 20,318
2028 20,882
2029-2033 110,291
Pension Benefits (ESSRP)  
Defined Benefit Plan Disclosure [Line Items]  
2024 2,747
2025 2,697
2026 2,823
2027 2,994
2028 2,938
2029-2033 14,437
Postretirement Benefits  
Defined Benefit Plan Disclosure [Line Items]  
2024 2,469
2025 2,497
2026 2,544
2027 2,547
2028 2,476
2029-2033 $ 12,045
v3.24.0.1
Asset Retirement Obligations - Narrative (Details) - USD ($)
Dec. 31, 2023
Dec. 31, 2022
Asset Retirement Obligation Disclosure [Abstract]    
Asset retirement obligation, legally restricted assets, fair value $ 0  
Asset retirement obligation, current 100,000 $ 2,700,000
Asset retirement obligations, noncurrent $ 36,400,000 $ 22,500,000
v3.24.0.1
Asset Retirement Obligations - Summary of Change in Asset Retirement Obligation (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]    
Beginning Balance $ 25,182 $ 24,191
New Obligations Recognized 4,506 0
Adjustments Due to Revisions in Cash Flow Estimates 8,394 0
Accrued Accretion 1,191 991
Settlements (2,796) 0
Ending Balance $ 36,477 $ 25,182
v3.24.0.1
Income Taxes - Summary of Income Tax Expense (Benefit) (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Current      
Federal Income Taxes $ 41,253 $ 31,949 $ 6,806
State Income Taxes 15,126 9,568 939
Deferred      
Federal Income Taxes 9,832 22,480 18,180
State Income Taxes 3,676 9,943 10,716
Tax Credits      
North Dakota Wind Tax Credit Amortization, Net of Federal Tax (586) (586) (586)
Investment Tax Credit Amortization (3) (3) (3)
Income Tax Expense (Benefit) $ 69,298 $ 73,351 $ 36,052
v3.24.0.1
Income Taxes - Summary of Effective Income Tax Rate (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Income Tax Disclosure [Abstract]      
Income Taxes at Federal Statutory Rate $ 76,332 $ 75,082 $ 44,692
Increases (Decreases) in Tax from:      
State Taxes on Income, Net of Federal Tax 14,429 15,049 9,962
Production Tax Credits (PTCs) (17,394) (14,985) (12,503)
Amortization of Excess Deferred Income Taxes (2,205) (1,625) (4,262)
North Dakota Wind Tax Credit Amortization, Net of Federal Tax (586) (586) (586)
Other, Net (1,278) 416 (1,251)
Income Tax Expense (Benefit) $ 69,298 $ 73,351 $ 36,052
Increases (Decreases) in Tax from:      
Income Taxes at Federal Statutory Rate 21.00% 21.00% 21.00%
State Taxes on Income, Net of Federal Tax 4.00% 4.20% 4.70%
Production Tax Credits (PTCs) (4.80%) (4.20%) (5.90%)
Amortization of Excess Deferred Income Taxes (0.60%) (0.50%) (2.00%)
North Dakota Wind Tax Credit Amortization, Net of Federal Tax (0.20%) (0.20%) (0.30%)
Other, Net (0.30%) 0.20% (0.60%)
Income Taxes at Effective Tax Rate 19.10% 20.50% 16.90%
v3.24.0.1
Income Taxes - Summary of Deferred Tax Assets and Liabilities (Details) - USD ($)
$ in Thousands
Dec. 31, 2023
Dec. 31, 2022
Deferred Tax Assets    
Employee Benefits $ 39,959 $ 39,216
Regulatory Liabilities 56,479 57,353
Tax Credit Carryforwards 21,836 20,209
Cost of Removal 32,993 37,360
Asset Retirement Obligations 9,494 6,557
Net Operating Loss Carryforward 2,336 1,853
Other 11,310 5,550
Total Deferred Tax Assets 174,407 168,098
Deferred Tax Liabilities    
Differences Related to Property (347,885) (334,201)
Retirement Benefits Regulatory Asset (22,458) (22,789)
Pension Expense (24,875) (24,269)
Other (16,462) (8,141)
Total Deferred Tax Liabilities (411,680) (389,400)
Deferred Income Taxes $ (237,273) $ (221,302)
v3.24.0.1
Income Taxes - Summary of Expiration of Tax Net Operating Losses and Tax Credits Available (Details) - State and Local Jurisdiction
$ in Thousands
Dec. 31, 2023
USD ($)
Operating Loss Carryforwards [Line Items]  
Operating loss carryforwards $ 2,336
Tax credit carryforward, amount 21,836
2024-2029  
Operating Loss Carryforwards [Line Items]  
Operating loss carryforwards 211
Tax credit carryforward, amount 0
2030-2037  
Operating Loss Carryforwards [Line Items]  
Operating loss carryforwards 2,125
Tax credit carryforward, amount 0
2038-2043  
Operating Loss Carryforwards [Line Items]  
Operating loss carryforwards 0
Tax credit carryforward, amount $ 21,836
v3.24.0.1
Income Taxes - Summary of Unrecognized Tax Benefit Activity (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]      
Balance on January 1 $ 923 $ 827 $ 771
Increases for tax positions taken during a prior period 596 44 11
Increases for tax positions taken during the current period 163 260 189
Decreases due to settlements with taxing authorities 0 0 0
Decreases as a result of a lapse of applicable statutes of limitations (193) (208) (144)
Balance on December 31 $ 1,489 $ 923 $ 827
v3.24.0.1
Income Taxes - Narrative (Details)
 12 Months Ended
Dec. 31, 2023
Income Tax Disclosure [Abstract]  
Period for unrecognized tax benefits not expected change 12 months
v3.24.0.1
Commitments and Contingencies - Narrative (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Other Commitments [Line Items]      
Capacity and energy requirement costs $ 5.6 $ 13.1 $ 11.5
Coal purchase commitment costs 43.7 45.1 40.4
Land easement non-lease payments expense 1.8 $ 1.4 $ 1.3
OTP | Federal Energy Regulatory Commission      
Other Commitments [Line Items]      
Estimated liability of refund obligation 2.8    
OTP | Construction Programs      
Other Commitments [Line Items]      
Long-term purchase commitment, amount 17.1    
OTP | OTP Land Easements      
Other Commitments [Line Items]      
Long-term purchase commitment, amount $ 62.4    
Long-term purchase commitment, period 99 years    
v3.24.0.1
Commitments and Contingencies - Summary of Commitments Contractual Obligation Maturities (Details)
$ in Thousands
Dec. 31, 2023
USD ($)
OTP  
Land Easement Payments  
2024 $ 1,804
2025 1,840
2026 1,845
2027 1,882
2028 1,921
Beyond 2028 53,107
Land easement payments, total 62,399
Construction Program and Other Commitments | Subsidiaries  
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]  
2024 4,374
2025 4,051
2026 1,377
2027 594
2028 550
Beyond 2028 6,165
Commitments other than operating leases, total 17,111
Capacity and Energy Requirements | OTP  
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]  
2024 245
2025 217
2026 197
2027 197
2028 197
Beyond 2028 3,939
Commitments other than operating leases, total 4,992
Coal Purchase Commitments | OTP  
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]  
2024 24,691
2025 24,593
2026 25,374
2027 25,786
2028 25,344
Beyond 2028 359,610
Commitments other than operating leases, total $ 485,398
v3.24.0.1
Stockholders' Equity (Details) - USD ($)
$ in Thousands
 12 Months Ended
May 03, 2021
Dec. 31, 2023
Dec. 31, 2022
Class of Stock [Line Items]      
Total capitalization   $ 2,267,065 $ 2,041,138
OTP      
Class of Stock [Line Items]      
Equity to total capitalization ratio   54.20%  
Net assets restricted from distribution   $ 771,300  
Minimum | Minnesota Public Utilities Commission | OTP      
Class of Stock [Line Items]      
Public utilities, requested equity capital structure (as a percent)   48.30%  
Maximum | OTP      
Class of Stock [Line Items]      
Total capitalization   $ 2,000,000  
Maximum | Minnesota Public Utilities Commission | OTP      
Class of Stock [Line Items]      
Public utilities, requested equity capital structure (as a percent)   59.10%  
Second Shelf Registration      
Class of Stock [Line Items]      
Shelf registration (in shares) 1,500,000    
Number of shares issued (in shares)   105,663  
Number of shares available for grant (in shares)   1,145,330  
Cumulative Preferred Shares      
Class of Stock [Line Items]      
Preferred stock, shares authorized (in shares)   1,500,000  
Preferred stock, shares outstanding (in shares)   0 0
Cumulative Preference Shares      
Class of Stock [Line Items]      
Preferred stock, shares authorized (in shares)   1,000,000  
Preferred stock, shares outstanding (in shares)   0  
v3.24.0.1
Accumulated Other Comprehensive Income (Loss) (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
AOCI Attributable to Parent, Net of Tax [Roll Forward]      
Beginning balance $ 1,217,317 $ 990,777 $ 870,966
Other Comprehensive Income (Loss) Before Reclassifications, net of tax 239 6,898 1,506
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss) (6) 541 477
Total Other Comprehensive Income 233 7,439 1,983
Ending balance 1,443,006 1,217,317 990,777
Pension and Other Postretirement Benefits      
AOCI Attributable to Parent, Net of Tax [Roll Forward]      
Beginning balance 1,334 (6,537) (8,716)
Other Comprehensive Income (Loss) Before Reclassifications, net of tax 59 7,331 1,638
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss) (18) 540 541
Total Other Comprehensive Income 41 7,871 2,179
Ending balance 1,375 1,334 (6,537)
Net Unrealized Gain (Losses) on Available-for-Sale Securities      
AOCI Attributable to Parent, Net of Tax [Roll Forward]      
Beginning balance (419) 13 209
Other Comprehensive Income (Loss) Before Reclassifications, net of tax 180 (433) (132)
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss) 12 1 (64)
Total Other Comprehensive Income 192 (432) (196)
Ending balance (227) (419) 13
Accumulated Other Comprehensive Income (Loss)      
AOCI Attributable to Parent, Net of Tax [Roll Forward]      
Beginning balance 915 (6,524) (8,507)
Total Other Comprehensive Income 233 7,439 1,983
Ending balance $ 1,148 $ 915 $ (6,524)
v3.24.0.1
Share-Based Payments - Narrative (Details)
 1 Months Ended 12 Months Ended
Apr. 30, 2023
shares
Dec. 31, 2023
USD ($)
measure
$ / shares
shares
Dec. 31, 2022
USD ($)
$ / shares
shares
Dec. 31, 2021
USD ($)
$ / shares
shares
Restricted Stock Awards        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Award cliff vesting period   4 years    
Granted (in dollars per share) | $ / shares   $ 68.03 $ 59.95 $ 43.55
Fair value of awards vested   $ 3,100,000 $ 3,000,000 $ 2,100,000
Unrecognized compensation costs   $ 3,400,000    
Unrecognized compensation costs, period of recognition   1 year 8 months 12 days    
Restricted Stock Awards | Minimum        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Award vesting period   3 years    
Restricted Stock Awards | Maximum        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Award vesting period   4 years    
Stock Performance Awards        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Award vesting period   3 years    
Granted (in dollars per share) | $ / shares   $ 61.97 $ 54.91 $ 38.34
Fair value of awards vested   $ 5,300,000 $ 5,100,000 $ 2,500,000
Unrecognized compensation costs   $ 400,000    
Unrecognized compensation costs, period of recognition   8 months 1 day    
Number of performance measures | measure   2    
Expected volatility rate measurement period   5 years    
Stock Performance Awards | Minimum        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Percentage of target amount as actual payment (as a percent)   0.00%    
Stock Performance Awards | Maximum        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Percentage of target amount as actual payment (as a percent)   150.00%    
The 1999 Employee Stock Purchase Plan        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Share-based payment awards, number of shares authorized (in shares) | shares   1,400,000    
Discount from market price rate (as a percent)   15.00%    
Maximum number of shares available to be purchased per participant (in shares) | shares   2,000    
Purchase period   6 months    
Maximum employee subscription amount   $ 25,000    
Shares holding period   18 months    
Share-based payment arrangement, expense   $ 300,000 $ 300,000 $ 200,000
Shares issued under the plan (in shares) | shares   26,348 26,420 27,975
Number of shares available for grant (in shares) | shares   237,367    
The 1999 Employee Stock Purchase Plan | Minimum        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Employee monthly withholding amounts   $ 10    
The 1999 Employee Stock Purchase Plan | Maximum        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Employee monthly withholding amounts   2,000    
The 2023 Stock Incentive Plan        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Share-based payment awards, number of shares authorized (in shares) | shares 979,891      
Share-based payment arrangement, expense   $ 7,400,000 $ 6,600,000 $ 6,700,000
Number of additional shares authorized (in shares) | shares 500,000      
Number of shares available for grant (in shares) | shares   943,192,000    
Share-based payment arrangement, expense, tax benefit   $ 1,600,000 $ 1,700,000 $ 1,800,000
v3.24.0.1
Share-Based Payments - Summary of Restricted Stock Awards and Stock Performance Awards (Details) - $ / shares
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Restricted Stock Awards      
Shares      
Beginning of year (in shares) 141,551    
Granted (in shares) 55,205    
Vested (in shares) (45,493)    
Forfeited (in shares) (2,350)    
End of year (in shares) 148,913 141,551  
Weighted-Average Grant-Date Fair Value      
Beginning of year (in dollars per share) $ 49.83    
Granted (in dollars per share) 68.03 $ 59.95 $ 43.55
Vested (in dollars per share) 50.02    
Forfeited (in dollars per share) 52.02    
End of year (in dollars per share) $ 56.48 $ 49.83  
Stock Performance Awards      
Shares      
Beginning of year (in shares) 189,800    
Granted (in shares) 59,400    
Vested (in shares) (55,000)    
Forfeited (in shares) 0    
End of year (in shares) 194,200 189,800  
Weighted-Average Grant-Date Fair Value      
Beginning of year (in dollars per share) $ 45.95    
Granted (in dollars per share) 61.97 $ 54.91 $ 38.34
Vested (in dollars per share) 47.79    
Forfeited (in dollars per share) 0    
End of year (in dollars per share) $ 50.33 $ 45.95  
v3.24.0.1
Share-Based Payments - Summary of Weighted-Average Assumptions (Details) - Stock Performance Awards
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Risk-free interest rate 4.15% 1.52% 0.18%
Expected term (in years) 3 years 3 years 3 years
Expected volatility 34.00% 32.00% 32.00%
Dividend yield 2.50% 2.90% 3.60%
v3.24.0.1
Earnings Per Share (Details) - shares
shares in Thousands
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]      
Weighted Average Common Shares Outstanding - Basic (in shares) 41,668 41,586 41,491
Effect of Dilutive Securities:      
Total Dilutive Shares (in shares) 371 345 327
Weighted Average Common Shares Outstanding – Diluted (in shares) 42,039 41,931 41,818
Stock Performance Awards      
Effect of Dilutive Securities:      
Effect of Dilutive Securities (in shares) 269 248 226
Restricted Stock Awards      
Effect of Dilutive Securities:      
Effect of Dilutive Securities (in shares) 100 95 87
Employee Stock Purchase Plan Shares and Other      
Effect of Dilutive Securities:      
Effect of Dilutive Securities (in shares) 2 2 14
v3.24.0.1
Derivative Instruments (Details)
$ in Millions
 12 Months Ended
Dec. 31, 2023
USD ($)
MWh
Dec. 31, 2022
USD ($)
MWh
Derivative Instruments and Hedging Activities Disclosures [Line Items]    
Notional amount of outstanding swap agreements | MWh 187,400 295,000
Derivative liability $ 4.2 $ 7.1
Derivative Liability, Statement of Financial Position [Extensible Enumeration] Other Current Liabilities Other Current Liabilities
Swap    
Derivative Instruments and Hedging Activities Disclosures [Line Items]    
Gain (loss) on derivatives, net $ 16.5 $ 1.0
v3.24.0.1
Fair Value Measurements - Summary of Fair Value Measurements, Recurring and Nonrecurring (Details) - USD ($)
$ in Thousands
Dec. 31, 2023
Dec. 31, 2022
Assets:    
Debt securities $ 9,303 $ 8,761
Level 1 | Fair Value, Recurring    
Assets:    
Money Market Funds 3,125 1,560
Mutual Funds 7,771 5,503
Total Assets 10,896 7,063
Liabilities:    
Derivative Instruments 0 0
Total 0 0
Level 1 | Fair Value, Recurring | Corporate Debt Securities    
Assets:    
Debt securities 0 0
Level 1 | Fair Value, Recurring | Government Debt Securities    
Assets:    
Debt securities 0 0
Level 2 | Fair Value, Recurring    
Assets:    
Money Market Funds 0 0
Mutual Funds 0 0
Total Assets 9,303 8,761
Liabilities:    
Derivative Instruments 4,210 7,130
Total 4,210 7,130
Level 2 | Fair Value, Recurring | Corporate Debt Securities    
Assets:    
Debt securities 1,579 1,434
Level 2 | Fair Value, Recurring | Government Debt Securities    
Assets:    
Debt securities 7,724 7,327
Level 3 | Fair Value, Recurring    
Assets:    
Money Market Funds 0 0
Mutual Funds 0 0
Total Assets 0 0
Liabilities:    
Derivative Instruments 0 0
Total 0 0
Level 3 | Fair Value, Recurring | Corporate Debt Securities    
Assets:    
Debt securities 0 0
Level 3 | Fair Value, Recurring | Government Debt Securities    
Assets:    
Debt securities $ 0 $ 0
v3.24.0.1
Fair Value Measurements - Summary of Fair Value of Assets and Liabilities (Details) - USD ($)
$ in Thousands
Dec. 31, 2023
Dec. 31, 2022
Carrying Amount    
Assets:    
Cash and Cash Equivalents $ 230,373 $ 118,996
Total Assets 230,373 118,996
Liabilities:    
Short-Term Debt 81,422 8,204
Long-Term Debt 824,059 823,821
Total 905,481 832,025
Fair Value    
Assets:    
Cash and Cash Equivalents 230,373 118,996
Total Assets 230,373 118,996
Liabilities:    
Short-Term Debt 81,422 8,204
Long-Term Debt 710,839 681,615
Total $ 792,261 $ 689,819
v3.24.0.1
Schedule I - Condensed Financial Information of Registrant - CONDENSED BALANCE SHEETS, PARENT COMPANY (Details) - USD ($)
$ in Thousands
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Dec. 31, 2020
Current Assets        
Cash and Cash Equivalents $ 230,373 $ 118,996    
Accounts Receivable from Subsidiaries 157,143 144,393    
Other 16,826 18,412    
Total Current Assets 570,170 452,752    
Investments in Subsidiaries 62,516 54,845    
Other Noncurrent Assets 51,377 41,177    
Total Assets 3,242,568 2,901,661    
Current Liabilities        
Accounts Payable to Subsidiaries 94,428 104,400    
Other 43,775 56,065    
Total Current Liabilities 309,757 237,636    
Other Noncurrent Liabilities 75,977 60,985    
Commitments and Contingencies (Note 13)    
Capitalization        
Long-Term Debt 824,059 823,821    
Total Shareholders' Equity 1,443,006 1,217,317 $ 990,777 $ 870,966
Total Capitalization 2,267,065 2,041,138    
Total Liabilities and Shareholders' Equity 3,242,568 2,901,661    
OTC        
Current Assets        
Cash and Cash Equivalents 228,137 119,246    
Other 977 1,045    
Total Current Assets 231,786 123,686    
Deferred Income Taxes 65,244 64,802    
Other Noncurrent Assets 50,795 43,779    
Total Assets 2,152,309 1,775,165    
Current Liabilities        
Other 15,320 15,994    
Total Current Liabilities 583,999 436,364    
Other Noncurrent Liabilities 45,455 41,686    
Commitments and Contingencies (Note 13)    
Capitalization        
Long-Term Debt 79,849 79,798    
Total Shareholders' Equity 1,443,006 1,217,317    
Total Capitalization 1,522,855 1,297,115    
Total Liabilities and Shareholders' Equity 2,152,309 1,775,165    
OTC | Subsidiaries        
Current Assets        
Accounts Receivable from Subsidiaries 2,555 3,278    
Interest Receivable from Subsidiaries 117 117    
Investments in Subsidiaries 1,725,584 1,463,998    
Notes Receivable from Subsidiaries 78,900 78,900    
Current Liabilities        
Accounts Payable to Subsidiaries 7 7    
Notes Payable to Subsidiaries $ 568,672 $ 420,363    
v3.24.0.1
Schedule I - Condensed Financial Information of Registrant - CONDENSED STATEMENTS OF INCOME, PARENT COMPANY (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Income      
Other Income $ 12,650 $ 2,037 $ 2,900
Expense      
Nonelectric Selling, General, and Administrative Expenses 72,663 69,718 65,394
Interest Expense 37,677 36,016 37,771
Nonservice Cost Components of Postretirement Benefits (10,597) (1,075) 2,016
Income Before Income Taxes 363,489 357,535 212,821
Income Tax Benefit (69,298) (73,351) (36,052)
Net Income 294,191 284,184 176,769
OTC      
Income      
Other Income 10,496 466 1,290
Total Income 307,861 300,681 192,491
Expense      
Nonelectric Selling, General, and Administrative Expenses 12,816 17,269 14,825
Nonservice Cost Components of Postretirement Benefits 1,063 1,023 1,097
Total Expense 17,698 22,363 20,652
Income Before Income Taxes 290,163 278,318 171,839
Income Tax Benefit 4,028 5,866 4,930
Net Income 294,191 284,184 176,769
OTC | Subsidiaries      
Income      
Equity Income in Earnings of Subsidiaries 294,467 296,833 188,375
Interest Income from Subsidiaries 2,898 3,382 2,826
Expense      
Interest Expense 6 5 3
OTC | Nonrelated Party      
Expense      
Interest Expense $ 3,813 $ 4,066 $ 4,727
v3.24.0.1
Schedule I - Condensed Financial Information of Registrant - CONDENSED STATEMENTS OF CASH FLOWS , PARENT COMPANY (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Cash Flows from Operating Activities      
Net Cash Provided by Operating Activities $ 404,499 $ 389,309 $ 231,243
Cash Flows from Investing Activities      
Investment in Subsidiaries (8,378) (8,283) (9,383)
Net Cash Used in Investing Activities (289,287) (175,071) (171,510)
Cash Flows from Financing Activities      
Net (Repayments) Borrowings on Short-Term Debt 73,218 (82,959) 10,166
Proceeds from Issuance of Common Stock 0 0 696
Payments for Shares Withheld for Employee Tax Obligations (3,088) (2,942) (1,507)
Payments for Retirement of Long-Term Debt 0 (30,000) (140,169)
Dividends Paid (73,061) (68,755) (64,864)
Other, net (904) (2,123) (3,681)
Net Cash Used in Financing Activities (3,835) (96,779) (59,359)
Net Change in Cash and Cash Equivalents 111,377 117,459 374
Cash and Cash Equivalents at Beginning of Period 118,996 1,537 1,163
Cash and Cash Equivalents at End of Period 230,373 118,996 1,537
OTC      
Cash Flows from Operating Activities      
Net Cash Provided by Operating Activities 77,139 28,807 60,695
Cash Flows from Investing Activities      
Other, net (68) (1,695) (884)
Net Cash Used in Investing Activities (40,068) (51,695) (715)
Cash Flows from Financing Activities      
Net (Repayments) Borrowings on Short-Term Debt 0 (22,637) (42,529)
Borrowings from Subsidiaries 148,308 236,926 49,085
Proceeds from Issuance of Common Stock 0 0 696
Payments for Shares Withheld for Employee Tax Obligations (3,088) (2,942) (1,507)
Payments for Retirement of Long-Term Debt 0 0 (169)
Dividends Paid (73,061) (68,755) (64,864)
Other, net (339) (461) (689)
Net Cash Used in Financing Activities 71,820 142,131 (59,977)
Net Change in Cash and Cash Equivalents 108,891 119,243 3
Cash and Cash Equivalents at Beginning of Period 119,246 3 0
Cash and Cash Equivalents at End of Period 228,137 119,246 3
OTC | Subsidiaries      
Cash Flows from Investing Activities      
Investment in Subsidiaries (40,000) (50,000) 0
Debt Repaid by Subsidiaries $ 0 $ 0 $ 169
v3.24.0.1
Schedule I - Condensed Financial Information of Registrant - Summary of Related Party Transactions (Details) - USD ($)
$ in Thousands
Dec. 31, 2023
Dec. 31, 2022
Related Party Transaction [Line Items]    
Accounts Receivable $ 157,143 $ 144,393
Accounts Payable 94,428 104,400
Otter Tail Corporation | Subsidiaries    
Related Party Transaction [Line Items]    
Accounts Receivable 2,555 3,278
Interest Receivable 117 117
Long-Term Notes Receivable 78,900 78,900
Accounts Payable 7 7
Current Notes Payable 568,672 420,363
Otter Tail Corporation | Subsidiaries | Otter Tail Power Company    
Related Party Transaction [Line Items]    
Accounts Receivable 2,415 3,016
Interest Receivable 0 0
Long-Term Notes Receivable 0 0
Accounts Payable 7 7
Current Notes Payable 0 0
Otter Tail Corporation | Subsidiaries | Northern Pipe Products, Inc.    
Related Party Transaction [Line Items]    
Accounts Receivable 0 0
Interest Receivable 7 7
Long-Term Notes Receivable 5,000 5,000
Accounts Payable 0 0
Current Notes Payable 56,917 77,182
Otter Tail Corporation | Subsidiaries | Vinyltech Corporation    
Related Party Transaction [Line Items]    
Accounts Receivable 14 0
Interest Receivable 17 18
Long-Term Notes Receivable 11,500 11,500
Accounts Payable 0 0
Current Notes Payable 98,016 90,425
Otter Tail Corporation | Subsidiaries | BTD Manufacturing, Inc.    
Related Party Transaction [Line Items]    
Accounts Receivable 0 0
Interest Receivable 78 77
Long-Term Notes Receivable 52,000 52,000
Accounts Payable 0 0
Current Notes Payable 6,291 693
Otter Tail Corporation | Subsidiaries | T.O. Plastics, Inc.    
Related Party Transaction [Line Items]    
Accounts Receivable 36 20
Interest Receivable 15 15
Long-Term Notes Receivable 10,400 10,400
Accounts Payable 0 0
Current Notes Payable 980 5,855
Otter Tail Corporation | Subsidiaries | Varistar Corporation    
Related Party Transaction [Line Items]    
Accounts Receivable 0 0
Interest Receivable 0 0
Long-Term Notes Receivable 0 0
Accounts Payable 0 0
Current Notes Payable 406,468 246,208
Otter Tail Corporation | Subsidiaries | Otter Tail Assurance Limited    
Related Party Transaction [Line Items]    
Accounts Receivable 90 242
Interest Receivable 0 0
Long-Term Notes Receivable 0 0
Accounts Payable 0 0
Current Notes Payable $ 0 $ 0
v3.24.0.1
Schedule I - Condensed Financial Information of Registrant - Summary of Dividends (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Condensed Financial Information Disclosure [Abstract]      
Cash Dividends Paid to Parent by Subsidiaries $ 72,982 $ 68,680 $ 64,790
v3.24.0.1
Schedule II - Valuation and Qualifying Accounts and Reserves (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Allowance for Credit Losses      
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]      
Balance, January 1 $ 1,648 $ 1,836 $ 3,215
Charged to Cost and Expenses 2,014 909 93
Deductions (1,140) (1,097) (1,472)
Balance, December 31 2,522 1,648 1,836
Deferred Tax Asset Valuation Allowance      
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]      
Balance, January 1 0 0 800
Charged to Cost and Expenses 0 0 0
Deductions 0 0 (800)
Balance, December 31 $ 0 $ 0 $ 0