MDU Resources (MDU) 10-K 20 Feb 25 2024 FY Annual report Financial data

Cover Page

Cover Page - USD ($)	12 Months Ended
	Dec. 31, 2024	Feb. 13, 2025	Jun. 28, 2024
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2024
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	1-03480
Entity Registrant Name	MDU RESOURCES GROUP, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	30-1133956
Entity Address, Address Line One	1200 West Century Avenue
Entity Address, Address Line Two	P.O. Box 5650
Entity Address, City or Town	Bismarck
Entity Address, State or Province	ND
Entity Address, Postal Zip Code	58506-5650
City Area Code	701
Local Phone Number	530-1000
Title of 12(b) Security	Common Stock, par value $1.00 per share
Trading Symbol	MDU
Security Exchange Name	NYSE
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Document Financial Statement Error Correction	false
Entity Shell Company	false
Entity Public Float			$ 5,095,923,531
Entity Common Stock, Shares Outstanding		204,331,170
Documents Incorporated by Reference	Relevant portions of the registrant's 2025 Proxy Statement, to be filed no later than 120 days from December 31, 2024, are incorporated by reference in Part III, Items 10, 11, 12, 13 and 14 of this Report.
Entity Central Index Key	0000067716
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	FY
Amendment Flag	false

Audit Information

Audit Information	12 Months Ended
	Dec. 31, 2024
Audit Information [Abstract]
Auditor Location	Minneapolis, Minnesota
Auditor Name	Deloitte & Touche LLP
Auditor Firm ID	34

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Income Statement [Abstract]
External operating revenues	$ 1,757,978	$ 1,803,352	$ 1,747,298
Operating expenses:
Purchased natural gas sold	630,403	742,965	757,883
Electric fuel and purchased power	141,148	134,779	119,405
Operation and maintenance	414,491	407,081	379,951
Depreciation and amortization	200,078	190,450	188,560
Taxes, other than income	106,216	103,133	100,629
Total operating expenses	1,492,336	1,578,408	1,546,428
Operating income	265,642	224,944	200,870
Realized gain on tax-free exchange of the retained shares in Knife River	0	186,556	0
Other income	41,367	33,454	3,260
Interest expense	108,347	104,624	80,683
Income before income taxes	198,662	340,330	123,447
Income taxes	17,589	10,213	6,195
Income from continuing operations	181,073	330,117	117,252
Discontinued operations, net of tax	100,035	84,590	250,237
Net income	$ 281,108	$ 414,707	$ 367,489
Earnings per share - basic:
Income from continuing operations (in usd per share)	$ 0.89	$ 1.62	$ 0.58
Discontinued operations, net of tax (in usd per share)	0.49	0.42	1.23
Earnings per share - basic (in usd per share)	1.38	2.04	1.81
Earnings per share - diluted:
Income from continuing operations (in usd per share)	0.88	1.62	0.58
Discontinued operations, net of tax (in usd per share)	0.49	0.41	1.23
Earnings per share - diluted (in usd per share)	$ 1.37	$ 2.03	$ 1.81
Weighted average common shares outstanding - basic (in shares)	203,867	203,640	203,358
Weighted average common shares outstanding - diluted (in shares)	204,653	203,938	203,462

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Statement of Comprehensive Income [Abstract]
Net income	$ 281,108	$ 414,707	$ 367,489
Other comprehensive income (loss):
Reclassification adjustment for loss on derivative instruments included in net income, net of tax of $0, $15 and $177 in 2024, 2023 and 2022, respectively	0	81	413
Postretirement liability adjustment:
Postretirement liability gains (losses) arising during the period, net of tax of $360, $(201) and $3,965 in 2024, 2023 and 2022, respectively	1,049	(646)	12,007
Amortization of postretirement liability losses included in net periodic benefit credit, net of tax of $145, $78 and $597 in 2024, 2023 and 2022, respectively	432	242	1,819
Reclassification of postretirement liability adjustment from regulatory asset, net of tax of $0, $0 and $(1,086) in 2024, 2023 and 2022, respectively	0	0	(3,265)
Postretirement liability adjustment	1,481	(404)	10,561
Net unrealized gain (loss) on available-for-sale investments:
Net unrealized gain (loss) on available-for-sale investments arising during the period, net of tax of $23, $46 and $(177) in 2024, 2023 and 2022, respectively	85	173	(667)
Reclassification adjustment for loss on available-for-sale investments included in net income, net of tax of $5, $11 and $31 in 2024, 2023 and 2022, respectively	20	43	114
Net unrealized gain (loss) on available-for-sale investments	105	216	(553)
Other comprehensive income (loss)	1,586	(107)	10,421
Comprehensive income attributable to common stockholders	$ 282,694	$ 414,600	$ 377,910

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Current assets:
Cash, cash equivalents and restricted cash	$ 66,904	$ 60,473
Receivables, net	274,303	250,153
Current regulatory assets	215,436	172,492
Inventories	44,940	44,684
Prepayments and other current assets	64,676	66,431
Current assets of discontinued operations	0	769,490
Total current assets	666,259	1,363,723
Noncurrent assets:
Property, plant and equipment	7,554,063	7,081,267
Less accumulated depreciation and amortization	2,209,771	2,076,375
Net property, plant and equipment	5,344,292	5,004,892
Goodwill	345,736	345,736
Regulatory assets	322,350	447,099
Investments	115,459	112,475
Other	244,722	211,369
Noncurrent assets of discontinued operations	0	347,865
Total noncurrent assets	6,372,559	6,469,436
Total assets	7,038,818	7,833,159
Current liabilities:
Short-term borrowings	0	95,000
Long-term debt due within one year	161,700	61,319
Accounts payable	150,070	159,975
Regulatory liabilities due within one year	137,167	70,761
Taxes payable	43,372	49,553
Dividends payable	26,511	25,461
Accrued compensation	35,264	40,792
Other accrued liabilities	124,514	129,592
Current liabilities of discontinued operations	0	443,280
Total current liabilities	678,598	1,075,733
Noncurrent liabilities:
Long-term debt	2,130,910	2,104,904
Deferred income taxes	441,320	452,336
Regulatory liabilities	459,170	521,050
Asset retirement obligations	406,351	384,371
Other	231,895	209,882
Noncurrent liabilities of discontinued operations	0	179,650
Total noncurrent liabilities	3,669,646	3,852,193
Commitments and contingencies
Stockholders' equity:
Common stock Authorized - 500,000,000 shares, $1.00 par value Shares issued - 203,934,578 at December 31, 2024 and 203,689,090 at December 31, 2023	203,935	203,689
Other paid-in capital	1,473,738	1,466,235
Retained earnings	1,029,699	1,253,693
Accumulated other comprehensive loss	(16,798)	(18,384)
Total stockholders' equity	2,690,574	2,905,233
Total liabilities and stockholders' equity	$ 7,038,818	$ 7,833,159

Consolidated Statements of Equi

Consolidated Statements of Equity - USD ($) $ in Thousands	Total	Common Stock	Other Paid-in Capital	Retained Earnings	Total Accumulated Other Comprehensive Loss	Treasury Stock
Common stock, beginning balance (in shares) at Dec. 31, 2021		203,889,661
Beginning balance at Dec. 31, 2021	$ 3,382,874	$ 203,889	$ 1,461,205	$ 1,762,410	$ (41,004)	$ (3,626)
Treasury stock, common, beginning balance (in shares) at Dec. 31, 2021						(538,921)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	367,489			367,489
Other comprehensive income (loss)	10,421				10,421
Dividends declared on common stock	(178,761)			(178,761)
Employee stock-based compensation	10,254		10,254
Repurchase of common stock (in shares)						(266,821)
Repurchase of common stock	(7,399)					$ (7,399)
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings (in shares)						266,821
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings	(4,904)		(12,303)			$ 7,399
Issuance of common stock (in shares)		273,153
Issuance of common stock	7,155	$ 274	6,881
Common stock, ending balance (in shares) at Dec. 31, 2022		204,162,814
Ending balance at Dec. 31, 2022	3,587,129	$ 204,163	1,466,037	1,951,138	(30,583)	$ (3,626)
Treasury stock, common, ending balance (in shares) at Dec. 31, 2022						(538,921)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	414,707			414,707
Other comprehensive income (loss)	(107)				(107)
Dividends declared on common stock	(142,033)			(142,033)
Employee stock-based compensation	6,781		6,781
Repurchase of common stock (in shares)						(153,622)
Repurchase of common stock	(4,811)					$ (4,811)
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings (in shares)						153,622
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings	(3,040)		(7,851)			$ 4,811
Separation of Knife River and Everus (in shares)		(538,921)				(538,921)
Separation of Knife River and Everus	(954,726)	$ (539)		(970,119)	12,306	$ 3,626
Issuance of common stock (in shares)		65,197
Issuance of common stock	$ 1,333	$ 65	1,268
Common stock, ending balance (in shares) at Dec. 31, 2023	203,689,090	203,689,090
Ending balance at Dec. 31, 2023	$ 2,905,233	$ 203,689	1,466,235	1,253,693	(18,384)	$ 0
Treasury stock, common, ending balance (in shares) at Dec. 31, 2023						0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	281,108			281,108
Other comprehensive income (loss)	1,586				1,586
Dividends declared on common stock	(104,786)			(104,786)
Employee stock-based compensation	9,572		9,572
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings (in shares)		199,147
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings	(2,623)	$ 199	(2,822)
Separation of Knife River and Everus	(400,316)			(400,316)
Issuance of common stock (in shares)		46,341
Issuance of common stock	$ 800	$ 47	753
Common stock, ending balance (in shares) at Dec. 31, 2024	203,934,578	203,934,578
Ending balance at Dec. 31, 2024	$ 2,690,574	$ 203,935	$ 1,473,738	$ 1,029,699	$ (16,798)	$ 0
Treasury stock, common, ending balance (in shares) at Dec. 31, 2024						0

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2024		Dec. 31, 2023		Dec. 31, 2022
Operating activities:
Net income		$ 281,108		$ 414,707		$ 367,489
Income from discontinued operations, net of tax		100,035		84,590		250,237
Income from continuing operations		181,073		330,117		117,252
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization		200,078		190,450		188,560
Deferred income taxes		(16,078)		(1,309)		20,187
Provision for credit losses		6,558		7,422		5,409
Amortization of debt issuance costs		1,828		1,013		885
Employee stock-based compensation costs		8,423		5,505		7,913
Pension and postretirement benefit plan net periodic benefit credit		(3,837)		(5,380)		(7,323)
Unrealized (gains) losses on investments		(5,942)		(7,431)		10,119
(Gains) losses on sales of assets		(857)		(347)		15
Gain on tax-free exchange of the retained shares in Knife River		0		(186,556)		0
Changes in current assets and liabilities, net of acquisitions:
Receivables		(30,310)		79,111		(91,193)
Inventories		246		(21,729)		243
Other current assets		80,977		(48,492)		14,522
Accounts payable		(443)		(87,209)		84,547
Other current liabilities		(5,252)		73,365		(26,873)
Pension and postretirement benefit plan contributions		(3,000)		(7,643)		(81)
Other noncurrent changes		(1,651)		(15,554)		(2,567)
Net cash provided by continuing operations		411,813		305,333		321,615
Net cash provided by discontinued operations		90,505		27,294		188,449
Net cash provided by operating activities		502,318		332,627		510,064
Investing activities:
Capital expenditures		(522,824)		(484,136)		(442,582)
Net proceeds from sale or disposition of property		691		260		3
Cost of removal, net of salvage value		(5,539)		1,170		(11,779)
Investments		(5,155)		(2,423)		(2,571)
Proceeds from investment cost basis withdrawal		9,000		20,000		0
Net cash used in continuing operations		(523,827)		(465,129)		(456,929)
Net cash used in discontinued operations		(28,858)		(75,662)		(181,952)
Net cash used in investing activities		(552,685)		(540,791)		(638,881)
Financing activities:
Issuance of short-term borrowings		0		810,000		11,500
Repayment of short-term borrowings		(95,000)		(433,901)		0
Issuance of long-term debt		308,600		594,700		214,969
Repayment of long-term debt		(182,135)		(568,883)		(38,764)
Debt issuance costs		(2,456)		(2,521)		(1,129)
Costs of issuance of common stock		(50)		0		(150)
Dividends paid		(102,939)		(161,316)		(176,915)
Repurchase of common stock		0		(4,811)		(7,399)
Tax withholding on stock-based compensation		(2,623)		(3,040)		(4,904)
Net cash (used in) provided by continuing operations		(76,603)		230,228		(2,792)
Net cash provided by (used in) discontinued operations		116,899		(25,606)		157,965
Net cash provided by financing activities		40,296		204,622		155,173
(Decrease) increase in cash, cash equivalents and restricted cash		(10,071)		(3,542)		26,356
Cash, cash equivalents and restricted cash - beginning of year		76,975	[1]	80,517	[1]	54,161
Cash, cash equivalents and restricted cash - end of year	[1]	$ 66,904		$ 76,975		$ 80,517
[1] *Includes cash of discontinued operations of $16.5 million and $9.7 million for the years ended December 31, 2023 and 2022, respectively.

Consolidated Statements of Co_2

Consolidated Statements of Comprehensive Income (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Statement of Comprehensive Income [Abstract]
Reclassification adjustment for loss on derivative instruments included in net income, tax	$ 0	$ 15	$ 177
Postretirement liability gains (losses) arising during the period, tax	360	(201)	3,965
Amortization of postretirement liability losses included in net periodic benefit credit, tax	145	78	597
Reclassification of postretirement liability adjustment from regulatory asset, tax	0	0	(1,086)
Net unrealized loss on available-for-sale investments arising during the period, tax	23	46	(177)
Reclassification adjustment for loss on available-for-sale investments included in net income, tax	$ 5	$ 11	$ 31

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2024	Dec. 31, 2023
Statement of Financial Position [Abstract]
Common stock, authorized (in shares)	500,000,000	500,000,000
Common stock, par value per share (in usd per share)	$ 1	$ 1
Common stock, issued (in shares)	203,934,578	203,689,090

Consolidated Statements of Ca_2

Consolidated Statements of Cash Flows (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Statement of Cash Flows [Abstract]
Disposal group, including discontinued operation, cash and cash equivalents	$ 16.5	$ 9.7

Basis of Presentation

Basis of Presentation	12 Months Ended
	Dec. 31, 2024
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The consolidated financial statements of the Company include the accounts of the following businesses: electric, natural gas distribution, pipeline and other. For further descriptions of the Company's businesses, see Note 17. On May 31, 2023, the Company completed the separation of Knife River, formerly the construction materials and contracting segment, resulting in Knife River becoming an independent, publicly-traded company. The Company's board of directors approved the distribution of approximately 90 percent of the issued and outstanding shares of Knife River to the Company's stockholders. Stockholders of the Company received one share of Knife River common stock for every four shares of the Company's common stock held on May 22, 2023, the record date for the distribution. The Company retained approximately 10 percent or 5.7 million shares of Knife River common stock immediately following the separation, which were disposed of in a tax-free exchange in November 2023. The separation of Knife River was a tax-free spinoff transaction to the Company's stockholders for U.S. federal income tax purposes, except for cash received in lieu of fractional shares. On October 31, 2024, the Company completed the separation of Everus, its construction services business, resulting in Everus becoming an independent, publicly-traded company. The Company's board of directors approved the distribution of all the outstanding shares of Everus common stock to the Company's stockholders. Stockholders of the Company received one share of Everus common stock for every four shares of the Company's common stock held as of the close of business on October 21, 2024, the record date for the distribution. The separation of Everus was a tax-free spinoff transaction to the Company's stockholders for U.S. federal income tax purposes, except for cash received in lieu of fractional shares. The Company's consolidated financial statements and accompanying notes for the current and prior periods have been restated to present the results of operations and the assets and liabilities of Knife River and Everus as discontinued operations, other than certain corporate overhead costs of the Company historically allocated to Knife River and Everus, which are reflected in Other. Also included in discontinued operations in the Consolidated Statements of Income are the supporting activities of Fidelity and certain interest expense related to financing activity associated with the Knife River and Everus separations. The assets and liabilities of the Company's discontinued operations are included in current assets of discontinued operations, noncurrent assets of discontinued operations, current liabilities of discontinued operations and noncurrent liabilities of discontinued operations on the Consolidated Balance Sheets. Unless otherwise indicated, the amounts presented in the accompanying notes to the consolidated financial statements relate to the Company's continuing operations. For more information on discontinued operations, see Note 3. Additionally, certain amounts recorded in prior year financial statements have been reclassified to conform to the current year presentation. The Company has reclassified $26.9 million and $27.4 million of transmission-related expenses from operation and maintenance to electric fuel and purchased power for the years ended December 31, 2023 and 2022, respectively, in the Consolidated Statements of Income. These transmission-related expenses are an integral component of the cost of electricity sold to customers and therefore, more appropriately reflected in electric fuel and purchased power than operation and maintenance expense. These reclassifications had no effect on previously reported results of operations or cash flows. Management has also evaluated the impact of events occurring after December 31, 2024, up to the date of issuance of these consolidated financial statements on February 20, 2025, that would require recognition or disclosure in the financial statements. Principles of consolidation The consolidated financial statements were prepared in accordance with GAAP and include the accounts of the Company and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation, except for certain transactions related to regulated operations in accordance with GAAP. For more information on intercompany revenues, see Note 17. The statements also include the Company's ownership interests in the assets, liabilities and expenses of jointly owned electric transmission and generating facilities. See Note 19 for additional information. Use of estimates

Significant Accounting Policies

Significant Accounting Policies	12 Months Ended
	Dec. 31, 2024
Accounting Policies [Abstract]
Significant Accounting Policies	Significant Accounting Policies New accounting standards The following table provides a brief description of the accounting pronouncements applicable to the Company and the potential impact on its financial statements and/or disclosures: Standard Description Effective date Impact on financial statements/disclosures Recently adopted accounting standards ASU 2022-06 - Reference Rate Reform: Deferral of Sunset Date In December 2022, the FASB included a sunset provision within ASC 848 based on expectations of when LIBOR would cease being published. At the time ASU 2020-04 was issued, the UK Financial Conduct Authority had established its intent to cease overnight tenors of LIBOR after December 31, 2021. In March 2021, the UK Financial Conduct Authority announced that the intended cessation date of the overnight tenors of LIBOR would be June 30, 2023 which is beyond the current sunset date of ASC 848. The amendments in this Update defer the sunset date of ASC 848 from December 31, 2022 to December 31, 2024, after which entities will no longer be permitted to apply the relief in ASC 848. December 31, 2024 The Company has updated its credit agreements to include language regarding the successor or alternate rate to LIBOR. The Company did not have a material impact on its results of operations, financial position, cash flows or disclosures. ASU 2023-07 Segment Reporting - Improvements to Reportable Segment Disclosures In November 2023, the FASB issued guidance on improving financial reporting by requiring disclosure of incremental segment information, primarily through enhanced disclosures about significant segment expenses, on an annual and interim basis for all public entities to enable investors to develop more decision-useful financial analyses. December 31, 2024 The Company identified and updated disclosures to ensure compliance with the new guidance. See Note 17. Recently issued accounting standards not yet adopted ASU 2023-09 Income Taxes - Improvements to Income Tax Disclosures an Amendment, December 2023 In December 2023, the FASB issued guidance to address investors requests for more transparency about income tax information through improvements to income tax disclosures primarily related to the rate reconciliation and income taxes paid information and effectiveness of income tax disclosures. Effective for annual reporting periods beginning after 2024 on a prospective basis. The Company is currently evaluating the impact the guidance will have on its disclosures for the year ended December 31, 2025. ASU 2024-01 Compensation - Stock Compensation In March 2024, the FASB issued Improvements to GAAP through an example to demonstrate application of the scope of paragraph 718-10-15-3 to determine whether profits interest and similar awards should be accounted in Compensation - Stock Compensation. Effective for fiscal year beginning after December 15, 2024. The Company is currently evaluating the impact the guidance will have on its disclosures for the year ended December 31, 2025. ASU 2024-03 Disaggregation of Income Statement Expenses In November 2024, the FASB issued guidance to improve the disclosures about a public business entity's expenses and address requests from investors for more detailed information about the types of expenses (including purchases of inventory, employee compensation, depreciation, amortization, and depletion) in commonly presented expense captions (such as cost of sales, selling, general, and administrative; and research and development). Effective for annual reporting periods beginning after December 15, 2026, and interim reporting periods beginning after December 15, 2027. The Company is currently evaluating the impact the guidance will have on its disclosures for the year ended December 31, 2027. Cash, cash equivalents and restricted cash The Company considers all highly liquid investments purchased with an original maturity of three months or less to be cash equivalents. Restricted cash represents deposits held by the Company’s captive insurance company that is required by state insurance regulations to remain in the captive insurance company. The Company had restricted cash of $16.7 million and $13.2 million at December 31, 2024 and 2023, respectively. Revenue recognition Revenue is recognized when a performance obligation is satisfied by transferring control over a product or service to a customer. Revenue is measured based on consideration specified in a contract with a customer and excludes any sales incentives and amounts collected on behalf of third parties. The Company is considered an agent for certain taxes collected from customers. As such, the Company presents revenues net of these taxes at the time of sale to be remitted to governmental authorities, including sales and use taxes. The electric and natural gas distribution segments generate revenue from the sales of electric and natural gas products and services, which includes retail and transportation services. These segments establish a customer's retail or transportation service account based on the customer's application/contract for service, which indicates approval of a contract for service. The contract identifies an obligation to provide service in exchange for delivering or standing ready to deliver the identified commodity; and the customer is obligated to pay for the service as provided in the applicable tariff. The product sales are based on a fixed rate that includes a base and per-unit rate, which are included in approved tariffs as determined by state or federal regulatory agencies. The quantity of the commodity consumed or transported determines the total per-unit revenue. The service provided, along with the product consumed or transported, are a single performance obligation because both are required in combination to successfully transfer the contracted product or service to the customer. Revenues are recognized over time as customers receive and consume the products and services. The method of measuring progress toward the completion of the single performance obligation is on a per-unit output method basis, with revenue recognized based on the direct measurement of the value to the customer of the goods or services transferred to date. For contracts governed by the Company’s utility tariffs, amounts are billed monthly with the amount due between 15 and 22 days of receipt of the invoice depending on the applicable state’s tariff. For other contracts not governed by tariff, payment terms are net 30 days. At this time, the segment has no material obligations for returns, refunds or other similar obligations. The pipeline segment generates revenue from providing natural gas transportation and underground storage services, as well as other energy-related services to both third parties and internal customers, largely the natural gas distribution segment. The pipeline segment establishes a contract with a customer based upon the customer’s request for firm or interruptible natural gas transportation or storage service(s). The contract identifies an obligation for the segment to provide the requested service(s) in exchange for consideration from the customer over a specified term. Depending on the type of service(s) requested and contracted, the service provided may include transporting or storing an identified quantity of natural gas and/or standing ready to deliver or store an identified quantity of natural gas. Natural gas transportation and storage revenues are based on fixed rates, which may include reservation fees and/or per-unit commodity rates. The services provided by the segment are generally treated as single performance obligations satisfied over time simultaneous to when the service is provided and revenue is recognized. Rates for the segment’s regulated services are based on its FERC approved tariff or customer negotiated rates, and rates for its non-regulated services are negotiated with its customers and set forth in the contract. For contracts governed by the company’s tariff, amounts are billed on or before the ninth business day of the following month and the amount is due within 12 days of receipt of the invoice. For other contracts not governed by the tariff, payment terms are net 30 days. At this time, the segment has no material obligations for returns, refunds or other similar obligations. The Company recognizes all other revenues when services are rendered or goods are delivered. Legal costs The Company generally expenses external legal fees as they are incurred unless it has specific circumstances to defer, such as probable recovery in a rate proceeding. Receivables and allowance for expected credit losses Receivables consist primarily of trade receivables from the sale of goods and services net of expected credit losses. The Company's trade receivables are all due in 12 months or less. The total balance of receivables past due 90 days or more was $3.6 million and $3.7 million at December 31, 2024 and 2023, respectively. The Company's expected credit losses are determined through a review using historical credit loss experience, changes in asset specific characteristics, current conditions and reasonable and supportable future forecasts, among other specific account data, and is performed at least quarterly. The Company develops and documents its methodology to determine its allowance for expected credit losses at each of its reportable business segments. Risk characteristics used by the business segments may include customer mix, knowledge of customers and general economic conditions of the various local economies, among others. Specific account balances are written off when management determines the amounts to be uncollectible. Management has reviewed the balance reserved through the allowance for expected credit losses and believes it is reasonable. Details of the Company's expected credit losses were as follows: Electric Natural gas Pipeline Total (In thousands) At December 31, 2022 $ 375 $ 1,615 $ 2 $ 1,992 Current expected credit loss provision 1,645 5,777 — 7,422 Less write-offs charged against the allowance 1,994 7,355 2 9,351 Credit loss recoveries collected 388 1,152 — 1,540 At December 31, 2023 414 1,189 — 1,603 Current expected credit loss provision 1,891 4,667 — 6,558 Less write-offs charged against the allowance 2,218 5,709 — 7,927 Credit loss recoveries collected 386 1,219 — 1,605 At December 31, 2024 $ 473 $ 1,366 $ — $ 1,839 Receivables also consist of accrued unbilled revenue representing revenues recognized in excess of amounts billed. Accrued unbilled revenue at MDU Energy Capital was $143.2 million and $132.0 million at December 31, 2024 and 2023, respectively. Inventories and natural gas in storage Natural gas in storage is generally valued at lower of cost or market using the last-in, first-out method or lower of cost or net realizable value using the average cost or first-in, first-out method. The majority of all other inventories are valued at the lower of cost or net realizable value using the average cost method. The portion of the cost of natural gas in storage expected to be used within 12 months was included in inventories. Inventories at December 31 consisted of: 2024 2023 (In thousands) Natural gas in storage (current) $ 40,073 $ 39,377 Fuel stock 4,867 5,307 Total $ 44,940 $ 44,684 The remainder of natural gas in storage, which largely represents the cost of gas required to maintain pressure levels for normal operating purposes, was included in noncurrent assets - other and was $48.5 million at both December 31, 2024 and 2023, respectively. Property, plant and equipment Additions to property, plant and equipment are recorded at cost. When regulated assets are retired, or otherwise disposed of in the ordinary course of business, the original cost of the asset is charged to accumulated depreciation. With respect to the retirement or disposal of all other assets, the resulting gains or losses are recognized as a component of income. The Company is permitted to capitalize AFUDC on regulated construction projects and to include such amounts in rate base when the related facilities are placed in service. In addition, the Company capitalizes interest, when applicable, on certain contracting services projects associated with its other operations. The amount of AFUDC for the years ended December 31 was as follows: 2024 2023 2022 (In thousands) AFUDC - borrowed $ 10,964 $ 10,035 $ 2,236 AFUDC - equity $ 2,251 $ 1,894 $ 2,165 Generally, property, plant and equipment are depreciated on a straight-line basis over the average useful lives of the assets. The Company collects removal costs for certain plant assets in regulated utility rates. These amounts are recorded as regulatory liabilities on the Consolidated Balance Sheets. Impairment of long-lived assets, excluding goodwill The Company reviews the carrying values of its long-lived assets, whenever events or changes in circumstances indicate that such carrying values may not be recoverable. The Company tests long-lived assets for impairment at a level significantly lower than that of goodwill impairment testing. Long-lived assets or groups of assets that are evaluated for impairment at the lowest level of largely independent identifiable cash flows at an individual operation or group of operations collectively serving a local market. The determination of whether an impairment has occurred is based on an estimate of undiscounted future cash flows attributable to the assets, compared to the carrying value of the assets. If impairment has occurred, the amount of the impairment recognized is determined by estimating the fair value of the assets and recording a loss if the carrying value is greater than the fair value. The impairments are recorded in operation and maintenance expense on the Consolidated Statements of Income. No impairment losses were recorded in 2024, 2023 or 2022. Unforeseen events and changes in circumstances could require the recognition of impairment losses at some future date. Regulatory assets and liabilities The Company is subject to various state and federal agency regulations. The accounting policies followed by the Company are generally subject to the Uniform System of Accounts of the FERC as well as the provisions of ASC 980 - Regulated Operations . These accounting policies differ in some respects from those used by the Company's non-regulated businesses. The Company accounts for certain income and expense items under the provisions of regulatory accounting, which requires the Company to defer as regulatory assets or liabilities certain items that would have otherwise been reflected as expense or income, respectively. The Company records regulatory assets or liabilities at the time the Company determines the amounts to be recoverable in current or future rates. Regulatory assets and liabilities are being amortized consistently with the regulatory treatment established by the FERC and the applicable state public service commission. See Note 6 for more information regarding the nature and amounts of these regulatory deferrals. Goodwill Goodwill represents the excess of the purchase price over the fair value of identifiable net tangible and intangible assets acquired in a business combination. Goodwill is required to be tested for impairment annually, which the Company completes in the fourth quarter, or more frequently if events or changes in circumstances indicate that goodwill may be impaired. The Company has determined that the reporting units for its goodwill impairment test are its operating segments, or components of an operating segment, that constitute a business for which discrete financial information is available and for which segment management regularly reviews the operating results. As of December 31, 2024, the only operating segment with goodwill was the natural gas distribution segment. For more information on the Company's operating segments, see Note 17. Goodwill impairment, if any, is measured by comparing the fair value of each reporting unit to its carrying value. If the fair value of a reporting unit exceeds its carrying value, the goodwill of the reporting unit is not impaired. If the carrying value of a reporting unit exceeds its fair value, the Company must record an impairment loss for the amount that the carrying value of the reporting unit, including goodwill, exceeds the fair value of the reporting unit. For the years ended December 31, 2024, 2023 and 2022, there were no impairment losses recorded. Investments The Company's investments include the cash surrender value of life insurance policies, insurance contracts, mortgage-backed securities and U.S. Treasury securities. The Company measures its investment in the insurance contracts at fair value with any unrealized gains and losses recorded on the Consolidated Statements of Income. The Company has not elected the fair value option for its mortgage-backed securities and U.S. Treasury securities and, as a result, the unrealized gains and losses on these investments are recorded in accumulated other comprehensive loss. For more information, see Notes 9 and 18. Variable interest entities The Company evaluates its arrangements and contracts with other entities to determine if they are VIEs and if so, if the Company is the primary beneficiary. GAAP provides a framework for identifying VIEs and determining when a company should include the assets, liabilities, noncontrolling interest and results of activities of a VIE in its consolidated financial statements. A VIE should be consolidated if a party with an ownership, contractual or other financial interest in the VIE (a variable interest holder) has the power to direct the VIE's most significant activities and the obligation to absorb losses or right to receive benefits of the VIE that could be significant to the VIE. A variable interest holder that consolidates the VIE is called the primary beneficiary. Upon consolidation, the primary beneficiary generally must initially record all of the VIE's assets, liabilities and noncontrolling interests at fair value and subsequently account for the VIE as if it were consolidated. The Company's evaluation of whether it qualifies as the primary beneficiary of a VIE involves significant judgments, estimates and assumptions and includes a qualitative analysis of the activities that most significantly impact the VIE's economic performance and whether the Company has the power to direct those activities, the design of the entity, the rights of the parties and the purpose of the arrangement. Derivative instruments The Company enters into commodity price derivative contracts in order to minimize the price volatility associated with customer natural gas costs at its natural gas distribution segment. These derivatives are not designated as hedging instruments and are recorded in the Consolidated Balance Sheets at fair value. Changes in the fair value of these derivatives along with any contract settlements are recorded each period in regulatory assets or liabilities in accordance with regulatory accounting. The Company does not enter into any derivatives for trading or other speculative purposes. The Company did not have any material commodity price derivative contracts at December 31, 2024 or 2023. Leases Lease liabilities and their corresponding right-of-use assets are recorded based on the present value of lease payments over the expected lease term. The Company recognizes leases with an original lease term of 12 months or less in income on a straight-line basis over the term of the lease and does not recognize a corresponding right-of-use asset or lease liability. The Company determines the lease term based on the non-cancelable and cancelable periods in each contract. The non-cancelable period consists of the term of the contract that is legally enforceable and cannot be canceled by either party without incurring a significant penalty. The cancelable period is determined by various factors that are based on who has the right to cancel a contract. If only the lessor has the right to cancel the contract, the Company will assume the contract will continue. If the lessee is the only party that has the right to cancel the contract, the Company looks to asset, entity and market-based factors. If both the lessor and the lessee have the right to cancel the contract, the Company assumes the contract will not continue. The discount rate used to calculate the present value of the lease liabilities is based upon the implied rate within each contract. If the rate is unknown or cannot be determined, the Company uses an incremental borrowing rate, which is determined by the length of the contract, asset class and the Company's borrowing rates, as of the commencement date of the contract. Asset retirement obligations The Company records the fair value of a liability for an asset retirement obligation in the period in which it is incurred. When the liability is initially recorded, the Company capitalizes a cost by increasing the carrying amount of the related long-lived asset. Over time, the liability is accreted to its present value each period and the capitalized cost is depreciated over the useful life of the related asset. Upon settlement of the liability, the Company either settles the obligation for the recorded amount or incurs a gain or loss at its non-regulated operations or incurs a regulatory asset or liability at its regulated operations. Stock-based compensation The Company determines compensation expense for stock-based awards based on the estimated fair values at the grant date and recognizes the related compensation expense over the vesting period. The Company uses the straight-line amortization method to recognize compensation expense related to RSUs, which only has a service condition. This method recognizes stock compensation expense on a straight-line basis over the requisite service period for the entire award. The Company recognized compensation expense related to PSAs that vest based on performance metrics and service conditions on a straight-line basis over the service period. Inception-to-date expense was adjusted based upon the determination of the potential achievement of the performance target at each reporting date. The Company recognized compensation expense related to PSAs with market-based performance metrics on a straight-line basis over the requisite service period. Outstanding PSAs were converted to RSUs in connection with the completed separation of Knife River through the spinoff. The Company records the compensation expense for PSAs using an estimated forfeiture rate. The estimated forfeiture rate is calculated based on an average of actual historical forfeitures. The Company also performs an analysis of any known factors at the time of the calculation to identify any necessary adjustments to the average historical forfeiture rate. At the time actual forfeitures become more than estimated forfeitures, the Company records compensation expense using actual forfeitures. Earnings per share Basic earnings per share is computed by dividing net income by the weighted average number of shares of common stock outstanding during the year. Diluted earnings per share is computed by dividing net income by the total of the weighted average number of shares of common stock outstanding during the year, plus the effect of nonvested performance share awards and restricted stock units. Common stock outstanding includes issued shares less shares held in treasury. As a result of the 2023 Knife River separation, the Company retained legal ownership of 538,921 shares of the Company's common stock that were historically owned by a subsidiary of Knife River and recorded in Treasury stock at cost. Following the separation, the 538,921 treasury shares were retired. The 538,921 shares of treasury stock did not have an impact on weighted-average shares outstanding, as they were not outstanding prior to being retired. Net income was the same for both the basic and diluted earnings per share calculations. A reconciliation of the weighted average common shares outstanding used in the basic and diluted earnings per share calculations follows: 2024 2023 2022 (In thousands, except per share amounts) Weighted average common shares outstanding - basic 203,867 203,640 203,358 Effect of dilutive performance share awards 786 298 104 Weighted average common shares outstanding - diluted 204,653 203,938 203,462 Earnings per share - basic: Income from continuing operations $ .89 $ 1.62 $ .58 Discontinued operations, net of tax .49 .42 1.23 Earnings per share - basic $ 1.38 $ 2.04 $ 1.81 Earnings per share - diluted: Income from continuing operations $ .88 $ 1.62 $ .58 Discontinued operations, net of tax .49 .41 1.23 Earnings per share - diluted $ 1.37 $ 2.03 $ 1.81 Shares excluded from the calculation of diluted earnings per share — — 14 Dividends declared per common share $ .5100 $ .6950 $ .8750 Income taxes The Company provides deferred federal and state income taxes on all temporary differences between the book and tax basis of the Company's assets and liabilities by using enacted tax rates in effect for the year in which the differences are expected to reverse. The effect of a change in tax rates on deferred tax assets and liabilities is recognized in income in the period that includes the enactment date. Excess deferred income tax balances associated with the Company's rate-regulated activities have been recorded as regulatory liabilities. These regulatory liabilities are expected to be reflected as a reduction in future rates charged to customers in accordance with applicable regulatory procedures. The Company uses the deferral method of accounting for investment tax credits and amortizes the credits on regulated electric and natural gas distribution plant over various periods that conform to the ratemaking treatment prescribed by the applicable state public service commissions.

Discontinued Operations

Discontinued Operations	12 Months Ended
	Dec. 31, 2024
Discontinued Operations and Disposal Groups [Abstract]
Discontinued Operations	Discontinued Operations On May 31, 2023, the Company completed the separation of Knife River, its former construction materials and contracting segment, into a new independent publicly-traded company. The separation was achieved through the Company's pro-rata distribution of approximately 90 percent of the outstanding shares of Knife River to the Company's common stockholders. To effect the separation, the Company distributed to its stockholders one share of Knife River common stock for every four shares of the Company's common stock held on May 22, 2023, the record date for the distribution, with the Company retaining approximately 10 percent, or 5.7 million shares of Knife River common stock immediately following the separation. In November 2023, the Company completed the tax-free exchange of its retained shares and recognized a gain of $186.6 million, which was reflected in continuing operations because the Company did not have continuing significant involvement in Knife River. The separation of Knife River was a tax-free spinoff transaction to the Company's stockholders for U.S. federal income tax purposes, except for cash received in lieu of fractional shares. On October 31, 2024, the Company completed the separation of Everus, its former construction services segment, into a new independent, publicly-traded company. The Company's board of directors approved the distribution of all the outstanding shares of Everus common stock to the Company's stockholders. Stockholders of the Company received one share of Everus common stock for every four shares of the Company's common stock held as of the close of business on October 21, 2024, the record date for the distribution. The separation of Everus was a tax-free spinoff transaction to the Company's stockholders for U.S. federal income tax purposes, except for cash received in lieu of fractional shares. As a result of the separations, the historical results of operations are shown in discontinued operations, net of tax, except for allocated general corporate overhead costs of the Company, which did not meet the criteria for discontinued operations. The Company’s consolidated financial statements and accompanying notes for prior periods have been restated. For the comparative periods, Everus' operations are only reflected through October 2024 compared to the full year in 2023 and 2022 and Knife River's operations are only reflected through May 2023 compared to the full year in 2022. On April 25, 2023, Knife River issued $425.0 million of senior notes, pursuant to an indenture, due in 2031 to qualified institutional buyers. Knife River also entered into a new credit agreement which provided a revolving credit facility in an initial amount of up to $350.0 million and a senior secured term loan facility in an amount up to $275.0 million. The net proceeds from the notes offering, revolving credit facility and the term loan were used to repay $825.0 million of Knife River's intercompany obligations owed to Centennial. Centennial used the entirety of these proceeds from Knife River to repay a portion of its existing third-party indebtedness. As a result of the separation of Knife River, the Company retained legal ownership of 538,921 shares of the Company's common stock that were historically owned by a subsidiary of Knife River and recorded in Treasury stock at cost. Following the separation of Knife River, the 538,921 treasury shares were retired. The Company provided to Knife River and Knife River provided to the Company transition services in accordance with the transition services agreement entered into on May 31, 2023. For the twelve months ended December 31, 2024 and 2023, the Company received $1.5 million and $2.9 million, respectively; and paid $159,000 and $823,000, respectively, for these related activities. All transition services were completed as of October 2024. The Company provided and will provide to Everus and Everus provided and will provide to the Company transition services in accordance with the transition services agreement entered into on October 31, 2024. For the twelve months ended December 31, 2024, the Company received $727,000; and paid $47,000, for these related activities. The majority of the transition services are expected to be provided for a period of approximately eighteen months, however, no longer than two years after the separation. Separation related costs of $41.7 million, $58.6 million and $11.5 million net of tax, were incurred during the twelve months ended December 31, 2024, 2023 and 2022, respectively. Certain separation costs incurred are presented in discontinued operations, net of tax The Company had no assets or liabilities related to the discontinued operations of Knife River on its balance sheet as of December 31, 2024 and 2023. The carrying amounts of the major classes of assets and liabilities related to the discontinued operations of Everus included in the Company’s Consolidated Balance Sheet at December 31, 2023 were as follows: December 31, 2023 Assets (In Thousands) Current assets: Cash and cash equivalents $ 16,501 Receivables, net 692,629 Inventories 42,709 Prepayments and other current assets 17,651 Total current assets of discontinued operations 769,490 Noncurrent assets: Net property, plant and equipment 116,018 Goodwill 143,224 Other intangible assets, net 2,004 Investments 11,760 Operating lease right-of-use assets 53,232 Other 21,627 Total noncurrent assets of discontinued operations 347,865 Total assets of discontinued operations $ 1,117,355 Liabilities Current liabilities: Accounts payable $ 315,240 Taxes payable 8,557 Accrued compensation 44,721 Operating lease liabilities due within one year 21,143 Other accrued liabilities 53,619 Total current liabilities of discontinued operations 443,280 Noncurrent liabilities: Long-term debt 132,000 Deferred income taxes 6,212 Operating lease liabilities 32,504 Other 8,934 Total noncurrent liabilities of discontinued operations 179,650 Total liabilities of discontinued operations $ 622,930 The reconciliation of the major classes of income and expense constituting pretax income from discontinued operations to the after-tax income from discontinued operations on the Consolidated Statements of Income were as follows: 2024 2023 2022 (In thousands) Operating revenues $ 2,377,332 $ 3,589,251 $ 5,226,766 Operating expenses 2,241,162 3,422,393 4,853,408 Operating (loss) income 136,170 166,858 373,358 Other income (expense) 12,446 10,599 4,119 Interest expense 7,118 47,229 38,590 Income from discontinued operations before income taxes 141,498 130,228 338,887 Income taxes 41,463 45,638 88,650 Discontinued operations, net of tax $ 100,035 $ 84,590 $ 250,237

Revenue from Contracts with Cus

Revenue from Contracts with Customers	12 Months Ended
	Dec. 31, 2024
Revenue from Contract with Customer [Abstract]
Revenue from Contracts with Customers	Revenue from Contracts with Customers Revenue is recognized when a performance obligation is satisfied by transferring control over a product or service to a customer. Revenue is measured based on consideration specified in a contract with a customer and excludes any sales incentives and amounts collected on behalf of third parties. The Company is considered an agent for certain taxes collected from customers. As such, the Company presents revenues net of these taxes at the time of sale to be remitted to governmental authorities, including sales and use taxes. As part of the adoption of ASC 606 - Revenue from Contracts with Customers , the Company elected the practical expedient to recognize the incremental costs of obtaining a contract as an expense when incurred if the amortization period of the asset that the Company otherwise would have recognized is 12 months or less. Disaggregation In the following table, revenue is disaggregated by the type of customer or service provided. The Company believes this level of disaggregation best depicts how the nature, amount, timing and uncertainty of revenue and cash flows are affected by economic factors. The table also includes a reconciliation of the disaggregated revenue by reportable segments. For more information on the Company's business segments, see Note 17. Year ended December 31, 2024 Electric Natural gas distribution Pipeline Other Total (In thousands) Residential utility sales $ 140,054 $ 646,049 $ — $ — $ 786,103 Commercial utility sales 171,760 399,087 — — 570,847 Industrial utility sales 42,883 42,588 — — 85,471 Other utility sales 7,910 — — — 7,910 Natural gas transportation — 60,645 174,623 — 235,268 Natural gas storage — — 23,690 — 23,690 Other 59,288 40,703 13,139 195 113,325 Intersegment eliminations (72) (130) (69,222) (195) (69,619) Revenues from contracts with customers 421,823 1,188,942 142,230 — 1,752,995 Other revenues (7,417) 12,033 367 — 4,983 Total external operating revenues $ 414,406 $ 1,200,975 $ 142,597 $ — $ 1,757,978 Year ended December 31, 2023 Electric Natural gas distribution Pipeline Other Total (In thousands) Residential utility sales $ 136,274 $ 724,600 $ — $ — $ 860,874 Commercial utility sales 170,321 442,507 — — 612,828 Industrial utility sales 43,063 45,205 — — 88,268 Other utility sales 7,270 — — — 7,270 Natural gas transportation — 52,465 145,297 — 197,762 Natural gas storage — — 18,254 — 18,254 Other 54,508 15,141 13,874 119 83,642 Intersegment eliminations (138) (301) (62,533) (119) (63,091) Revenues from contracts with customers 411,298 1,279,617 114,892 — 1,805,807 Other revenues (10,261) 7,619 187 — (2,455) Total external operating revenues $ 401,037 $ 1,287,236 $ 115,079 $ — $ 1,803,352 Year ended December 31, 2022 Electric Natural gas distribution Pipeline Other Total (In thousands) Residential utility sales $ 138,634 $ 718,191 $ — $ — $ 856,825 Commercial utility sales 146,182 453,802 — — 599,984 Industrial utility sales 43,766 41,710 — — 85,476 Other utility sales 7,597 — — — 7,597 Natural gas transportation — 48,886 129,290 — 178,176 Natural gas storage — — 14,583 — 14,583 Other 45,608 13,617 11,450 86 70,761 Intersegment eliminations (58) (216) (58,884) (86) (59,244) Revenues from contracts with customers 381,729 1,275,990 96,439 — 1,754,158 Other revenues (4,714) (2,402) 256 — (6,860) Total external operating revenues $ 377,015 $ 1,273,588 $ 96,695 $ — $ 1,747,298 Remaining performance obligations The remaining performance obligations at the pipeline segment include firm transportation and storage contracts with fixed pricing and fixed volumes. The Company has applied the practical expedient that does not require additional disclosures for contracts with an original duration of less than 12 months to certain firm transportation and non-regulated contracts. The Company's firm transportation and storage contracts included in the remaining performance obligations have weighted average remaining durations of less than five years and one year, respectively. 12 months

Property, Plant and Equipment

Property, Plant and Equipment	12 Months Ended
	Dec. 31, 2024
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	Property, Plant and Equipment Property, plant and equipment at December 31 was as follows: 2024 2023 Weighted (Dollars in thousands, where applicable) Electric: Generation $ 1,014,906 $ 939,474 49 Distribution 546,121 521,215 47 Transmission 662,466 639,999 65 CWIP 81,316 115,103 0 Other 176,007 153,248 15 Natural gas distribution: Distribution 2,955,435 2,771,540 53 Transmission 146,710 115,057 56 Storage 43,700 42,654 37 General 229,034 215,572 13 CWIP 74,207 70,373 0 Other 282,007 246,991 15 Pipeline: Transmission 1,173,259 1,035,995 46 Storage 61,369 57,160 53 CWIP 29,629 57,038 0 Other 73,749 68,194 17 Other: Land and other 4,148 31,654 7 Less accumulated depreciation and amortization 2,209,771 2,076,375 Net property, plant and equipment $ 5,344,292 $ 5,004,892

Regulatory Assets and Liabiliti

Regulatory Assets and Liabilities	12 Months Ended
	Dec. 31, 2024
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Assets and Liabilities	Regulatory Assets and Liabilities The following table summarizes the individual components of unamortized regulatory assets and liabilities as of December 31: Estimated Recovery or Refund Period * 2024 2023 (In thousands) Regulatory assets: Current: Natural gas costs recoverable through rate adjustments Up to 1 year $ 91,091 $ 98,844 Environmental compliance programs Up to 1 year 76,964 5,525 Conservation programs Up to 1 year 19,123 14,425 Electric fuel and purchased power deferral Up to 1 year 9,662 33,918 Decoupling mechanisms Up to 1 year 6,767 — Cost recovery mechanisms Up to 1 year 5,114 9,153 Other Up to 1 year 6,715 10,627 215,436 172,492 Noncurrent: Pension and postretirement benefits ** 142,064 142,511 Cost recovery mechanisms Up to 24 years 76,542 85,944 Plant costs/asset retirement obligations Over plant lives 47,042 46,009 Manufactured gas plant site remediation - 27,964 26,127 Taxes recoverable from customers Over plant lives 12,221 12,249 Electric fuel and purchased power deferral Up to 2 years 4,349 — Covid-19 deferred costs - 4,167 2,746 Long-term debt refinancing costs Up to 36 years 2,011 2,600 Environmental compliance programs - — 66,806 Natural gas costs recoverable through rate adjustments Up to 2 years — 55,493 Other Up to 14 years 5,990 6,614 322,350 447,099 Total regulatory assets $ 537,786 $ 619,591 Regulatory liabilities: Current: Environmental compliance Up to 1 year $ 72,387 $ — Natural gas costs refundable through rate adjustments Up to 1 year 45,427 43,161 Margin sharing Up to 1 year 4,156 5,243 Provision for rate refund Up to 1 year 3,677 6,866 Taxes refundable to customers Up to 1 year 2,163 2,149 Conservation programs Up to 1 year 2,082 2,130 Cost recovery mechanisms Up to 1 year 1,720 6,284 Other Up to 1 year 5,555 4,928 137,167 70,761 Noncurrent: Plant removal and decommissioning costs Over plant lives 217,603 220,147 Taxes refundable to customers Over plant lives 185,402 193,578 Cost recovery mechanisms Up to 17 years 30,354 21,791 Accumulated deferred investment tax credit Over plant lives 18,788 15,740 Pension and postretirement benefits ** 4,862 6,044 Environmental compliance programs - — 61,941 Other Up to 13 years 2,161 1,809 459,170 521,050 Total regulatory liabilities $ 596,337 $ 591,811 Net regulatory position $ (58,551) $ 27,780 * Estimated recovery or refund period for amounts currently being recovered or refunded in rates to customers. ** Recovered as expense is incurred or cash contributions are made. As of December 31, 2024 and 2023, approximately $181.2 million and $194.3 million, respectively, of regulatory assets were not earning a rate of return but are expected to be recovered from customers in future rates. These assets are largely comprised of the unfunded portion of pension and postretirement benefits, asset retirement obligations, certain pipeline integrity costs and the estimated future cost of manufactured gas plant site remediation. The Company is subject to environmental compliance regulations in certain states which require natural gas distribution companies to reduce overall GHG emissions to certain thresholds as established by each applicable state. Compliance with these standards may be achieved through increased energy efficiency and conservation measures, purchased emission allowances and offsets and purchases of low carbon fuels. Emission allowances are allocated by the respective states to the Company at no cost, of which a portion is required to be sold at auction. The compliance costs for these regulations and the revenues from the sale of the allocated emissions allowances are passed through to customers in rates and the Company has, accordingly, deferred the environmental compliance costs as a regulatory asset and proceeds from the sale of allowances as a regulatory liability. For a discussion of the Company's most recent cases by jurisdiction, see Note 20. If, for any reason, the Company's regulated businesses cease to meet the criteria for application of regulatory accounting for all or part of their operations, the regulatory assets and liabilities relating to those portions ceasing to meet such criteria would be written off and included in the statement of income or accumulated other comprehensive loss in the period in which the discontinuance of regulatory accounting occurs.

Environmental Allowances and Ob

Environmental Allowances and Obligations	12 Months Ended
	Dec. 31, 2024
Environmental Remediation Obligations [Abstract]
Environmental Allowance and Obligations	Environmental Allowances and Obligations Beginning in 2023, the Company's natural gas distribution segment acquires environmental allowances as part of its requirement to comply with environmental regulations in certain states. Allowances are allocated by the respective states to the Company at no cost and additional allowances are required to be purchased as needed based on the requirements in the respective states. The segment records purchased and allocated environmental allowances at weighted average cost under the inventory method of accounting. Environmental allowances are included in Prepayments and other current assets and noncurrent assets - Other on the Consolidated Balance Sheets. Environmental compliance obligations, which are based on GHG emissions, are measured at the carrying value of environmental allowances held plus the estimated value of additional allowances necessary to satisfy the compliance obligation. Environmental compliance obligations are included in current liabilities - Other accrued liabilities and noncurrent liabilities - Other on the Consolidated Balance Sheets. The Company recognizes revenue from the sale of emissions allowances allocated under the environmental programs when the allowances are sold at auction. The revenues associated with the sale of these allowances are deferred as a component of the respective jurisdiction’s regulatory liability for environmental compliance. As environmental allowances are surrendered, the segment reduces the associated environmental compliance assets and liabilities from the Consolidated Balance Sheets. The expenses and revenues associated with the Company’s environmental allowances and obligations are deferred as regulatory assets and liabilities and recognized as a component of purchased natural gas sold as recovered in customer rates. For more information on the Company’s regulatory assets and liabilities, see Note 6.

Goodwill

Goodwill	12 Months Ended
	Dec. 31, 2024
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	Goodwill The carrying amount of goodwill at the natural gas distribution segment, which remained unchanged, was $345.7 million, respectively, at both December 31, 2024 and 2023. No impairments of goodwill have been recorded in these periods.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2024
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability (an exit price) in an orderly transaction between market participants at the measurement date. The fair value ASC establishes a hierarchy for grouping assets and liabilities, based on the significance of inputs. The estimated fair values of the Company's assets and liabilities measured on a recurring basis are determined using the market approach. The Company measures its investments in certain fixed-income and equity securities at fair value with changes in fair value recognized in income. The Company anticipates using these investments, which consist of insurance contracts, to satisfy its obligations under its unfunded, nonqualified defined benefit and defined contribution plans for executive officers and certain key management employees and invests in these fixed-income and equity securities for the purpose of earning investment returns and capital appreciation. These investments, which totaled $59.3 million and $62.9 million at December 31, 2024 and 2023, respectively, are classified as investments on the Consolidated Balance Sheets. The net unrealized gain on these investments for the year ended December 31, 2024 and 2023, was $5.9 million and $7.4 million, respectively. The net unrealized loss on these investments for the year ended December 31, 2022 was $11.2 million. The change in fair value, which is considered part of the cost of the plan, is classified in Other income on the Consolidated Statements of Income. In the first quarter of 2024 and the fourth quarter of 2023, the Company withdrew $9.0 million and $20.0 million, respectively, of its cost basis, which reduced Investments on the Consolidated Balance Sheets. The Company did not elect the fair value option, which records gains and losses in income, for its available-for-sale securities, which include mortgage-backed securities and U.S. Treasury securities. These available-for-sale securities are recorded at fair value and are classified as Investments on the Consolidated Balance Sheets. Unrealized gains or losses are recorded in Accumulated other comprehensive loss on the Consolidated Balance Sheets. Details of available-for-sale securities were as follows: December 31, 2024 Cost Gross Gross Fair Value (In thousands) Mortgage-backed securities $ 7,933 $ 4 $ 383 $ 7,554 U.S. Treasury securities 3,945 80 1 4,024 Total $ 11,878 $ 84 $ 384 $ 11,578 December 31, 2023 Cost Gross Gross Fair Value (In thousands) Mortgage-backed securities $ 8,234 $ 17 $ 470 $ 7,781 U.S. Treasury securities 3,521 28 8 3,541 Total $ 11,755 $ 45 $ 478 $ 11,322 The Company's assets measured at fair value on a recurring basis were as follows: Fair Value Measurements at December 31, 2024, Using Quoted Prices Significant Significant Balance at December 31, 2024 (In thousands) Assets: Money market funds $ — $ 12,879 $ — $ 12,879 Insurance contracts* — 59,282 — 59,282 Available-for-sale securities: Mortgage-backed securities — 7,554 — 7,554 U.S. Treasury securities — 4,024 — 4,024 Total assets measured at fair value $ — $ 83,739 $ — $ 83,739 * The insurance contracts invest approximately 58 percent in fixed-income investments, 17 percent in common stock of large-cap companies, 8 percent in target date investments, 8 percent in common stock of mid-cap companies, 4 percent in common stock of small-cap companies, 4 percent in cash equivalents, and 1 percent in international investments. Fair Value Measurements at December 31, 2023, Using Quoted Prices Significant Significant Balance at December 31, 2023 (In thousands) Assets: Money market funds $ — $ 6,409 $ — $ 6,409 Insurance contracts* — 62,936 — 62,936 Available-for-sale securities: Mortgage-backed securities — 7,781 — 7,781 U.S. Treasury securities — 3,541 — 3,541 Total assets measured at fair value $ — $ 80,667 $ — $ 80,667 * The insurance contracts invest approximately 60 percent in fixed-income investments, 15 percent in common stock of large-cap companies, 8 percent in target date investments, 7 percent in common stock of mid-cap companies, 5 percent in common stock of small-cap companies, 3 percent in cash equivalents, 1 percent in high yield investments, and 1 percent in international investments. The Company's money market funds are valued at the net asset value of shares held at the end of the period, based on published market quotations on active markets, or using other known sources including pricing from outside sources. The estimated fair value of the Company's mortgage-backed securities and U.S. Treasury securities are based on comparable market transactions, other observable inputs or other sources, including pricing from outside sources. The estimated fair value of the Company's insurance contracts are based on contractual cash surrender values that are determined primarily by investments in managed separate accounts of the insurer. These amounts approximate fair value. The managed separate accounts are valued based on other observable inputs or corroborated market data. Though the Company believes the methods used to estimate fair value are consistent with those used by other market participants, the use of other methods or assumptions could result in a different estimate of fair value. The Company applies the provisions of the fair value measurement standard to its nonrecurring, non-financial measurements, including long-lived asset impairments. These assets are not measured at fair value on an ongoing basis but are subject to fair value adjustments only in certain circumstances. The Company reviews the carrying value of its long-lived assets, excluding goodwill, whenever events or changes in circumstances indicate that such carrying amounts may not be recoverable. The Company's long-term debt is not measured at fair value on the Consolidated Balance Sheets and the fair value is being provided for disclosure purposes only. The fair value was categorized as Level 2 in the fair value hierarchy and was based on discounted future cash flows using current market interest rates. The estimated fair value of the Company's Level 2 long-term debt at December 31 was as follows: 2024 2023 (In thousands) Carrying Amount $ 2,292,610 $ 2,166,223 Fair Value $ 1,963,396 $ 1,914,039 The carrying amounts of the Company's remaining financial instruments included in current assets and current liabilities approximate their fair values.

Debt

Debt	12 Months Ended
	Dec. 31, 2024
Debt Disclosure [Abstract]
Debt	Debt Due to the Knife River separation, Centennial repaid all of its outstanding debt in the second quarter of 2023, which was funded by the Knife River repayment and the Company entering into various new debt instruments. Refer to Note 3 for additional information related to the repayment of debt associated with the Knife River separation. Certain debt instruments of the Company and its subsidiaries contain restrictive and financial covenants and cross-default provisions. In order to borrow under the respective debt agreements, the Company and its subsidiaries must be in compliance with the applicable covenants and certain other conditions, all of which the Company and its subsidiaries, as applicable, were in compliance with at December 31, 2024. In the event the Company or its subsidiaries do not comply with the applicable covenants and other conditions, alternative sources of funding may need to be pursued. The following table summarizes the outstanding revolving credit facilities of the Company and its subsidiaries: Company Facility Facility Amount Outstanding at December 31, 2024 Amount Outstanding at December 31, 2023 Letters of Credit at December 31, 2024 Expiration (In millions) Montana-Dakota Utilities Co. Commercial paper/Revolving credit agreement (a) $ 200.0 $ 81.4 $ 144.2 $ — 10/18/28 Cascade Natural Gas Corporation Revolving credit agreement $ 175.0 (b) $ 64.6 $ 15.4 $ 2.2 (c) 6/20/29 Intermountain Gas Company Revolving credit agreement $ 175.0 (b) $ 105.1 $ 30.7 $ — 6/20/29 MDU Resources Group, Inc. Revolving credit agreement $ 200.0 (d) $ — $ — $ 12.1 (c) 5/31/28 (a) The commercial paper program is supported by a revolving credit agreement with various banks (provisions allow for increased borrowings, at the option of Montana-Dakota on stated conditions, up to a maximum of $250.0 million). At December 31, 2024 and 2023, there were no amounts outstanding under the revolving credit agreement. (b) Certain provisions allow for increased borrowings, up to a maximum of $225.0 million. (c) Outstanding letter(s) of credit reduce the amount available under the credit agreement. (d) Certain provisions allow for increased borrowings, up to a maximum of $250.0 million. Montana-Dakota's commercial paper program is supported by a revolving credit agreement. While the amount of commercial paper outstanding does not reduce available capacity under the revolving credit agreement, Montana-Dakota does not issue commercial paper in an aggregate amount exceeding the available capacity under the credit agreement. The commercial paper and revolving credit agreement borrowings may vary during the period, largely the result of fluctuations in working capital requirements due to the seasonality of certain operations of Montana-Dakota. Short-term debt Cascade On January 20, 2023, Cascade entered into a $150.0 million term loan agreement with a SOFR-based variable interest rate and a maturity date of January 19, 2024. On December 5, 2023, Cascade paid down $100.0 million of the outstanding balance. On January 19, 2024, Cascade made the final $50.0 million repayment on the term loan agreement. Intermountain On January 20, 2023, Intermountain entered into a $125.0 million term loan agreement with a SOFR-based variable interest rate and a maturity date of January 19, 2024. In March, April and May 2023, Intermountain paid down $20.0 million, $30.0 million, and $30.0 million, respectively, of the outstanding balance. On January 19, 2024 Intermountain made the final $45.0 million repayment on the term loan agreement. MDU Resources Group, Inc. On May 31, 2023, the Company entered into a $150.0 million revolving credit agreement with a SOFR-based variable interest rate and a maturity date of May 29, 2024. At December 31, 2023, the Company had no amount outstanding, which remained that way until this agreement matured and subsequently terminated in May 2024. Long-term debt Long-term Debt Outstanding Long-term debt outstanding was as follows: Weighted Average Interest Rate at December 31, 2024 2024 2023 (In thousands) Senior notes due on dates ranging from August 23, 2025 to June 15, 2062 4.57 % $ 1,947,000 $ 1,882,000 Credit agreements due on June 20, 2029 5.79 % 169,700 46,100 Commercial paper supported by revolving credit agreement 4.76 % 81,400 144,200 Term loan agreements due on dates ranging from September 3, 2032 to April 1, 2039 4.44 % 65,600 64,300 Medium-term notes due on dates ranging from September 15, 2027 to March 16, 2029 7.32 % 35,000 35,000 Other notes due on dates ranging from May 31, 2028 to November 30, 2038 6.00 % 346 980 Less unamortized debt issuance costs 6,436 6,357 Total long-term debt 2,292,610 2,166,223 Less current maturities 161,700 61,319 Net long-term debt $ 2,130,910 $ 2,104,904 Montana-Dakota On October 18, 2023, Montana-Dakota amended and restated its revolving credit agreement to increase the borrowing capacity to $200.0 million and extend the maturity date to October 18, 2028. Montana-Dakota's revolving credit agreement supports its commercial paper program. Commercial paper borrowings under this agreement are classified as long-term debt as they are intended to be refinanced on a long-term basis through continued commercial paper borrowings. The credit agreement contains customary covenants and provisions, including covenants of Montana-Dakota not to permit, as of the end of any fiscal quarter, the ratio of funded debt to total capitalization (determined on a consolidated basis) to be greater than 65 percent. Other covenants include limitations on the sale of certain assets and on the making of certain loans and investments. On July 11, 2024, Montana-Dakota issued $125.0 million of senior notes under a note purchase agreement with maturity dates ranging from July 11, 2039 to July 11, 2054, at a weighted average interest rate of 5.96 percent. The agreement contains customary covenants and provisions, including a covenant of Montana-Dakota not to permit, at any time, the ratio of total debt to capitalization to be greater than 65 percent. The covenants also include certain restrictions on the sale of certain assets, loans and investments. Montana-Dakota's ratio of total debt to total capitalization at December 31, 2024, was 48 percent. Cascade On June 20, 2024, Cascade amended and restated its revolving credit agreement to increase the borrowing capacity from $100.0 million to $175.0 million and extend the maturity date to June 20, 2029. Any borrowings under the revolving credit agreement are classified as long-term debt as they are intended to be refinanced on a long-term basis through continued borrowings. The credit agreement contains customary covenants and provisions, including a covenant of Cascade not to permit, at any time, the ratio of total debt to total capitalization to be greater than 65 percent. Other covenants include restrictions on the sale of certain assets, limitations on indebtedness and the making of certain investments. Cascade's ratio of total debt to total capitalization at December 31, 2024, was 50 percent. Intermountain On June 20, 2024, Intermountain amended and restated its revolving credit agreement to increase the borrowing capacity from $100.0 million to $175.0 million and extend the maturity date to June 20, 2029. Any borrowings under the revolving credit agreement are classified as long-term debt as they are intended to be refinanced on a long-term basis through continued borrowings. The credit agreement contains customary covenants and provisions, including a covenant of Intermountain not to permit, at any time, the ratio of total debt to total capitalization to be greater than 65 percent. Other covenants include restrictions on the sale of certain assets, limitations on indebtedness and the making of certain investments. Intermountain's ratio of total debt to total capitalization at December 31, 2024, was 60 percent. MDU Resources Group, Inc. On May 31, 2023, the Company entered into a $200.0 million revolving credit agreement with a SOFR-based variable interest rate and a maturity date of May 31, 2028. Any borrowings under the revolving credit agreement are classified as long-term debt as they are intended to be refinanced on a long-term basis through continued borrowings. The credit agreement contains customary covenants and provisions, including a covenant of the Company not to permit, at any time, the ratio of total debt to total capitalization to be greater than 65 percent. The covenants also include certain restrictions on the sale of certain assets, loans and investments. On May 31, 2023, the Company entered into a $375.0 million term loan agreement with a SOFR-based variable interest rate and a maturity date of May 31, 2025. On November 15, 2023, the Company paid down $185.0 million of the term loan agreement. On November 1, 2024, the Company repaid its remaining outstanding balance of $190.0 million and the term loan agreement subsequently terminated. The Company's repayment was funded by the Everus repayment of debt in connection with the separation. Refer to Note 3 for additional information related to the repayment of debt associated with the Everus separation. The Company's ratio of total debt to total capitalization at December 31, 2024, was 46 percent. WBI Energy Transmission WBI Energy Transmission has a $350.0 million uncommitted note purchase and private shelf agreement with an expiration date of December 22, 2025. WBI Energy Transmission had $235.0 million of notes outstanding at December 31, 2024, which reduced the remaining capacity under this uncommitted private shelf agreement to $115.0 million. This agreement contains customary covenants and provisions, including a covenant of WBI Energy Transmission not to permit, as of the end of any fiscal quarter, the ratio of total debt to total capitalization to be greater than 55 percent. Other covenants include a limitation on priority debt, restrictions on the sale of certain assets and the making of certain investments. On April 1, 2024, WBI Energy Transmission entered into a $60.0 million term loan agreement with an interest rate of 4.52 percent and a maturity date of April 1, 2039, with the principal to be repaid in equal annual installments of $4.0 million each, beginning March 2025 and continuing through the maturity date. The agreement contains customary covenants and provisions, including a covenant of WBI Energy Transmission not to permit, at any time, the ratio of total debt to total capitalization to be greater than 65 percent. The covenants also include certain restrictions on the sale of certain assets, loans and investments. WBI Energy Transmission's ratio of total debt to total capitalization at December 31, 2024, was 40 percent. Schedule of Debt Maturities Long-term debt maturities, which excludes unamortized debt issuance costs and discount, for the five years and thereafter following December 31, 2024, were as follows: 2025 2026 2027 2028 2029 Thereafter (In thousands) Long-term debt maturities $ 161,700 $ 144,700 $ 24,700 $ 161,100 $ 244,400 $ 1,562,446

Asset Retirement Obligations

Asset Retirement Obligations	12 Months Ended
	Dec. 31, 2024
Asset Retirement Obligation [Abstract]
Asset Retirement Obligations	Asset Retirement Obligations The Company records obligations related to retirement costs of natural gas distribution lines, natural gas transmission lines, natural gas storage wells, decommissioning of certain electric generating facilities, special handling and disposal of hazardous materials at certain electric generating facilities, natural gas distribution facilities and buildings, and certain other obligations as asset retirement obligations. A reconciliation of the Company's liability, which the current portion is included in other accrued liabilities on the Consolidated Balance Sheets, for the years ended December 31 was as follows: 2024 2023 (In thousands) Balance at beginning of year $ 385,154 $ 373,147 Liabilities incurred 2,721 533 Liabilities settled (5,271) (6,633) Accretion expense* 19,655 18,894 Revisions in estimates 4,388 (787) Balance at end of year $ 406,647 $ 385,154 * Includes $19.6 million and $18.9 million in 2024 and 2023, respectively, recorded to regulatory assets. The 2024 revisions in estimates consist principally of updated asset retirement obligation costs resulting from decommissioning studies performed for electric generating facilities at the electric segment. The Company believes that largely all expenses related to asset retirement obligations at the Company's regulated operations will be recovered in rates over time and, accordingly, defers such expenses as regulatory assets. For more information on the Company's regulatory assets and liabilities, see Note 6.

Equity

Equity	12 Months Ended
	Dec. 31, 2024
Equity [Abstract]
Equity	Equity The Company depends on earnings and dividends from its subsidiaries to pay dividends on common stock. The Company has paid quarterly dividends for 87 consecutive years. For the years ended December 31, 2024, 2023 and 2022, dividends declared on common stock were $.5100, $.6950 and $.8750 per common share, respectively. Dividends on common stock are paid quarterly to the stockholders as of the record date. For the years ended December 31, 2024, 2023 and 2022, the dividends declared to common stockholders were $103.9 million, $141.5 million and $177.9 million, respectively. The declaration and payment of dividends of the Company is at the sole discretion of the board of directors. In addition, the Company's subsidiaries are generally restricted to paying dividends out of capital accounts or net assets. The following discusses the most restrictive limitations. Certain credit agreements and regulatory limitations of the Company's subsidiaries also contain restrictions on dividend payments. The most restrictive limitation requires the Company's subsidiaries not to permit the ratio of funded debt to capitalization to be greater than 65 percent. Based on this limitation, approximately $1.3 billion of the net assets of the Company's subsidiaries, which represents common stockholders' equity including retained earnings, would be restricted from use for dividend payments at December 31, 2024. The Company may sell any combination of common stock and debt securities if warranted by market conditions and the Company's capital requirements. Any public offer and sale of such securities will be made only by means of a prospectus meeting the requirements of the Securities Act and the rules and regulations thereunder. The K-Plan provides participants the option to invest in the Company's common stock. For the years ended December 31, 2024, 2023 and 2022, the K-Plan purchased shares of common stock on the open market. At December 31, 2024, there were 7.2 million shares of common stock reserved for original issuance under the K-Plan.

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2024
Share-Based Payment Arrangement [Abstract]
Stock-Based Compensation	Stock-Based Compensation The Company has stock-based compensation plans under which it is currently authorized to grant RSUs and other stock awards. As of December 31, 2024, there were 2.3 million remaining shares available to grant under these plans. The Company either purchases shares on the open market or issues new shares of common stock to satisfy the vesting of stock-based awards. Separations of Knife River and Everus In connection with the completed separations of Knife River and Everus through spinoffs, the provisions of the existing compensation plans required adjustments to the number and terms of outstanding employee time-vested RSUs and PSAs to preserve the intrinsic value of the awards immediately prior to each separation. The outstanding awards will continue to vest over the original vesting period, which is generally three years from the grant date. The outstanding PSAs in place at the time of the Knife River spinoff were modified to no longer be subject to performance-based vesting conditions. The number of PSAs were first adjusted for performance. The combined performance factors were determined based on the performance of the Company as of December 31, 2022. As a result, there were no outstanding PSAs at December 31, 2023. Outstanding awards at the time of the spinoffs were converted into awards of the holder’s employer following each separation. The Company incurred $1.7 million of incremental compensation expense related to the conversion of the RSUs associated with the Everus spinoff, of which $854,000 was recognized in 2024 and the remainder will be recognized in expense over the remaining service periods of the applicable awards. Total stock-based compensation expense (after tax) was $7.1 million, $5.1 million and $6.9 million in 2024, 2023 and 2022, respectively. The Company uses the straight-line amortization method to recognize compensation expense related to RSUs, which only has a service condition. The Company recognized compensation expense related to PSAs with market-based performance metrics on a straight-line basis over the requisite service period. As of December 31, 2024, total remaining unrecognized compensation expense related to stock-based compensation was approximately $8.4 million (before income taxes) which will be amortized over a weighted average period of 1.3 years. Stock awards Non-employee directors receive shares of common stock in addition to and in lieu of cash payment for directors' fees. There were 46,341 shares with a fair value of $850,000, 50,717 shares with a fair value of $950,000 and 40,800 shares with a fair value of $1.2 million issued to non-employee directors during the years ended December 31, 2024, 2023 and 2022, respectively. RSUs In February 2024, 2023 and 2022, key employees were granted RSUs under the long-term performance-based incentive plan authorized by the Company's compensation committee. The compensation committee has the authority to select the recipients of awards, determine the type and size of awards, and establish certain terms and conditions of unit award grants. The shares vest over three years, contingent on continued employment. Compensation expense is recognized over the vesting period. Upon vesting, participants receive dividends that accumulate during the vesting period. As previously discussed, adjustments were made to the number of RSUs to preserve the intrinsic value of the awards in connection with the spinoffs of Knife River and Everus and outstanding PSAs in place at the time of the Knife River spinoff were converted to RSUs. Target grants of RSUs outstanding at December 31, 2024, were as follows: Grant Date Performance Period Target Grant of Shares February 2023/ July 2023 2023-2025 542,233 February 2024/ June 2024 2024-2026 698,284 A summary of the status of the RSUs for the year ended December 31, 2024, was as follows: RSUs Number of Shares Weighted ** Nonvested at beginning of period 873,300 $ 21.16 Granted pre-separation of Everus 478,938 20.89 Forfeited (112,826) 21.35 Non-vested pre-separation of Everus 1,239,412 Adjustments related to the Everus separation* 663,661 Vested shares (662,556) 12.04 Nonvested at end of period 1,240,517 $ 12.56 * Includes the conversion adjustments to preserve the intrinsic value of the awards and the cancellation of outstanding awards held by employees that transferred to Everus, which were replaced with awards issued by Everus as part of the separation. ** Weighted average grant-date fair values post-separation of Everus reflects incremental fair value related to modifying the awards and the Company's adjusted stock price due to the separation. Historical PSAs In February 2022, key employees were granted PSAs under the long-term performance-based incentive plan authorized by the Company's compensation committee. The compensation committee has the authority to select the recipients of awards, determine the type and size of awards, and establish certain terms and conditions of award grants. Upon vesting, participants receive dividends that accumulate during the vesting period. Share awards were generally earned over a three-year vesting period and tied to financial metrics. However, in connection with the spinoff of Knife River, the outstanding PSAs were converted to RSUs. As a result, there were no outstanding PSAs at December 31, 2024. Under the market condition for these PSAs, participants could earn from zero to 200 percent of the apportioned target grant of shares based on the Company's total stockholder return relative to that of the selected peer group. Compensation expense was based on the grant-date fair value as determined by Monte Carlo simulation. The blended volatility term structure ranges were comprised of 50 percent historical volatility and 50 percent implied volatility. Risk-free interest rates were based on U.S. Treasury security rates in effect as of the grant date. Assumptions used for initial grants applicable to the market condition for certain PSAs issued in 2022 were: 2022 Weighted average grant-date fair value $36.25 Blended volatility range 24.07% - 31.41% Risk-free interest rate range .71% - 1.68% Weighted average discounted dividends per share $2.93 Under the performance conditions for these PSAs, participants could earn from zero to 200 percent of the apportioned target grant of shares. The performance conditions were based on the Company's compound annual growth rate in earnings from continuing operations. The weighted average grant-date fair value per share for the PSAs applicable to these performance conditions issued in 2022 was $27.73. The fair value of the PSAs that vested during the year ended December 31, 2022, was $7.6 million.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Loss	12 Months Ended
	Dec. 31, 2024
Equity [Abstract]
Accumulated Other Comprehensive Loss	Accumulated Other Comprehensive Loss The Company's accumulated other comprehensive loss is comprised of losses on derivative instruments qualifying as hedges, postretirement liability adjustments and gain (loss) on available-for-sale investments. The after-tax changes in the components of accumulated other comprehensive loss were as follows: Net Post- Net Total (In thousands) At December 31, 2022 $ (125) $ (29,900) $ (558) $ (30,583) Other comprehensive income (loss) before reclassifications — (646) 173 (473) Amounts reclassified from accumulated other comprehensive loss 81 242 43 366 Net current-period other comprehensive income (loss) 81 (404) 216 (107) Amounts reclassified related to the separation of Knife River 44 12,262 — 12,306 At December 31, 2023 — (18,042) (342) (18,384) Other comprehensive income before reclassifications — 1,049 85 1,134 Amounts reclassified from accumulated other comprehensive loss — 432 20 452 Net current-period other comprehensive income — 1,481 105 1,586 At December 31, 2024 $ — $ (16,561) $ (237) $ (16,798) The following amounts were reclassified out of accumulated other comprehensive loss into net income. The amounts presented in parentheses indicate a decrease to net income on the Consolidated Statements of Income. The reclassifications for the years ended December 31 were as follows: 2024 2023 Location on Consolidated (In thousands) Reclassification adjustment for loss on derivative instruments included in net income $ — $ (96) Interest expense — 15 Income taxes — (81) Amortization of postretirement liability losses included in net periodic benefit credit (577) (320) Other income 145 78 Income taxes (432) (242) Reclassification adjustment on available-for-sale investments included in net income (25) (54) Other income 5 11 Income taxes (20) (43) Total reclassifications $ (452) $ (366)

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2024
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The components of income before income taxes from continuing operations for each of the years ended December 31 were as follows: 2024 2023 2022 (In thousands) United States $ 198,662 $ 340,330 $ 123,447 Income before income taxes from continuing operations $ 198,662 $ 340,330 $ 123,447 Income tax expense (benefit) from continuing operations for the years ended December 31 was as follows: 2024 2023 2022 (In thousands) Current: Federal $ 30,412 $ 8,271 $ (15,849) State 3,255 3,251 1,857 33,667 11,522 (13,992) Deferred: Income taxes: Federal (17,321) (3,331) 15,038 State (1,805) (125) 4,251 Investment tax credit - net 3,048 2,147 898 (16,078) (1,309) 20,187 Total income tax expense $ 17,589 $ 10,213 $ 6,195 Components of deferred tax assets and deferred tax liabilities at December 31 were as follows: 2024 2023 (In thousands) Deferred tax assets: Environmental compliance $ 33,730 $ 28,873 Pension and postretirement 25,508 27,584 Compensation-related 15,651 17,106 Customer advances 9,719 8,312 Cost recovery mechanisms 7,402 5,314 Legal and environmental contingencies 5,317 4,881 Other 20,386 13,045 Total deferred tax assets 117,713 105,115 Deferred tax liabilities: Basis differences on property, plant and equipment 426,493 404,039 Pension and postretirement 48,355 39,110 Purchased gas adjustment 20,441 34,618 Environmental compliance 17,260 16,221 Cost recovery mechanisms 19,245 22,604 Legal and environmental contingencies 6,300 5,902 Other 19,931 33,947 Total deferred tax liabilities 558,025 556,441 Valuation allowance 1,008 1,010 Net deferred income tax liability $ 441,320 $ 452,336 As of both December 31, 2024 and 2023, the Company had various state income tax net operating loss carryforwards of $1.0 million and state income tax credit carryforwards, excluding alternative minimum tax credit carryforwards, of $31.6 million and $33.7 million, respectively. The state income tax credit carryforwards are due to expire between 2026 and 2038. Changes in tax regulations or assumptions regarding current and future taxable income could require additional valuation allowances in the future. The following table reconciles the change in the net deferred income tax liability from December 31, 2023, to December 31, 2024, to deferred income tax expense: 2024 (In thousands) Change in net deferred income tax liability from the preceding table $ (11,016) Excess deferred income tax amortization (8,121) Deferred taxes associated with other comprehensive income (532) Other 3,591 Deferred income tax expense for the period $ (16,078) Total income tax expense differs from the amount computed by applying the statutory federal income tax rate to income before taxes. The reasons for this difference were as follows: Years ended December 31, 2024 2023 2022 Amount % Amount % Amount % (Dollars in thousands) Computed tax at federal statutory rate $ 41,719 21.0 $ 71,469 21.0 $ 25,924 21.0 Increases (reductions) resulting from: State income taxes, net of federal income tax 4,047 2.0 3,605 1.1 2,484 2.0 State investment tax credit, net of federal income tax 2,400 1.2 1,545 .5 1,624 1.3 Executive compensation 2,111 1.1 564 .2 683 .6 Federal renewable energy credit (16,871) (8.5) (15,175) (4.5) (15,343) (12.4) Excess deferred income tax amortization (8,121) (4.1) (8,383) (2.5) (9,008) (7.3) State tax rate change (2,317) (1.2) (9) — (3) — Research and development tax credit (1,465) (.7) (1,985) (.6) (1,692) (1.4) Nonqualified benefit plans (1,142) (.6) (1,313) (.4) 1,516 1.2 Tax-free debt for equity exchange — — (38,967) (11.4) — — Other (2,772) (1.4) (1,138) (.3) 10 — Total income tax expense $ 17,589 8.8 $ 10,213 3.1 $ 6,195 5.0 The Company's effective tax rate for 2024 differs from the U.S. federal statutory rate of 21 percent due primarily to the impact of credits and deductions provided by law and excess deferred income tax amortization. The Company and its subsidiaries file income tax returns in the U.S. federal jurisdiction, and various state and local jurisdictions. The Company is no longer subject to U.S. federal, non-U.S., state or local income tax examinations by tax authorities for years ending prior to 2020. Total reserves for uncertain tax positions were not material. The Company recognizes interest and penalties accrued relative to unrecognized tax benefits in income tax expense.

Cash Flow Information

Cash Flow Information	12 Months Ended
	Dec. 31, 2024
Supplemental Cash Flow Information [Abstract]
Cash Flow Information	Cash Flow Information Cash expenditures for interest and income taxes for the years ended December 31 were as follows: 2024 2023 2022 (In thousands) Interest, net* $ 108,242 $ 112,839 $ 49,036 Income taxes paid (refunded), net** $ 43,572 $ 12,162 $ (27,884) * AFUDC - borrowed was $11.0 million, $10.0 million and $2.2 million for the years ended December 31, 2024, 2023 and 2022, respectively. ** Income taxes paid, including discontinued operations, were $80.9 million, $62.5 million and $26.4 million for the years ended December 31, 2024, 2023 and 2022, respectively. Noncash investing and financing transactions at December 31 were as follows: 2024 2023 2022 (In thousands) Property, plant and equipment additions in accounts payable $ 36,820 $ 46,364 $ 34,886 Right-of-use assets obtained in exchange for new operating lease liabilities $ 1,787 $ 2,265 $ 1,324 Debt for equity exchange of retained shares in Knife River $ — $ 293,239 $ —

Business Segment Data

Business Segment Data	12 Months Ended
	Dec. 31, 2024
Segment Reporting [Abstract]
Business Segment Data	Business Segment Data The Company's reportable segments are those that are based on the Company's method of internal reporting, which generally segregates the strategic business activities due to differences in products, services and regulation. The internal reporting of these operating segments is defined based on the reporting and review process used by the Company's CODM, the chief executive officer. The Company's operations are located within the United States. The Company’s CODM regularly reviews discrete financial information of each reportable segment and uses net income to assess performance of each reportable segment. The CODM uses this information to assess performance and make decisions about resources to be allocated to each reportable segment, including capital and personnel. The information provided to the CODM is prepared at the reportable segment level in quarterly financial packages and on a more summarized basis monthly. Budget and forecast information is also provided to the CODM at the reportable segment level. The electric segment generates, transmits and distributes electricity in Montana, North Dakota, South Dakota and Wyoming. The natural gas distribution segment distributes natural gas in those states, as well as in Idaho, Minnesota, Oregon and Washington. These operations also supply related value-added services. The pipeline segment provides natural gas transportation and underground storage services through a FERC regulated pipeline system primarily in the Rocky Mountain and northern Great Plains regions of the United States. This segment also provides non-regulated energy-related services, including cathodic protection. The Other category includes the activities of Centennial Capital, which, through its subsidiary InterSource Insurance Company, insures various types of risks as a captive insurer for certain of the Company's subsidiaries. The function of the captive insurer is to fund the self-insured layers of the insured Company's general liability, automobile liability, pollution liability and other coverages. Centennial Capital also owns certain personal property. In addition, the Other category includes certain assets, liabilities and tax adjustments of the holding company primarily associated with corporate functions, as well as the gain on the tax-free exchange of the retained shares in Knife River and costs associated with certain strategic initiatives. Also included are certain general and administrative costs (reflected in operation and maintenance expense) and interest expense, which were previously allocated to Knife River, Everus, Fidelity and the refining business and did not meet the criteria for discontinued operations. Discontinued operations includes the results of operations for Knife River and Everus and certain associated separation costs, including interest on certain debt facilities repaid in connection with the separations. For the comparative periods below, Everus' operations are only reflected through October 2024 compared to the full year in 2023 and 2022 and Knife River's operations are only reflected through May 2023, compared to the full year in 2022. Discontinued operations also includes the supporting activities of Fidelity other than certain general and administrative costs and interest expense as described above. The information below follows the same accounting policies as described in Note 2. Information on the Company's segments as of December 31 and for the years then ended was as follows: Year ended December 31, 2024 Electric Natural gas distribution Pipeline Other Consolidated (In thousands) Operating revenues: External operating revenues $ 414,406 $ 1,200,975 $ 142,597 $ — $ 1,757,978 Intersegment operating revenues 72 130 69,222 195 69,619 Operation and maintenance: External operation and maintenance 94,897 231,087 75,456 13,051 414,491 Intersegment operation and maintenance 72 130 324 195 721 Purchased natural gas sold: External purchased natural gas sold — 630,403 — — 630,403 Intersegment purchased natural gas sold — 68,898 — — 68,898 Electric fuel and purchased power 141,148 — — — 141,148 Depreciation and amortization 66,524 101,958 29,362 2,234 200,078 Taxes, other than income 17,605 76,042 12,175 394 106,216 Other income: External other income 8,205 25,509 5,850 1,803 41,367 Intersegment other income — — 655 14,798 15,453 Interest expense: External interest expense 30,058 63,185 10,862 4,242 108,347 Intersegment interest expense — — 4,633 10,820 15,453 Income tax expense (benefit) (2,414) 7,974 17,470 (5,441) 17,589 Income (loss) from continuing operations 74,793 46,937 68,042 (8,699) 181,073 Discontinued operations, net of tax — — — 100,035 100,035 Net income $ 74,793 $ 46,937 $ 68,042 $ 91,336 $ 281,108 Capital expenditures (a) $ 110,812 $ 286,152 $ 126,806 $ 1,728 $ 525,498 Assets $ 1,976,912 (b) $ 3,730,532 (b) $ 1,151,317 $ 180,057 (c) $ 7,038,818 Property, plant and equipment $ 2,480,816 (b) $ 3,731,093 (b) $ 1,338,006 $ 4,148 $ 7,554,063 Accumulated depreciation and amortization $ 716,736 (b) $ 1,139,223 (b) $ 351,045 $ 2,767 $ 2,209,771 (a) Capital expenditures include noncash transactions such as capital expenditure-related accounts payable and AFUDC totaling $7.1 million. (b) Includes allocations of common utility property for the Electric and Natural gas distribution segments. (c) Other includes assets not directly assignable to a business (i.e. cash, cash equivalents and restricted cash, certain accounts receivable, certain investments and other miscellaneous current and deferred assets). Year ended December 31, 2023 Electric Natural gas distribution Pipeline Other Consolidated (In thousands) Operating revenues: External operating revenues $ 401,037 $ 1,287,236 $ 115,079 $ — $ 1,803,352 Intersegment operating revenues 138 301 62,533 119 63,091 Operation and maintenance: External operation and maintenance 92,521 219,481 70,386 24,693 407,081 Intersegment operation and maintenance 138 301 431 119 989 Purchased natural gas sold: External purchased natural gas sold — 742,965 — — 742,965 Intersegment purchased natural gas sold — 62,102 — — 62,102 Electric fuel and purchased power 134,779 — — — 134,779 Depreciation and amortization 64,253 95,300 26,811 4,086 190,450 Taxes, other than income 16,695 75,207 10,822 409 103,133 Realized gain on tax-free exchange of the retained shares in Knife River — — — 186,556 186,556 Other income: External other income 5,815 20,867 3,675 3,097 33,454 Intersegment other income — — 217 13,431 13,648 Interest expense: External interest expense 28,064 57,601 9,428 9,531 104,624 Intersegment interest expense — — 3,842 9,806 13,648 Income tax expense (benefit) (1,019) 6,927 12,409 (8,104) 10,213 Income from continuing operations 71,559 48,520 47,375 162,663 330,117 Discontinued operations, net of tax — — (457) 85,047 84,590 Net income $ 71,559 $ 48,520 $ 46,918 $ 247,710 $ 414,707 Capital expenditures (a) $ 109,805 $ 274,836 $ 115,903 $ (2,825) $ 497,719 Assets $ 1,955,644 (b) $ 3,532,142 (b) $ 1,045,704 $ 1,299,669 (c) $ 7,833,159 Property, plant and equipment $ 2,369,039 (b) $ 3,462,187 (b) $ 1,218,387 $ 31,654 $ 7,081,267 Accumulated depreciation and amortization $ 660,438 (b) $ 1,068,037 (b) $ 328,010 $ 19,890 $ 2,076,375 (a) Capital expenditures include noncash transactions such as capital expenditure-related accounts payable and AFUDC totaling $(13.6) million. (b) Includes allocations of common utility property for the Electric and Natural gas distribution segments. (c) Other includes assets of discontinued operations and assets not directly assignable to a business (i.e. cash, cash equivalents and restricted cash, certain accounts receivable, certain investments and other miscellaneous current and deferred assets). Year ended December 31, 2022 Electric Natural gas distribution Pipeline Other Consolidated (In thousands) Operating revenues: External operating revenues $ 377,015 $ 1,273,588 $ 96,695 $ — $ 1,747,298 Intersegment operating revenues 58 216 58,884 86 59,244 Operation and maintenance: External operation and maintenance 93,236 205,009 60,300 21,406 379,951 Intersegment operation and maintenance 58 216 638 86 998 Purchased natural gas sold: External purchased natural gas sold — 757,883 — — 757,883 Intersegment purchased natural gas sold — 58,246 — — 58,246 Electric fuel and purchased power 119,405 — — — 119,405 Depreciation and amortization 67,802 89,466 26,857 4,435 188,560 Taxes, other than income 16,917 71,095 12,318 299 100,629 Other income: External other income 528 3,213 1,272 (1,753) 3,260 Intersegment other income — — 80 556 636 Interest expense: External interest expense 28,526 42,126 9,966 65 80,683 Intersegment interest expense — — 136 500 636 Income tax expense (benefit) (5,420) 7,805 10,522 (6,712) 6,195 Income (loss) from continuing operations 57,077 45,171 36,194 (21,190) 117,252 Discontinued operations, net of tax — — (906) 251,143 250,237 Net income $ 57,077 $ 45,171 $ 35,288 $ 229,953 $ 367,489 Capital expenditures (a) $ 133,970 $ 240,064 $ 61,923 $ 2,272 $ 438,229 Assets $ 1,856,258 (b) $ 3,214,452 (b) $ 961,893 $ 3,628,178 (c) $ 9,660,781 Property, plant and equipment $ 2,276,613 (b) $ 3,208,059 (b) $ 1,108,141 $ 36,705 $ 6,629,518 Accumulated depreciation and amortization $ 625,813 (b) $ 1,009,788 (b) $ 308,516 $ 19,143 $ 1,963,260 (a) Capital expenditures include noncash transactions such as capital expenditure-related accounts payable and AFUDC totaling $4.4 million. (b) Includes allocations of common utility property for the Electric and Natural gas distribution segments. (c) Other includes assets of discontinued operations and assets not directly assignable to a business (i.e. cash, cash equivalents and restricted cash, certain accounts receivable, certain investments and other miscellaneous current and deferred assets). A reconciliation of reportable segment operating revenues and assets to consolidated operating revenues and assets is as follows: 2024 2023 2022 (In thousands) Operating revenues reconciliation: Total reportable segment operating revenues $ 1,827,402 $ 1,866,324 $ 1,806,456 Other revenue 195 119 86 Elimination of intersegment operating revenues (69,619) (63,091) (59,244) Total consolidated operating revenues $ 1,757,978 $ 1,803,352 $ 1,747,298 Asset reconciliation: Total reportable segment assets $ 6,892,959 $ 6,564,962 $ 6,061,151 Other assets 525,258 1,847,432 4,784,142 Elimination of intersegment receivables (379,399) (579,235) (1,184,512) Total consolidated assets $ 7,038,818 $ 7,833,159 $ 9,660,781

Employee Benefit Plans

Employee Benefit Plans	12 Months Ended
	Dec. 31, 2024
Retirement Benefits [Abstract]
Employee Benefit Plans	Employee Benefit Plans Pension and other postretirement benefit plans The Company has noncontributory qualified defined benefit pension plans and other postretirement benefit plans for certain eligible employees. The Company uses a measurement date of December 31 for all of its pension and postretirement benefit plans. Prior to 2013, defined benefit pension plan benefits and accruals for all nonunion and certain union plans were frozen and on June 30, 2015, the remaining union plan was frozen. These employees were eligible to receive additional defined contribution plan benefits. Effective January 1, 2010, eligibility to receive retiree medical benefits was modified at certain of the Company's businesses. Employees who had attained age 55 with 10 years of continuous service by December 31, 2010, were provided the option to choose between a pre-65 comprehensive medical plan coupled with a Medicare supplement or a specified company funded Retiree Reimbursement Account, regardless of when they retire. All other eligible employees must meet the new eligibility criteria of age 60 and 10 years of continuous service at the time they retire to be eligible for a specified company funded Retiree Reimbursement Account. Employees hired after December 31, 2009, will not be eligible for retiree medical benefits. In 2012, the Company modified health care coverage for certain retirees. Effective January 1, 2013, post-65 coverage was replaced by a fixed-dollar subsidy for retirees and spouses to be used to purchase individual insurance through a healthcare exchange. In connection with the previously discussed separation of Knife River on May 31, 2023, Knife River's pension plan, including the associated assets and liabilities, was transferred to Knife River and therefore is no longer reflected as part of the Company. Also in connection with the separation, a remeasurement of the Company's postretirement plan and the Company's unfunded, non-qualified defined benefit plan were performed and the applicable liabilities from the plans relating to transferring employees were transferred to Knife River. Changes in benefit obligation and plan assets and amounts recognized in the Consolidated Balance Sheets at December 31 were as follows: Pension Benefits Other 2024 2023 2024 2023 Change in benefit obligation: (In thousands) Benefit obligation at beginning of year $ 275,586 $ 278,286 $ 39,590 $ 40,315 Service cost — — 505 534 Interest cost 12,799 13,521 1,837 1,956 Plan participants' contributions — — 412 479 Actuarial (gain) loss (11,040) 5,395 (3,420) (215) Benefits paid (21,995) (21,616) (3,249) (3,479) Benefit obligation at end of year 255,350 275,586 35,675 39,590 Change in net plan assets: Fair value of plan assets at beginning of year 248,558 242,031 79,234 76,640 Actual return on plan assets 1,152 20,576 2,297 5,518 Employer contribution 2,911 7,567 71 76 Plan participants' contributions — — 412 479 Benefits paid (21,995) (21,616) (3,249) (3,479) Fair value of net plan assets at end of year 230,626 248,558 78,765 79,234 Funded status - (under) over $ (24,724) $ (27,028) $ 43,090 $ 39,644 Amounts recognized in the Consolidated Balance Sheets at December 31: Noncurrent assets - other $ — $ — $ 43,090 $ 39,644 Noncurrent liabilities - other 24,724 27,028 — — Benefit obligation (liabilities) assets - net amount recognized $ (24,724) $ (27,028) $ 43,090 $ 39,644 Amounts recognized in accumulated other comprehensive loss: Actuarial loss (gain) $ 13,228 $ 32,273 $ (809) $ (3,515) Prior service credit — — (37) (115) Total $ 13,228 $ 32,273 $ (846) $ (3,630) Amounts recognized in regulatory assets or liabilities: Actuarial loss (gain) $ 139,962 $ 140,232 $ (1,478) $ (1,146) Prior service credit — — (1,303) (2,619) Total $ 139,962 $ 140,232 $ (2,781) $ (3,765) Employer contributions and benefits paid in the preceding table include only those amounts contributed directly to, or paid directly from, plan assets. Amounts related to regulated operations are recorded as regulatory assets or liabilities and are expected to be reflected in rates charged to customers over time. For more information on regulatory assets and liabilities, see Note 6. In 2024, the actuarial gain recognized in the benefit obligation was primarily the result of an increase in the discount rate. In 2023, the actuarial loss recognized in the benefit obligation was primarily the result of a decrease in the discount rate. For more information on the discount rates, see the table below. Unrecognized pension actuarial gains and losses in excess of 10 percent of the greater of the projected benefit obligation or the market-related value of assets are amortized over the average life expectancy of plan participants for frozen plans. The market-related value of assets is determined using a five-year average of assets. The pension plans all have accumulated benefit obligations in excess of plan assets. The projected benefit obligation, accumulated benefit obligation and fair value of plan assets for these plans at December 31 were as follows: 2024 2023 (In thousands) Projected benefit obligation $ 255,350 $ 275,586 Accumulated benefit obligation $ 255,350 $ 275,586 Fair value of plan assets $ 230,626 $ 248,558 The components of net periodic benefit cost (credit), other than the service cost component, are included in other income on the Consolidated Statements of Income. Prior service credit is amortized on a straight-line basis over the average remaining service period of active participants. These components related to the Company's pension and other postretirement benefit plans for the years ended December 31 were as follows: Pension Benefits Other 2024 2023 2022 2024 2023 2022 Components of net periodic benefit cost (credit): (In thousands) Service cost $ — $ — $ — $ 505 $ 534 $ 894 Interest cost 12,799 13,521 9,396 1,837 1,956 1,383 Expected return on assets (16,113) (17,194) (17,482) (5,315) (5,361) (5,277) Amortization of prior service credit — — — (1,318) (1,318) (1,318) Recognized net actuarial loss (gain) 4,149 3,093 5,826 (288) (504) (570) Net periodic benefit cost (credit), including amount capitalized 835 (580) (2,260) (4,579) (4,693) (4,888) Less amount capitalized — — — — 107 175 Net periodic benefit cost (credit) 835 (580) (2,260) (4,579) (4,800) (5,063) Other changes in plan assets and benefit obligations recognized in accumulated comprehensive loss: Net loss (gain) 401 187 2,369 71 (604) (4,141) Amortization of actuarial (loss) gain (359) (292) (1,310) 130 108 (281) Amortization of prior service credit — — — 45 78 125 Reclassification of postretirement liability adjustment from regulatory asset — — 5,343 — — (992) Total recognized in accumulated other comprehensive loss 42 (105) 6,402 246 (418) (5,289) Other changes in plan assets and benefit obligations recognized in regulatory assets or liabilities: Net loss (gain) 3,520 1,826 9,757 (472) (107) 11,920 Amortization of actuarial (loss) gain (3,790) (2,801) (5,373) 158 304 500 Amortization of prior service credit — — — 1,273 1,273 1,273 Reclassification of postretirement liability adjustment from regulatory asset — — (5,343) — — 992 Total recognized in regulatory assets or liabilities (270) (975) (959) 959 1,470 14,685 Total recognized in net periodic benefit credit, accumulated other comprehensive loss and regulatory assets or liabilities $ 607 $ (1,660) $ 3,183 $ (3,374) $ (3,748) $ 4,333 Weighted average assumptions used to determine benefit obligations at December 31 were as follows: Pension Benefits Other 2024 2023 2024 2023 Discount rate 5.41 % 4.84 % 5.43 % 4.85 % Expected return on plan assets 6.50 % 6.50 % 6.00 % 6.00 % Weighted average assumptions used to determine net periodic benefit cost (credit) for the years ended December 31 were as follows: Pension Benefits Other 2024 2023 2024 2023 Discount rate 4.84 % 5.06 % 4.85 % 5.07 % Expected return on plan assets 6.50 % 6.50 % 6.00 % 6.00 % The expected rate of return on pension plan assets is based on a targeted asset allocation range determined by the funded ratio of the plan. As of December 31, 2024, the expected rate of return on pension plan assets is based on the targeted asset allocation range of 40 percent to 50 percent equity securities and 50 percent to 60 percent fixed-income securities and the expected rate of return from these asset categories. The expected rate of return on other postretirement plan assets is based on the targeted asset allocation range of 10 percent to 20 percent equity securities and 80 percent to 90 percent fixed-income securities and the expected rate of return from these asset categories. The expected return on plan assets for other postretirement benefits reflects insurance-related investment costs. Health care rate assumptions for the Company's other postretirement benefit plans as of December 31 were as follows: 2024 2023 Health care trend rate assumed for next year (pre-65/post-65) 8.5%/6.25% 7.5%/6.5% Health care cost trend rate - ultimate 4.5 % 4.5 % Year in which ultimate trend rate achieved (pre-65/post-65) 2035/2034 2034/2033 The Company's other postretirement benefit plans include health care and life insurance benefits for certain retirees. The plans underlying these benefits may require contributions by the retiree depending on such retiree's age and years of service at retirement or the date of retirement. The Company contributes a flat dollar amount to the monthly premiums which is updated annually on January 1. The Company expects to contribute to its defined benefit pension plans in 2025 the minimum funding requirement of $1.7 million. The Company expects to contribute approximately $18,000 to its postretirement benefit plans in 2025. The following benefit payments, which reflect future service, as appropriate, and expected Medicare Part D subsidies at December 31, 2024, are as follows: Years Pension Other Expected (In thousands) 2025 $ 22,280 $ 3,333 $ 48 2026 $ 22,070 $ 3,235 $ 43 2027 $ 21,870 $ 3,153 $ 37 2028 $ 21,500 $ 3,064 $ 32 2029 $ 21,170 $ 2,941 $ 27 2030-2034 $ 98,020 $ 13,659 $ 85 Outside investment managers manage the Company's pension and postretirement assets. The Company's investment policy with respect to pension and other postretirement assets is to make investments solely in the interest of the participants and beneficiaries of the plans and for the exclusive purpose of providing benefits accrued and defraying the reasonable expenses of administration. The Company strives to maintain investment diversification to assist in minimizing the risk of large losses. The Company's policy guidelines allow for investment of funds in cash equivalents, fixed-income securities and equity securities. The guidelines prohibit investment in commodities and futures contracts, equity private placement, employer securities, leveraged or derivative securities, options, direct real estate investments, precious metals, venture capital and limited partnerships. The guidelines also prohibit short selling and margin transactions. The Company's practice is to periodically review and rebalance asset categories based on its targeted asset allocation percentage policy. Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability (an exit price) in an orderly transaction between market participants at the measurement date. The fair value ASC establishes a hierarchy for grouping assets and liabilities, based on the significance of inputs. The estimated fair values of the Company's pension plans' assets are determined using the market approach. The carrying value of the pension plans' Level 2 cash equivalents approximates fair value and is determined using observable inputs in active markets or the net asset value of shares held at year end, which is determined using other observable inputs including pricing from outside sources. The estimated fair value of the pension plans' Level 1 and Level 2 equity securities are based on the closing price reported on the active market on which the individual securities are traded or other known sources including pricing from outside sources. The estimated fair value of the pension plans' Level 1 and Level 2 collective and mutual funds are based on the net asset value of shares held at year end, based on either published market quotations on active markets or other known sources including pricing from outside sources. The estimated fair value of the pension plans' Level 2 corporate and municipal bonds is determined using other observable inputs, including benchmark yields, reported trades, broker/dealer quotes, bids, offers, future cash flows and other reference data. The estimated fair value of the pension plans' Level 1 U.S. Government securities are valued based on quoted prices on an active market. The estimated fair value of the pension plans' Level 2 U.S. Government securities are valued mainly using other observable inputs, including benchmark yields, reported trades, broker/dealer quotes, bids, offers, to be announced prices, future cash flows and other reference data. The estimated fair value of the pension plans' Level 2 pooled separate accounts are determined using observable inputs in active markets or the net asset value of shares held at year end, or other observable inputs. Some of these securities are valued using pricing from outside sources. All investments measured at net asset value in the tables that follow are invested in commingled funds, separate accounts or common collective trusts which do not have publicly quoted prices. The fair value of the commingled funds, separate accounts and common collective trusts are determined based on the net asset value of the underlying investments. The fair value of the underlying investments held by the commingled funds, separate accounts and common collective trusts is generally based on quoted prices in active markets. Though the Company believes the methods used to estimate fair value are consistent with those used by other market participants, the use of other methods or assumptions could result in a different estimate of fair value. The fair value of the Company's pension plans' assets (excluding cash) by class were as follows: Fair Value Measurements at December 31, 2024, Using Quoted Prices Significant Significant Balance at December 31, 2024 (In thousands) Assets: Cash equivalents $ — $ 4,512 $ — $ 4,512 Equity securities: U.S. companies (2) — — (2) Collective and mutual funds (a) 72,777 93,606 — 166,383 U.S. Government securities 33,616 25,857 — 59,473 Investments measured at net asset value (b) — — — 260 Total assets measured at fair value $ 106,391 $ 123,975 $ — $ 230,626 (a) Collective and mutual funds invest approximately 39 percent in corporate bonds, 19 percent in U.S. Government securities, 17 percent in other investments, 15 percent in common stock of international companies, 9 percent in common stock of large-cap and mid-cap U.S. companies, and 1 percent cash and cash equivalents. (b) In accordance with ASC 820 - Fair Value Measurements, certain investments that were measured at net asset value per share (or its equivalent) have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the line items presented in the Consolidated Balance Sheets. Fair Value Measurements at December 31, 2023, Using Quoted Prices Significant Significant Balance at December 31, 2023 (In thousands) Assets: Cash equivalents $ — $ 7,197 $ — $ 7,197 Equity securities: U.S. companies (2) — — (2) Collective and mutual funds (a) 84,761 88,219 — 172,980 U.S. Government securities 30,162 33,141 — 63,303 Investments measured at net asset value (b) — — — 5,080 Total assets measured at fair value $ 114,921 $ 128,557 $ — $ 248,558 (a) Collective and mutual funds invest approximately 51 percent in corporate bonds, 15 percent in common stock of international companies, 11 percent in common stock of large-cap and mid-cap U.S. companies, 7 percent cash and cash equivalents, 7 percent in U.S. Government securities and 9 percent in other investments. (b) In accordance with ASC 820 - Fair Value Measurements, certain investments that were measured at net asset value per share (or its equivalent) have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the line items presented in the Consolidated Balance Sheets. The estimated fair values of the Company's other postretirement benefit plans' assets are determined using the market approach. The estimated fair value of the other postretirement benefit plans' Level 2 cash equivalents is valued at the net asset value of shares held at year end, based on published market quotations on active markets, or using other known sources including pricing from outside sources. The estimated fair value of the other postretirement benefit plans' Level 1 and Level 2 equity securities is based on the closing price reported on the active market on which the individual securities are traded or other known sources including pricing from outside sources. The estimated fair value of the other postretirement benefit plans' Level 2 insurance contract is based on contractual cash surrender values that are determined primarily by investments in managed separate accounts of the insurer. These amounts approximate fair value. The managed separate accounts are valued based on other observable inputs or corroborated market data. Though the Company believes the methods used to estimate fair value are consistent with those used by other market participants, the use of other methods or assumptions could result in a different estimate of fair value. The fair value of the Company's other postretirement benefit plans' assets (excluding cash) by asset class were as follows: Fair Value Measurements Quoted Prices Significant Significant Balance at December 31, 2024 (In thousands) Assets: Cash equivalents $ — $ 4,373 $ — $ 4,373 Equity securities: U.S. companies 2,880 — — 2,880 Insurance contract (a) — 71,512 — 71,512 Total assets measured at fair value $ 2,880 $ 75,885 $ — $ 78,765 (a) The insurance contract invests approximately 41 percent in corporate bonds, 28 percent in U.S. Government securities, 19 percent in common stock of large-cap U.S. companies, 6 percent in common stock of small-cap U.S. companies and 6 percent in other investments. Fair Value Measurements Quoted Prices Significant Significant Balance at December 31, 2023 (In thousands) Assets: Cash equivalents $ — $ 4,562 $ — $ 4,562 Equity securities: U.S. companies 2,369 — — 2,369 Insurance contract (a) — 72,303 — 72,303 Total assets measured at fair value $ 2,369 $ 76,865 $ — $ 79,234 (a) The insurance contract invests approximately 60 percent in corporate bonds, 16 percent in common stock of large-cap U.S. companies, 15 percent in U.S. Government securities, 5 percent in common stock of small-cap U.S. companies and 4 percent in other investments. Nonqualified benefit plans In addition to the qualified defined benefit pension plans reflected in the table at the beginning of this note, the Company also has unfunded, nonqualified defined benefit plans for executive officers and certain key management employees that generally provide for defined benefit payments at age 65 following the employee's retirement or, upon death, to their beneficiaries for a 15-year period. In February 2016, the Company froze the unfunded, nonqualified defined benefit plans to new participants and eliminated benefit increases. Vesting for participants not fully vested was retained. The projected benefit obligation and accumulated benefit obligation for these plans at December 31 were as follows: 2024 2023 (In thousands) Projected benefit obligation $ 52,007 $ 57,033 Accumulated benefit obligation $ 52,007 $ 57,033 The components of net periodic benefit cost are included in other income on the Consolidated Statements of Income. These components related to the Company's nonqualified defined benefit plans for the years ended December 31 were as follows: 2024 2023 2022 (In thousands) Components of net periodic benefit cost: Interest cost $ 2,568 $ 2,740 $ 1,681 Recognized net actuarial loss 365 273 911 Net periodic benefit cost $ 2,933 $ 3,013 $ 2,592 Weighted average assumptions used at December 31 were as follows: 2024 2023 Benefit obligation discount rate 5.26 % 4.73 % Benefit obligation rate of compensation increase N/A N/A Net periodic benefit cost discount rate 4.73 % 4.97 % Net periodic benefit cost rate of compensation increase N/A N/A The amount of future benefit payments for the unfunded, nonqualified defined benefit plans at December 31, 2024, are expected to aggregate as follows: 2025 2026 2027 2028 2029 2030-2034 (In thousands) Nonqualified benefits $ 5,700 $ 5,610 $ 5,830 $ 5,560 $ 5,190 $ 20,920 In 2012, the Company established a nonqualified defined contribution plan for certain key management employees. In 2020, the plan was frozen to new participants and no new Company contributions will be made to the plan after December 31, 2020. Vesting for participants not fully vested was retained. A new nonqualified defined contribution plan was adopted in 2020, effective January 1, 2021, to replace the plan originally established in 2012 with similar provisions. Expenses incurred under these plans for 2024, 2023 and 2022 were $4.0 million, $2.7 million and $538,000, respectively. The amount of investments that the Company anticipates using to satisfy obligations under these plans at December 31 was as follows: 2024 2023 (In thousands) Investments Insurance contracts* $ 59,282 $ 62,936 Life insurance** 30,834 31,303 Other 12,879 6,409 Total investments $ 102,995 $ 100,648 * For more information on the insurance contracts, see Note 9. ** Investments of life insurance are carried on plan participants (payable upon the employee's death). Defined contribution plans The Company sponsors a defined contribution plan for eligible employees and the costs incurred under this plan were $10.7 million in 2024, $17.0 million in 2023 and $14.3 million in 2022. Multiemployer plans The Company contributes to a MEPP under the terms of a collective-bargaining agreement that covers its union-represented employees. The risks of participating in this multiemployer plan is different from single-employer plans in the following aspects: • Assets contributed to the MEPP by one employer may be used to provide benefits to employees of other participating employers • If a participating employer stops contributing to the plan, the unfunded obligations of the plan may be borne by the remaining participating employers • If the Company chooses to stop participating in its MEPP, the Company may be required to pay those plans an amount based on the underfunded status of the plan, referred to as a withdrawal liability The Company's participation in this plan is outlined in the following table. Unless otherwise noted, the most recent Pension Protection Act zone status available in 2024 and 2023 is for the plan's year-end status at December 31, 2023, and December 31, 2022, respectively. The zone status is based on information that the Company received from the plan and is certified by the plan's actuary. Among other factors, a plan in the red zone is generally less than 65 percent funded, a plan in the yellow zone is between 65 percent and 80 percent funded, and a plan in the green zone is at least 80 percent funded. EIN/Pension Plan Number Pension Protection Act Zone Status FIP/RP Status Pending/Implemented Contributions Surcharge Imposed Expiration Date Pension Fund 2024 2023 2024 2023 2022 (In thousands) Idaho Plumbers and Pipefitters Pension Plan 826010346-001 Green as of 5/31/2024 Green as of 5/31/2023 No $ 1,434 $ 1,690 $ 1,613 No 3/31/2027 Total contributions $ 1,434 $ 1,690 $ 1,613 The Company was listed in the plans' Forms 5500 as providing more than 5 percent of the total contributions for the following plans and plan years: Pension Fund Year Contributions to Plan Exceeded More Than 5 Percent Idaho Plumbers and Pipefitters Pension Plan 2023 and 2022

Regulatory Matters

Regulatory Matters	12 Months Ended
	Dec. 31, 2024
Regulated Operations [Abstract]
Regulatory Matters	Regulatory Matters The Company regularly reviews the need for electric and natural gas rate changes in each of the jurisdictions in which service is provided. The Company files for rate adjustments to seek recovery of operating costs and capital investments, as well as reasonable returns as allowed by regulators. Certain regulatory proceedings and cases may also contain recurring mechanisms that can have an annual true-up. Examples of these recurring mechanisms include: infrastructure riders, transmission trackers, renewable resource cost adjustment riders, as well as weather normalization and decoupling mechanisms. The following paragraphs summarize the Company's significant open regulatory proceedings and cases by jurisdiction. The Company is unable to predict the ultimate outcome of these matters, the timing of final decisions of the various regulators and courts, or the effect on the Company's results of operations, financial position or cash flows. MTPSC On July 15, 2024, Montana-Dakota filed a request with the MTPSC for a natural gas general rate increase of approximately $9.4 million annually or 11.1 percent above current rates. The requested increase is primarily to recover investments in system upgrades and pipeline replacement projects enhancing the reliability, safety and integrity of the natural gas system, as well as increased costs to operate and maintain that system. On October 15, 2024, the MTPSC denied Montana-Dakota's request for an interim rate increase of approximately $8.0 million annually or 10.2 percent above current rates. On October 25, 2024, Montana-Dakota filed a motion for reconsideration of the interim rate increase. On January 14, 2025, the MTPSC approved an interim increase of approximately $7.7 million with interim rates effective on and after February 1, 2025. NDPSC On November 1, 2023, Montana-Dakota filed a request with the NDPSC for a natural gas general rate increase of approximately $11.6 million annually or 7.5 percent above current rates. The requested increase is primarily to recover investments in system upgrades and pipeline replacement projects enhancing the reliability, safety and integrity of the natural gas system, as well as increased costs to operate and maintain that system. On December 13, 2023, the NDPSC approved an interim rate increase of approximately $10.1 million annually or 6.5 percent above current rates, subject to refund, for service rendered on and after January 1, 2024. On September 16, 2024, an all-party settlement agreement was filed reflecting an annual revenue increase of $9.4 million or 6.1 percent overall. The reduction from the original filing includes lower incentives and a decreased return on equity. On November 7, 2024, the NDPSC approved the settlement with rates effective on and after December 1, 2024. Montana-Dakota has a renewable resource cost adjustment rate tariff that allows for annual adjustments for recent projected capital costs and related expenses for projects determined to be recoverable under the tariff. On November 1, 2024, Montana-Dakota filed an annual update to its renewable resource cost adjustment requesting to recover a revenue requirement of approximately $18.3 million annually. The update reflects a decrease of approximately $2.8 million annually from the revenues currently included in rates. The NDPSC approved the renewable resource cost adjustment on January 22, 2025, with rates effective February 1, 2025. WUTC On March 29, 2024, Cascade filed a request with the WUTC for a multi-year natural gas general rate increase of $43.8 million or 11.6 percent effective March 1, 2025 and $11.7 million or 2.8 percent to be effective March 1, 2026. Multi-year filings are now required by Washington law that went into effect on January 1, 2022. The requested increase is primarily to recover infrastructure investments necessary to provide safe and reliable service and higher operating costs due to inflation. On December 11, 2024, a multi-party settlement agreement was filed reflecting rate increases of $29.8 million or 7.9 percent proposed to be effective March 1, 2025, and $10.8 million or 2.6 percent proposed to be effective March 1, 2026. WYPSC On October 31, 2024, Montana-Dakota filed a request with the WYPSC for a natural gas general rate increase of approximately $2.6 million annually or 14.0 percent above current rates. The requested increase is primarily to recover investments in system upgrades and pipeline replacement projects enhancing the reliability, safety and integrity of the natural gas system, as well as increased costs to operate and maintain that system. This matter is pending before the WYPSC. FERC

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2024
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies The Company is party to claims and lawsuits arising out of its business and that of its consolidated subsidiaries, which may include, but are not limited to, matters involving property damage, personal injury, and environmental, contractual, statutory and regulatory obligations. The Company accrues a liability for those contingencies when the incurrence of a loss is probable and the amount can be reasonably estimated. If a range of amounts can be reasonably estimated and no amount within the range is a better estimate than any other amount, then the minimum of the range is accrued. The Company does not accrue liabilities when the likelihood that the liability has been incurred is probable but the amount cannot be reasonably estimated or when the liability is believed to be only reasonably possible or remote. For contingencies where an unfavorable outcome is probable or reasonably possible and which are material, the Company discloses the nature of the contingency and, in some circumstances, an estimate of the possible loss. Accruals are based on the best information available, but in certain situations management is unable to estimate an amount or range of a reasonably possible loss including, but not limited to when: (1) the damages are unsubstantiated or indeterminate, (2) the proceedings are in the early stages, (3) numerous parties are involved, or (4) the matter involves novel or unsettled legal theories. At December 31, 2024 and 2023, the Company accrued liabilities which have not been discounted of $24.1 million and $22.5 million, respectively. At December 31, 2024 and 2023, the Company also recorded corresponding insurance receivables of $24,000 and $152,000, respectively, and regulatory assets of $22.9 million and $21.6 million, respectively, related to the accrued liabilities. The accruals are for contingencies resulting from litigation and environmental matters. This includes amounts that have been accrued for matters discussed in Environmental matters within this note. The Company will continue to monitor each matter and adjust accruals as might be warranted based on new information and further developments. Management believes that the outcomes with respect to probable and reasonably possible losses in excess of the amounts accrued, net of insurance recoveries, while uncertain, either cannot be estimated or will not have a material effect upon the Company's financial position, results of operations or cash flows. Unless otherwise required by GAAP, legal costs are expensed as they are incurred. Environmental matters Manufactured Gas Plant Sites Claims have been made against Cascade for cleanup of environmental contamination at manufactured gas plant sites operated by Cascade's predecessors and a similar claim has been made against Montana-Dakota for a site operated by Montana-Dakota and its predecessors. Any accruals related to these claims are reflected in regulatory assets. For more information, see Note 6. Demand has been made of Montana-Dakota to participate in investigation and remediation of environmental contamination at a site in Missoula, Montana. The site operated as a former manufactured gas plant from approximately 1907 to 1938 when it was converted to a butane-air plant that operated until 1956. Montana-Dakota or its predecessors owned or controlled the site for a period of the time it operated as a manufactured gas plant and Montana-Dakota operated the butane-air plant from 1940 to 1951, at which time it sold the plant. There are no documented wastes or by-products resulting from the mixing or distribution of butane-air gas. Preliminary assessment of a portion of the site provided a recommended remedial alternative for that portion of approximately $560,000. However, the recommended remediation would not address any potential contamination to adjacent parcels that may be impacted from historic operations of the manufactured gas plant. An environmental assessment, which was started in 2020 and is still underway, is estimated to cost approximately $2.0 million. Montana-Dakota and another party agreed to voluntarily investigate and remediate the site and that Montana-Dakota will pay two-thirds of the costs for further investigation and remediation of the site. Montana-Dakota has accrued costs of $645,000 for the remediation and investigation costs and has incurred costs of $1.2 million as of December 31, 2024. Montana-Dakota received notice from a prior insurance carrier that it will participate in payment of defense costs incurred in relation to the claim. On December 9, 2021, Montana Dakota filed an application with the MTPSC for deferred accounting treatment for costs associated with the investigation and remediation of the site. The MTPSC approved the application for deferred accounting treatment as requested on July 26, 2022. A claim was made against Cascade for contamination at the Bremerton Gasworks Superfund Site in Bremerton, Washington, which was received in 1997. A preliminary investigation has found soil and groundwater at the site contain impacts requiring further investigation and cleanup. The EPA conducted a Targeted Brownfields Assessment of the site and released a report summarizing the results of that assessment in August 2009. The assessment confirmed that impacts have affected soil and groundwater at the site, as well as sediments in the adjacent Port Washington Narrows. In April 2010, the Washington DOE issued notice it considered Cascade a PRP for hazardous substances at the site. In May 2012, the EPA added the site to the National Priorities List of Superfund sites. Cascade entered into an administrative settlement agreement and consent order with the EPA regarding the scope and schedule for a remedial investigation and feasibility study for the site. Current estimates for the cost to complete the remedial investigation and feasibility study are approximately $16.0 million of which $11.7 million has been incurred as of December 31, 2024. Based on the site investigation, preliminary remediation alternative costs were provided by consultants in August 2020. The preliminary information received through the completion of the data report allowed for the projection of possible costs for a variety of site configurations, remedial measures and potential natural resource damage claims of between $13.6 million and $71.5 million. At December 31, 2024, Cascade has accrued $4.3 million for the remedial investigation and feasibility study, as well as $17.5 million for remediation of this site. The accrual for remediation costs will be reviewed and adjusted, if necessary, after the completion of the feasibility study. In April 2010, Cascade filed a petition with the WUTC for authority to defer the costs incurred in relation to the environmental remediation of this site. The WUTC approved the petition in September 2010, subject to conditions set forth in the order. A significant portion of the costs incurred to date have been recovered by insurance. A claim was made against Cascade for impacts at a site in Bellingham, Washington. Cascade received notice from a party in May 2008 that Cascade may be a PRP, along with other parties, for impacts from a manufactured gas plant owned by Cascade and its predecessor from about 1946 to 1962. Other PRPs reached an agreed order and work plan with the Washington DOE for completion of a remedial investigation and feasibility study for the site. A feasibility study prepared for one of the PRPs in March 2018 identifies five cleanup action alternatives for the site with estimated costs ranging from $8.0 million to $20.4 million with a selected preferred alternative having an estimated total cost of $9.3 million. The other PRPs developed a cleanup action plan and completed public review in 2020. The development of the remediation design is underway, with the Pre-Remedial Design Investigation Data Report and Engineering Design Report submitted to Washington Ecology in June 2023 and November 2024, respectively. The remedy construction is expected to commence in 2028 following the approval of the final design. Cascade believes its proportional share of any liability will be relatively small in comparison to other PRPs. The plant manufactured gas from coal between approximately 1890 and 1946. In 1946, shortly after Cascade's predecessor acquired the plant, the plant converted to a propane-air gas facility. There are no documented wastes or by-products resulting from the mixing or distribution of propane-air gas. Cascade has recorded an accrual for this site for an amount that is not material. The Company has received notices from and entered into agreements with certain of its insurance carriers that they will participate in the defense for certain contamination claims subject to full and complete reservations of rights and defenses to insurance coverage. To the extent these claims are not covered by insurance, the Company intends to seek recovery of remediation costs through its natural gas rates charged to customers. Purchase commitments The Company has entered into various commitments largely consisting of contracts for natural gas and coal supply; purchased power; natural gas transportation and storage; and information technology. Certain of these contracts are subject to variability in volume and price. The commitment terms vary in length, up to 35 years. The commitments under these contracts as of December 31, 2024, were: 2025 2026 2027 2028 2029 Thereafter (In thousands) Purchase commitments $ 658,012 $ 310,894 $ 210,152 $ 177,613 $ 147,081 $ 1,221,125 These commitments were not reflected in the Company's consolidated financial statements. Amounts purchased under various commitments for the years ended December 31, 2024, 2023 and 2022, were $841.7 million, $1.0 billion and $870.6 million, respectively. Guarantees The Company and certain subsidiaries have outstanding letters of credit to third parties related to insurance policies and other agreements, some of which are guaranteed by other subsidiaries of the Company. At December 31, 2024, the fixed maximum amounts guaranteed under these letters of credit aggregated $14.3 million. The amounts of scheduled expiration of the maximum amounts guaranteed under these letters of credit aggregate to $14.3 million in 2025. There were no amounts outstanding under the previously mentioned letters of credit at December 31, 2024. In the event of default under these letter of credit obligations, the Company or subsidiary guaranteeing the letter of credit would be obligated for reimbursement of payments made under the letter of credit. In the normal course of business, the Company and its subsidiaries have surety bonds. In the event the Company or its subsidiaries do not fulfill a bonded obligation, the Company or its subsidiaries would be responsible to the surety bond company for completion of the bonded contract or obligation. At December 31, 2024, approximately $15.6 million of surety bonds were outstanding, which were not reflected on the Consolidated Balance Sheet. Leases Most of the leases the Company enters into are for equipment, buildings, easements and vehicles as part of their ongoing operations. The Company also leases certain equipment to third parties through its utility business. The Company determines if an arrangement contains a lease at inception of a contract and accounts for all leases in accordance with ASC 842 - Leases. The recognition of leases requires the Company to make estimates and assumptions that affect the lease classification and the assets and liabilities recorded. The accuracy of lease assets and liabilities reported on the Consolidated Financial Statements depends on, among other things, management's estimates of interest rates used to discount the lease assets and liabilities to their present value, as well as the lease terms based on the unique facts and circumstances of each lease. Lessee accounting The leases the Company has entered into as part of its ongoing operations are considered operating leases and are recognized on the Consolidated Balance Sheets as noncurrent assets - other, current liabilities - other accrued liabilities noncurrent liabilities - other Generally, the leases for equipment have a term of five years or less and buildings and easements have a longer term of up to 35 years or more. To date, the Company does not have any residual value guarantee amounts probable of being owed to a lessor, financing leases or material agreements with related parties. The following tables provide information on the Company's operating leases at and for the years ended December 31: 2024 2023 2022 (In thousands) Lease costs: Short-term lease cost $ 1,549 $ 1,646 $ 1,373 Operating lease cost 3,069 2,871 2,497 Variable lease cost 819 676 413 $ 5,437 $ 5,193 $ 4,283 2024 2023 2022 (Dollars in thousands) Weighted average remaining lease term 12.65 years 15.35 years 15.15 years Weighted average discount rate 6.08 % 4.88 % 4.65 % Cash paid for amounts included in the measurement of lease liabilities $ 3,063 $ 2,868 $ 2,500 The reconciliation of future undiscounted cash flows to operating lease liabilities presented on the Consolidated Balance Sheet at December 31, 2024, was as follows: (In thousands) 2025 $ 3,034 2026 2,648 2027 2,011 2028 1,570 2029 1,492 Thereafter 20,808 Total 31,563 Less discount 10,654 Total operating lease liabilities $ 20,909 Lessor accounting The Company leases certain equipment to third parties through its utility businesses, which are considered short-term operating leases with terms of less than 12 months. Lease revenue was not material for the years ended December 31, 2024, 2023 and 2022, respectively. Variable interest entities The Company evaluates its arrangements and contracts with other entities to determine if they are VIEs and if so, if the Company is the primary beneficiary. Fuel Contract Coyote Station entered into a coal supply agreement with Coyote Creek that provides for the purchase of coal necessary to supply the coal requirements of the Coyote Station for the period May 2016 through December 2040. Coal purchased under the coal supply agreement is reflected in Inventories on the Consolidated Balance Sheets and is recovered from customers as a component of electric fuel and purchased power. The coal supply agreement creates a variable interest in Coyote Creek due to the transfer of all operating and economic risk to the Coyote Station owners, as the agreement is structured so that the price of the coal will cover all costs of operations, as well as future reclamation costs. The Coyote Station owners are also providing a guarantee of the value of the assets of Coyote Creek as they would be required to buy the assets at book value should they terminate the contract prior to the end of the contract term and are providing a guarantee of the value of the equity of Coyote Creek in that they are required to buy the entity at the end of the contract term at equity value. Although the Company has determined that Coyote Creek is a VIE, the Company has concluded that it is not the primary beneficiary of Coyote Creek because the authority to direct the activities of the entity is shared by the four unrelated owners of the Coyote Station, with no primary beneficiary existing. As a result, Coyote Creek is not required to be consolidated in the Company's financial statements. At December 31, 2024, the Company's exposure to loss as a result of the Company's involvement with the VIE, based on the Company's ownership percentage, was $25.6 million.

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2024
Subsequent Events [Abstract]
Subsequent Events	Subsequent EventsOn February 13, 2025, Montana-Dakota entered into a definitive purchase and sale agreement with Badger Wind, LLC, a subsidiary of Orsted Onshore North America, LLC. Pursuant to the terms of the agreement, Montana-Dakota will purchase a 49 percent undivided ownership interest in a wind project being constructed and located in North Dakota that is anticipated to have a net generating capacity of approximately 250 MW for a purchase price of $294.0 million, which would represent 122.5 MW of wind generation to be owned by Montana-Dakota. The purchase agreement is contingent on regulatory approval from the NDPSC. This transaction would reduce Montana-Dakota's purchase requirements under the existing power purchase agreement with Badger Wind, LLC, dated November 4, 2024.

Schedule I - Condensed Financia

Schedule I - Condensed Financial Information of Registrant	12 Months Ended
	Dec. 31, 2024
Condensed Financial Information Disclosure [Abstract]
Schedule I-Condensed Financial Information of Registrant	Condensed Financial Information of Registrant (Unconsolidated) Condensed Statements of Income and Comprehensive Income Years ended December 31, 2024 2023 2022 (In thousands) Operating revenues $ — $ — $ — Operating expenses 4,416 9,668 1,636 Operating loss (4,416) (9,668) (1,636) Realized gain on tax-free exchange of the retained shares in Knife River — 186,556 — Interest expense 642 7,109 — Income (loss) before income taxes (5,058) 169,779 (1,636) Income tax benefit (2,324) (4,220) (400) Equity in earnings of subsidiaries from continuing operations 183,807 156,118 118,488 Income from continuing operations 181,073 330,117 117,252 Equity in earnings of subsidiaries from discontinued operations 140,042 143,181 261,701 Discontinued operations, net of tax (40,007) (58,591) (11,464) Net income $ 281,108 $ 414,707 $ 367,489 Comprehensive income $ 282,694 $ 414,600 $ 377,910 The accompanying notes are an integral part of these condensed financial statements. Condensed Balance Sheets December 31, 2024 2023 (In thousands, except shares and per share amounts) Assets Current assets: Cash and cash equivalents $ 29,361 $ 33,039 Receivables, net 2,777 6,568 Accounts receivable from subsidiaries 31,955 30,526 Taxes receivable 5,799 — Prepayments and other current assets 3,210 8,261 Total current assets 73,102 78,394 Noncurrent assets Investments 37,264 37,722 Investment in subsidiaries 2,861,311 3,146,122 Notes receivable from subsidiaries — 58,000 Deferred income taxes 13,569 12,596 Operating lease right-of-use assets 160 31 Other 2,874 2,593 Total noncurrent assets 2,915,178 3,257,064 Total assets $ 2,988,280 $ 3,335,458 Liabilities and Stockholders' Equity Current liabilities: Accounts payable $ 4,076 $ 4,264 Accounts payable to subsidiaries 1,077 3,435 Notes payable to subsidiaries 198,035 134,107 Taxes payable — 542 Dividends payable 26,511 25,461 Accrued compensation 7,939 9,651 Operating lease liabilities due within one year 60 25 Other accrued liabilities 7,653 8,008 Total current liabilities 245,351 185,493 Noncurrent liabilities: Long-term debt, net of debt issuance costs (536) 57,048 Operating lease liabilities 100 6 Other 52,791 187,678 Total noncurrent liabilities 52,355 244,732 Commitments and contingencies Stockholders' equity: Common stock Authorized - 500,000,000 shares, $1.00 par value Shares issued - 203,934,578 at December 31, 2024 and 203,689,090 at December 31, 2023 203,935 203,689 Other paid-in capital 1,473,738 1,466,235 Retained earnings 1,029,699 1,253,693 Accumulated other comprehensive loss (16,798) (18,384) Total stockholders' equity 2,690,574 2,905,233 Total liabilities and stockholders' equity $ 2,988,280 $ 3,335,458 The accompanying notes are an integral part of these condensed financial statements. Condensed Statements of Cash Flows Years ended December 31, 2024 2023 2022 (In thousands) Net cash provided by operating activities of continuing operations $ 482,195 $ 282,132 $ 253,663 Net cash used in operating activities of discontinued operations (40,007) (58,591) (11,464) Net cash provided by operating activities 442,188 223,541 242,199 Investing activities: Investments in and advances to subsidiaries (211,000) (476,000) (45,000) Investments 2,253 7,422 (885) Repayment (issuance) of notes receivable 58,000 (58,000) — Net cash used in investing activities of continuing operations (150,747) (526,578) (45,885) Financing activities: Issuance of short-term borrowings — 535,000 — Repayment of short-term borrowings — (242,401) — Issuance of long-term debt — 443,000 — Repayment of long-term debt (58,000) (385,000) — Debt issuance costs (401) (952) — Proceeds from issuance of common stock (50) — (149) Dividends paid (102,939) (161,316) (176,915) Repurchase of common stock — (2,270) (3,525) Tax withholding on stock-based compensation (1,729) (1,471) (2,398) Net cash provided by (used in) financing activities of continuing operations (163,119) 184,590 (182,987) Net cash provided by (used in) financing activities of discontinued operations (132,000) 132,000 — Net cash provided by (used in) financing activities (295,119) 316,590 (182,987) Increase (decrease) in cash and cash equivalents (3,678) 13,553 13,327 Cash and cash equivalents - beginning of year 33,039 19,486 6,159 Cash and cash equivalents - end of year $ 29,361 $ 33,039 $ 19,486 The accompanying notes are an integral part of these condensed financial statements. Note 1 - Summary of Significant Accounting Policies Basis of presentation The condensed financial information reported in Schedule I is being presented to comply with Rule 12-04 of Regulation S-X. The information is unconsolidated and is presented for the parent company only, MDU Resources Group, Inc. (the Company) as of and for the years ended December 31, 2024, 2023 and 2022. In Schedule I, investments in subsidiaries are presented under the equity method of accounting where the assets and liabilities of the subsidiaries are not consolidated. The investments in net assets of the subsidiaries are recorded on the Condensed Balance Sheets. The income from subsidiaries is reported as equity in earnings of subsidiaries on the Condensed Statements of Income. The material cash inflows on the Condensed Statements of Cash Flows are primarily from the dividends and other payments received from its subsidiaries and the proceeds raised from the issuance of debt and equity securities. The consolidated financial statements of the Company reflect certain businesses as discontinued operations. These statements should be read in conjunction with the consolidated financial statements and notes thereto of the Company. Earnings per common share Please refer to the Consolidated Statements of Income of the registrant for earnings per common share. In addition, see Item 8 - Note 2 for information on the computation of earnings per common share. Note 2 - Debt MDU Resources Group, Inc. On May 31, 2023, the Company entered into a $150.0 million revolving credit agreement with a SOFR-based variable interest rate and a maturity date of May 29, 2024. At December 31, 2023, the Company had no amount outstanding, which remained that way until this agreement matured and subsequently terminated in May 2024. On May 31, 2023, the Company entered into a $200.0 million revolving credit agreement with a SOFR-based variable interest rate and a maturity date of May 31, 2028. Any borrowings under the revolving credit agreement are classified as long-term debt as they are intended to be refinanced on a long-term basis through continued borrowings. The credit agreement contains customary covenants and provisions, including a covenant of the Company not to permit, at any time, the ratio of total debt to total capitalization to be greater than 65 percent. The covenants also include certain restrictions on the sale of certain assets, loans and investments. At December 31, 2024, there were no amounts outstanding under the agreement. On May 31, 2023, the Company entered into a $375.0 million term loan agreement with a SOFR-based variable interest rate and a maturity date of May 31, 2025. On November 15, 2023, the Company paid down $185.0 million of the term loan agreement. On November 1, 2024, the Company repaid its remaining outstanding balance of $190.0 million and the term loan agreement subsequently terminated. The Company's repayment was funded by the Everus repayment of debt in connection with the separation. Refer to Note 3 for additional information related to the repayment of debt associated with the Everus separation. At December 31, 2024, the Company had no long-term debt maturities for 2025. For more information on debt, see Item 8 - Note 10. Note 3 - Dividends The Company depends on earnings and dividends from its subsidiaries to pay dividends on common stock. Cash dividends paid to the Company by subsidiaries were $418.3 million, $165.5 million and $242.1 million for the years ended December 31, 2024, 2023 and 2022, respectively.

Jointly Owned Facilities

Jointly Owned Facilities	12 Months Ended
	Dec. 31, 2024
Regulated Operations [Abstract]
Jointly Owned Facilities	Jointly Owned Facilities The consolidated financial statements include the Company's ownership interests in three coal-fired electric generating facilities (Big Stone Station, Coyote Station and Wygen III) and two major transmission lines (BSSE and JETx). Each owner of the jointly owned facilities is responsible for financing its investment. The Company's share of the jointly owned facilities operating expenses was reflected in the appropriate categories of operating expenses (electric fuel and purchased power; operation and maintenance; and taxes, other than income) in the Consolidated Statements of Income. At December 31, the Company's share of the cost of utility plant in service, construction work in progress and related accumulated depreciation for the jointly owned facilities was as follows: Ownership Percentage 2024 2023 (In thousands) Big Stone Station: 22.7 % Utility plant in service $ 155,302 $ 159,437 CWIP 318 197 Less accumulated depreciation 55,327 52,264 $ 100,293 $ 107,370 BSSE: 50.0 % Utility plant in service $ 111,043 $ 107,260 CWIP — — Less accumulated depreciation 10,359 8,111 $ 100,684 $ 99,149 Coyote Station: 25.0 % Utility plant in service $ 160,343 $ 160,208 CWIP 755 159 Less accumulated depreciation 115,133 113,187 $ 45,965 $ 47,180 JETx: 50.0 % Utility plant in service $ — $ — CWIP 6,112 1,372 Less accumulated depreciation — — $ 6,112 $ 1,372 Wygen III: 25.0 % Utility plant in service $ 67,851 $ 66,852 CWIP 97 127 Less accumulated depreciation 15,340 13,728 $ 52,608 $ 53,251

Pay vs Performance Disclosure

Pay vs Performance Disclosure - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Pay vs Performance Disclosure
Net income	$ 281,108	$ 414,707	$ 367,489

Insider Trading Arrangements

Insider Trading Arrangements	3 Months Ended
	Dec. 31, 2024
Trading Arrangements, by Individual
Rule 10b5-1 Arrangement Adopted	false
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false

Insider Trading Policies and Pr

Insider Trading Policies and Procedures	12 Months Ended
	Dec. 31, 2024
Insider Trading Policies and Procedures [Line Items]
Insider Trading Policies and Procedures Adopted	true

Cybersecurity Risk Management a

Cybersecurity Risk Management and Strategy Disclosure	12 Months Ended
	Dec. 31, 2024
Cybersecurity Risk Management, Strategy, and Governance [Line Items]
Cybersecurity Risk Management Processes for Assessing, Identifying, and Managing Threats [Text Block]	Overall Risk Management The Company has implemented a cyber risk management program to help ensure that the Company's electronic information and information systems are protected from various threats. The cyber risk management program is maintained as part of the Company's overall governance, ERM program and compliance program. The Company's information systems experience ongoing and often sophisticated cyberattacks by a variety of sources with the apparent aim to breach the Company's cyber-defenses. The Company has and may continue to face increased cyber risk due to the increased use of employee-owned devices and work from home arrangements. The Company is continuously reevaluating the need to upgrade and/or replace systems and network infrastructure. These upgrades and/or replacements could adversely impact operations by imposing substantial capital expenditures, creating delays or outages, or experiencing difficulties transitioning to new systems. System disruptions, if not anticipated and appropriately mitigated, could adversely affect the Company. The Company continually assesses risks from cybersecurity threats and adapts and enhances its controls accordingly. Risks from Cybersecurity Threats Any risks from previous cybersecurity threats, including as a result of any previous cybersecurity incidents, have not materially affected or are reasonably likely to materially affect the Company's business, financial condition, or results of operations. Such risks and incidents could have a material adverse effect in the future as cyberattacks continue to increase in frequency and sophistication. The Company also has cyber event related insurance. Employee Cybersecurity Training The Company provides ongoing cybersecurity training and compliance programs to facilitate education for employees who may have access to the Company's data and critical systems. Employee phishing tests are conducted on a monthly basis. Engage Third-parties on Risk Management Periodic external reviews, including penetration tests and security framework assessments, are conducted by auditors, external assessors, and/or consultants to assess and ensure compliance with the Company’s information security programs and practices. Internal and external auditors assess the Company’s information technology general controls on an annual basis. Oversee Third-party Risk The Company has implemented a third-party management risk program to help monitor and reduce risks associated with the Company's vendors, which includes processes such as completing due diligence on third party service providers before engaging with them for their services; assessing the third party’s cybersecurity posture by reviewing audit reports of the third party, completing cyber questionnaires, and reviewing applicable certification; including cybersecurity contractual language in contracts to limit risk; and monitoring and reassessing third party’s to ensure ongoing compliance with their cybersecurity obligations. Physical Security The Company safeguards assets through a standard physical security design process, including access controls, surveillance and monitoring, perimeter security controls, data center security, and incident response and reporting controls. Operational Technology The Company has operation technology, consisting of the hardware and software that monitors and controls devices, processes, and infrastructure related to the Company's operational assets. Security protocols for the Company's operational technology follow applicable NERC, FERC and TSA regulations and security directives. Other Risk Factors Notwithstanding the breadth of the Company's information security program, the Company may be unsuccessful in preventing or mitigating a cybersecurity event that could have a material adverse impact. See “Item 1A – Risk Factors – Other Risks – Technology disruptions or cyberattacks could adversely impact the Company's operations.”
Cybersecurity Risk Management Processes Integrated [Flag]	true
Cybersecurity Risk Management Processes Integrated [Text Block]	The Company has implemented a cyber risk management program to help ensure that the Company's electronic information and information systems are protected from various threats. The cyber risk management program is maintained as part of the Company's overall governance, ERM program and compliance program. The Company's information systems experience ongoing and often sophisticated cyberattacks by a variety of sources with the apparent aim to breach the Company's cyber-defenses. The Company has and may continue to face increased cyber risk due to the increased use of employee-owned devices and work from home arrangements. The Company is continuously reevaluating the need to upgrade and/or replace systems and network infrastructure. These upgrades and/or replacements could adversely impact operations by imposing substantial capital expenditures, creating delays or outages, or experiencing difficulties transitioning to new systems. System disruptions, if not anticipated and appropriately mitigated, could adversely affect the Company. The Company continually assesses risks from cybersecurity threats and adapts and enhances its controls accordingly.
Cybersecurity Risk Management Third Party Engaged [Flag]	true
Cybersecurity Risk Third Party Oversight and Identification Processes [Flag]	true
Cybersecurity Risk Materially Affected or Reasonably Likely to Materially Affect Registrant [Flag]	false
Cybersecurity Risk Board of Directors Oversight [Text Block]	Board of Directors Oversight The Company's board of directors, as a whole and through its committees, has responsibility for oversight of risk management. In its risk oversight role, the board of directors has the responsibility to satisfy itself that the risk management processes designed and implemented by management are adequate for identifying, assessing, and managing risk. The audit committee of the board of directors of the Company is responsible for oversight of risks from cybersecurity threats. Management's Role Managing Risk The Company's CIO plays a large role in informing the audit committee of the board of directors on cybersecurity risks. The audit committee of the board of directors receives presentations and reports from the CIO on cybersecurity related issues which include information security, technology risks and risk mitigation programs regularly at the quarterly board meetings. In addition to scheduled meetings, the CIO and audit committee of the board of directors maintain an ongoing dialogue regarding emerging or potential cybersecurity risks. Cybersecurity Incident Response The Company has an incident response plan to identify, protect, detect, respond to, and recover from cybersecurity threats and incidents that is also tested on an annual basis. The incident response plan is updated based on results of the test or as new cyber related developments occur. The CIO, executive leadership which includes the chief executive officer, chief financial officer, chief accounting officer, chief legal officer, and SEC financial reporting department employees, and the board of directors are notified of any material cybersecurity incidents through a defined escalation process. The defined escalation process is a risk-based process that specifies who is to be contacted and when at each risk level. Monitor, Manage, and Safeguard Against Cybersecurity Incidents and Risks The Company's CIO, along with its director of cybersecurity and a designated security team of professionals, are responsible for assessing and managing risks as well as developing and implementing policies, procedures, and practices based on the range of threats faced by the Company. There are processes around access management, data security, encryption, asset management, secure system development, security operations, network and device security to provide safeguards from a cybersecurity incident along with continual monitoring of various threat intelligence feeds. Cyber Risk Management Personnel The Company's director of cybersecurity reports to the CIO and the CIO reports directly to the Company's chief executive officer. The Company's CIO who served as the first CIO of the Company since 2016, oversaw the information technology and cybersecurity portfolios until her retirement on January 10, 2025. A new CIO from within the Company was named to succeed the retiring CIO and holds both a bachelor's and master's degree in business administration with over 25 years of information technology experience in the energy and utilities business. The director of cybersecurity has a bachelor’s degree in computer information systems, over 25 years of information security experience, and holds certified information systems security professional and certified risk and information systems control certifications. The other members of information technology director level leadership also responsible for managing cybersecurity risks have degrees including Bachelor of Computer Information Systems, information systems management, electronics, electrical engineering, business administration, and accounting, along with certified information systems auditor certification and a cybersecurity fundamentals certificate. Cyber Risk Oversight Committee
Cybersecurity Risk Board Committee or Subcommittee Responsible for Oversight [Text Block]	The Company's board of directors, as a whole and through its committees, has responsibility for oversight of risk management. In its risk oversight role, the board of directors has the responsibility to satisfy itself that the risk management processes designed and implemented by management are adequate for identifying, assessing, and managing risk. The audit committee of the board of directors of the Company is responsible for oversight of risks from cybersecurity threats.Additionally, in 2014 the board of directors established CyROC to provide executive management and the audit committee of the board of directors with analyses, appraisals, recommendations and pertinent information concerning cyber defense of the Company's electronic information, information technology and operation technology systems. The CyROC is responsible for guiding the Company's comprehensive cybersecurity policies and oversight of cybersecurity risks. The CyROC is chaired by the Company's CIO and is comprised of members such as the chief financial officer, information technology leaders, internal auditors, and other leaders from across the Company.
Cybersecurity Risk Process for Informing Board Committee or Subcommittee Responsible for Oversight [Text Block]	The Company's CIO plays a large role in informing the audit committee of the board of directors on cybersecurity risks. The audit committee of the board of directors receives presentations and reports from the CIO on cybersecurity related issues which include information security, technology risks and risk mitigation programs regularly at the quarterly board meetings. In addition to scheduled meetings, the CIO and audit committee of the board of directors maintain an ongoing dialogue regarding emerging or potential cybersecurity risks.
Cybersecurity Risk Role of Management [Text Block]	The Company's CIO plays a large role in informing the audit committee of the board of directors on cybersecurity risks. The audit committee of the board of directors receives presentations and reports from the CIO on cybersecurity related issues which include information security, technology risks and risk mitigation programs regularly at the quarterly board meetings. In addition to scheduled meetings, the CIO and audit committee of the board of directors maintain an ongoing dialogue regarding emerging or potential cybersecurity risks. Cybersecurity Incident Response The Company has an incident response plan to identify, protect, detect, respond to, and recover from cybersecurity threats and incidents that is also tested on an annual basis. The incident response plan is updated based on results of the test or as new cyber related developments occur. The CIO, executive leadership which includes the chief executive officer, chief financial officer, chief accounting officer, chief legal officer, and SEC financial reporting department employees, and the board of directors are notified of any material cybersecurity incidents through a defined escalation process. The defined escalation process is a risk-based process that specifies who is to be contacted and when at each risk level. Monitor, Manage, and Safeguard Against Cybersecurity Incidents and Risks The Company's CIO, along with its director of cybersecurity and a designated security team of professionals, are responsible for assessing and managing risks as well as developing and implementing policies, procedures, and practices based on the range of threats faced by the Company. There are processes around access management, data security, encryption, asset management, secure system development, security operations, network and device security to provide safeguards from a cybersecurity incident along with continual monitoring of various threat intelligence feeds. Cyber Risk Management Personnel The Company's director of cybersecurity reports to the CIO and the CIO reports directly to the Company's chief executive officer. The Company's CIO who served as the first CIO of the Company since 2016, oversaw the information technology and cybersecurity portfolios until her retirement on January 10, 2025. A new CIO from within the Company was named to succeed the retiring CIO and holds both a bachelor's and master's degree in business administration with over 25 years of information technology experience in the energy and utilities business. The director of cybersecurity has a bachelor’s degree in computer information systems, over 25 years of information security experience, and holds certified information systems security professional and certified risk and information systems control certifications. The other members of information technology director level leadership also responsible for managing cybersecurity risks have degrees including Bachelor of Computer Information Systems, information systems management, electronics, electrical engineering, business administration, and accounting, along with certified information systems auditor certification and a cybersecurity fundamentals certificate. Cyber Risk Oversight Committee
Cybersecurity Risk Management Positions or Committees Responsible [Flag]	true
Cybersecurity Risk Management Positions or Committees Responsible [Text Block]	The Company's CIO plays a large role in informing the audit committee of the board of directors on cybersecurity risks. The audit committee of the board of directors receives presentations and reports from the CIO on cybersecurity related issues which include information security, technology risks and risk mitigation programs regularly at the quarterly board meetings.
Cybersecurity Risk Management Expertise of Management Responsible [Text Block]	The Company's director of cybersecurity reports to the CIO and the CIO reports directly to the Company's chief executive officer. The Company's CIO who served as the first CIO of the Company since 2016, oversaw the information technology and cybersecurity portfolios until her retirement on January 10, 2025. A new CIO from within the Company was named to succeed the retiring CIO and holds both a bachelor's and master's degree in business administration with over 25 years of information technology experience in the energy and utilities business. The director of cybersecurity has a bachelor’s degree in computer information systems, over 25 years of information security experience, and holds certified information systems security professional and certified risk and information systems control certifications. The other members of information technology director level leadership also responsible for managing cybersecurity risks have degrees including Bachelor of Computer Information Systems, information systems management, electronics, electrical engineering, business administration, and accounting, along with certified information systems auditor certification and a cybersecurity fundamentals certificate.
Cybersecurity Risk Process for Informing Management or Committees Responsible [Text Block]	The Company has an incident response plan to identify, protect, detect, respond to, and recover from cybersecurity threats and incidents that is also tested on an annual basis. The incident response plan is updated based on results of the test or as new cyber related developments occur. The CIO, executive leadership which includes the chief executive officer, chief financial officer, chief accounting officer, chief legal officer, and SEC financial reporting department employees, and the board of directors are notified of any material cybersecurity incidents through a defined escalation process. The defined escalation process is a risk-based process that specifies who is to be contacted and when at each risk level.
Cybersecurity Risk Management Positions or Committees Responsible Report to Board [Flag]	true

Significant Accounting Polici_2

Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2024
Accounting Policies [Abstract]
Basis of presentation	The consolidated financial statements of the Company include the accounts of the following businesses: electric, natural gas distribution, pipeline and other. For further descriptions of the Company's businesses, see Note 17. On May 31, 2023, the Company completed the separation of Knife River, formerly the construction materials and contracting segment, resulting in Knife River becoming an independent, publicly-traded company. The Company's board of directors approved the distribution of approximately 90 percent of the issued and outstanding shares of Knife River to the Company's stockholders. Stockholders of the Company received one share of Knife River common stock for every four shares of the Company's common stock held on May 22, 2023, the record date for the distribution. The Company retained approximately 10 percent or 5.7 million shares of Knife River common stock immediately following the separation, which were disposed of in a tax-free exchange in November 2023. The separation of Knife River was a tax-free spinoff transaction to the Company's stockholders for U.S. federal income tax purposes, except for cash received in lieu of fractional shares. On October 31, 2024, the Company completed the separation of Everus, its construction services business, resulting in Everus becoming an independent, publicly-traded company. The Company's board of directors approved the distribution of all the outstanding shares of Everus common stock to the Company's stockholders. Stockholders of the Company received one share of Everus common stock for every four shares of the Company's common stock held as of the close of business on October 21, 2024, the record date for the distribution. The separation of Everus was a tax-free spinoff transaction to the Company's stockholders for U.S. federal income tax purposes, except for cash received in lieu of fractional shares. The Company's consolidated financial statements and accompanying notes for the current and prior periods have been restated to present the results of operations and the assets and liabilities of Knife River and Everus as discontinued operations, other than certain corporate overhead costs of the Company historically allocated to Knife River and Everus, which are reflected in Other. Also included in discontinued operations in the Consolidated Statements of Income are the supporting activities of Fidelity and certain interest expense related to financing activity associated with the Knife River and Everus separations. The assets and liabilities of the Company's discontinued operations are included in current assets of discontinued operations, noncurrent assets of discontinued operations, current liabilities of discontinued operations and noncurrent liabilities of discontinued operations on the Consolidated Balance Sheets. Unless otherwise indicated, the amounts presented in the accompanying notes to the consolidated financial statements relate to the Company's continuing operations. For more information on discontinued operations, see Note 3. Additionally, certain amounts recorded in prior year financial statements have been reclassified to conform to the current year presentation. The Company has reclassified $26.9 million and $27.4 million of transmission-related expenses from operation and maintenance to electric fuel and purchased power for the years ended December 31, 2023 and 2022, respectively, in the Consolidated Statements of Income. These transmission-related expenses are an integral component of the cost of electricity sold to customers and therefore, more appropriately reflected in electric fuel and purchased power than operation and maintenance expense. These reclassifications had no effect on previously reported results of operations or cash flows. Management has also evaluated the impact of events occurring after December 31, 2024, up to the date of issuance of these consolidated financial statements on February 20, 2025, that would require recognition or disclosure in the financial statements.
Principles of consolidation	Principles of consolidation The consolidated financial statements were prepared in accordance with GAAP and include the accounts of the Company and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation, except for certain transactions related to regulated operations in accordance with GAAP. For more information on intercompany revenues, see Note 17.
Use of estimates	Use of estimates
New accounting standards	New accounting standards The following table provides a brief description of the accounting pronouncements applicable to the Company and the potential impact on its financial statements and/or disclosures: Standard Description Effective date Impact on financial statements/disclosures Recently adopted accounting standards ASU 2022-06 - Reference Rate Reform: Deferral of Sunset Date In December 2022, the FASB included a sunset provision within ASC 848 based on expectations of when LIBOR would cease being published. At the time ASU 2020-04 was issued, the UK Financial Conduct Authority had established its intent to cease overnight tenors of LIBOR after December 31, 2021. In March 2021, the UK Financial Conduct Authority announced that the intended cessation date of the overnight tenors of LIBOR would be June 30, 2023 which is beyond the current sunset date of ASC 848. The amendments in this Update defer the sunset date of ASC 848 from December 31, 2022 to December 31, 2024, after which entities will no longer be permitted to apply the relief in ASC 848. December 31, 2024 The Company has updated its credit agreements to include language regarding the successor or alternate rate to LIBOR. The Company did not have a material impact on its results of operations, financial position, cash flows or disclosures. ASU 2023-07 Segment Reporting - Improvements to Reportable Segment Disclosures In November 2023, the FASB issued guidance on improving financial reporting by requiring disclosure of incremental segment information, primarily through enhanced disclosures about significant segment expenses, on an annual and interim basis for all public entities to enable investors to develop more decision-useful financial analyses. December 31, 2024 The Company identified and updated disclosures to ensure compliance with the new guidance. See Note 17. Recently issued accounting standards not yet adopted ASU 2023-09 Income Taxes - Improvements to Income Tax Disclosures an Amendment, December 2023 In December 2023, the FASB issued guidance to address investors requests for more transparency about income tax information through improvements to income tax disclosures primarily related to the rate reconciliation and income taxes paid information and effectiveness of income tax disclosures. Effective for annual reporting periods beginning after 2024 on a prospective basis. The Company is currently evaluating the impact the guidance will have on its disclosures for the year ended December 31, 2025. ASU 2024-01 Compensation - Stock Compensation In March 2024, the FASB issued Improvements to GAAP through an example to demonstrate application of the scope of paragraph 718-10-15-3 to determine whether profits interest and similar awards should be accounted in Compensation - Stock Compensation. Effective for fiscal year beginning after December 15, 2024. The Company is currently evaluating the impact the guidance will have on its disclosures for the year ended December 31, 2025. ASU 2024-03 Disaggregation of Income Statement Expenses In November 2024, the FASB issued guidance to improve the disclosures about a public business entity's expenses and address requests from investors for more detailed information about the types of expenses (including purchases of inventory, employee compensation, depreciation, amortization, and depletion) in commonly presented expense captions (such as cost of sales, selling, general, and administrative; and research and development). Effective for annual reporting periods beginning after December 15, 2026, and interim reporting periods beginning after December 15, 2027. The Company is currently evaluating the impact the guidance will have on its disclosures for the year ended December 31, 2027.
Cash, cash equivalents and restricted cash	Cash, cash equivalents and restricted cash
Revenue recognition	Revenue recognition Revenue is recognized when a performance obligation is satisfied by transferring control over a product or service to a customer. Revenue is measured based on consideration specified in a contract with a customer and excludes any sales incentives and amounts collected on behalf of third parties. The Company is considered an agent for certain taxes collected from customers. As such, the Company presents revenues net of these taxes at the time of sale to be remitted to governmental authorities, including sales and use taxes. The electric and natural gas distribution segments generate revenue from the sales of electric and natural gas products and services, which includes retail and transportation services. These segments establish a customer's retail or transportation service account based on the customer's application/contract for service, which indicates approval of a contract for service. The contract identifies an obligation to provide service in exchange for delivering or standing ready to deliver the identified commodity; and the customer is obligated to pay for the service as provided in the applicable tariff. The product sales are based on a fixed rate that includes a base and per-unit rate, which are included in approved tariffs as determined by state or federal regulatory agencies. The quantity of the commodity consumed or transported determines the total per-unit revenue. The service provided, along with the product consumed or transported, are a single performance obligation because both are required in combination to successfully transfer the contracted product or service to the customer. Revenues are recognized over time as customers receive and consume the products and services. The method of measuring progress toward the completion of the single performance obligation is on a per-unit output method basis, with revenue recognized based on the direct measurement of the value to the customer of the goods or services transferred to date. For contracts governed by the Company’s utility tariffs, amounts are billed monthly with the amount due between 15 and 22 days of receipt of the invoice depending on the applicable state’s tariff. For other contracts not governed by tariff, payment terms are net 30 days. At this time, the segment has no material obligations for returns, refunds or other similar obligations. The pipeline segment generates revenue from providing natural gas transportation and underground storage services, as well as other energy-related services to both third parties and internal customers, largely the natural gas distribution segment. The pipeline segment establishes a contract with a customer based upon the customer’s request for firm or interruptible natural gas transportation or storage service(s). The contract identifies an obligation for the segment to provide the requested service(s) in exchange for consideration from the customer over a specified term. Depending on the type of service(s) requested and contracted, the service provided may include transporting or storing an identified quantity of natural gas and/or standing ready to deliver or store an identified quantity of natural gas. Natural gas transportation and storage revenues are based on fixed rates, which may include reservation fees and/or per-unit commodity rates. The services provided by the segment are generally treated as single performance obligations satisfied over time simultaneous to when the service is provided and revenue is recognized. Rates for the segment’s regulated services are based on its FERC approved tariff or customer negotiated rates, and rates for its non-regulated services are negotiated with its customers and set forth in the contract. For contracts governed by the company’s tariff, amounts are billed on or before the ninth business day of the following month and the amount is due within 12 days of receipt of the invoice. For other contracts not governed by the tariff, payment terms are net 30 days. At this time, the segment has no material obligations for returns, refunds or other similar obligations. The Company recognizes all other revenues when services are rendered or goods are delivered.
Legal costs	Legal costs The Company generally expenses external legal fees as they are incurred unless it has specific circumstances to defer, such as probable recovery in a rate proceeding.
Receivables and allowance for expected credit losses	Receivables consist primarily of trade receivables from the sale of goods and services net of expected credit losses. The Company's trade receivables are all due in 12 months or less.The Company's expected credit losses are determined through a review using historical credit loss experience, changes in asset specific characteristics, current conditions and reasonable and supportable future forecasts, among other specific account data, and is performed at least quarterly. The Company develops and documents its methodology to determine its allowance for expected credit losses at each of its reportable business segments. Risk characteristics used by the business segments may include customer mix, knowledge of customers and general economic conditions of the various local economies, among others. Specific account balances are written off when management determines the amounts to be uncollectible. Management has reviewed the balance reserved through the allowance for expected credit losses and believes it is reasonable.
Inventories and natural gas in storage	Inventories and natural gas in storage
Property, plant and equipment	Property, plant and equipment Additions to property, plant and equipment are recorded at cost. When regulated assets are retired, or otherwise disposed of in the ordinary course of business, the original cost of the asset is charged to accumulated depreciation. With respect to the retirement or disposal of all other assets, the resulting gains or losses are recognized as a component of income.
Impairment of long-lived assets, excluding goodwill	Impairment of long-lived assets, excluding goodwill
Regulatory assets and liabilities	Regulatory assets and liabilities The Company is subject to various state and federal agency regulations. The accounting policies followed by the Company are generally subject to the Uniform System of Accounts of the FERC as well as the provisions of ASC 980 - Regulated Operations . These accounting policies differ in some respects from those used by the Company's non-regulated businesses. The Company accounts for certain income and expense items under the provisions of regulatory accounting, which requires the Company to defer as regulatory assets or liabilities certain items that would have otherwise been reflected as expense or income, respectively. The Company records regulatory assets or liabilities at the time the Company determines the amounts to be recoverable in current or future rates. Regulatory assets and liabilities are being amortized consistently with the regulatory treatment established by the FERC and the applicable state public service commission. See Note 6 for more information regarding the nature and amounts of these regulatory deferrals.
Goodwill	Goodwill Goodwill represents the excess of the purchase price over the fair value of identifiable net tangible and intangible assets acquired in a business combination. Goodwill is required to be tested for impairment annually, which the Company completes in the fourth quarter, or more frequently if events or changes in circumstances indicate that goodwill may be impaired. The Company has determined that the reporting units for its goodwill impairment test are its operating segments, or components of an operating segment, that constitute a business for which discrete financial information is available and for which segment management regularly reviews the operating results. As of December 31, 2024, the only operating segment with goodwill was the natural gas distribution segment. For more information on the Company's operating segments, see Note 17.
Investments	Investments The Company's investments include the cash surrender value of life insurance policies, insurance contracts, mortgage-backed securities and U.S. Treasury securities. The Company measures its investment in the insurance contracts at fair value with any unrealized gains and losses recorded on the Consolidated Statements of Income. The Company has not elected the fair value option for its mortgage-backed securities and U.S. Treasury securities and, as a result, the unrealized gains and losses on these investments are recorded in accumulated other comprehensive loss. For more information, see Notes 9 and 18.
Variable interest entities	Variable interest entities The Company evaluates its arrangements and contracts with other entities to determine if they are VIEs and if so, if the Company is the primary beneficiary. GAAP provides a framework for identifying VIEs and determining when a company should include the assets, liabilities, noncontrolling interest and results of activities of a VIE in its consolidated financial statements. A VIE should be consolidated if a party with an ownership, contractual or other financial interest in the VIE (a variable interest holder) has the power to direct the VIE's most significant activities and the obligation to absorb losses or right to receive benefits of the VIE that could be significant to the VIE. A variable interest holder that consolidates the VIE is called the primary beneficiary. Upon consolidation, the primary beneficiary generally must initially record all of the VIE's assets, liabilities and noncontrolling interests at fair value and subsequently account for the VIE as if it were consolidated. The Company's evaluation of whether it qualifies as the primary beneficiary of a VIE involves significant judgments, estimates and assumptions and includes a qualitative analysis of the activities that most significantly impact the VIE's economic performance and whether the Company has the power to direct those activities, the design of the entity, the rights of the parties and the purpose of the arrangement.
Derivative instruments	Derivative instruments The Company enters into commodity price derivative contracts in order to minimize the price volatility associated with customer natural gas costs at its natural gas distribution segment. These derivatives are not designated as hedging instruments and are recorded in the Consolidated Balance Sheets at fair value. Changes in the fair value of these derivatives along with any contract settlements are recorded each period in regulatory assets or liabilities in accordance with regulatory accounting. The Company does not enter into any derivatives for trading or other speculative purposes.
Leases	Leases Lease liabilities and their corresponding right-of-use assets are recorded based on the present value of lease payments over the expected lease term. The Company recognizes leases with an original lease term of 12 months or less in income on a straight-line basis over the term of the lease and does not recognize a corresponding right-of-use asset or lease liability. The Company determines the lease term based on the non-cancelable and cancelable periods in each contract. The non-cancelable period consists of the term of the contract that is legally enforceable and cannot be canceled by either party without incurring a significant penalty. The cancelable period is determined by various factors that are based on who has the right to cancel a contract. If only the lessor has the right to cancel the contract, the Company will assume the contract will continue. If the lessee is the only party that has the right to cancel the contract, the Company looks to asset, entity and market-based factors. If both the lessor and the lessee have the right to cancel the contract, the Company assumes the contract will not continue. The discount rate used to calculate the present value of the lease liabilities is based upon the implied rate within each contract. If the rate is unknown or cannot be determined, the Company uses an incremental borrowing rate, which is determined by the length of the contract, asset class and the Company's borrowing rates, as of the commencement date of the contract.
Asset retirement obligations	Asset retirement obligations The Company records the fair value of a liability for an asset retirement obligation in the period in which it is incurred. When the liability is initially recorded, the Company capitalizes a cost by increasing the carrying amount of the related long-lived asset. Over time, the liability is accreted to its present value each period and the capitalized cost is depreciated over the useful life of the related asset. Upon settlement of the liability, the Company either settles the obligation for the recorded amount or incurs a gain or loss at its non-regulated operations or incurs a regulatory asset or liability at its regulated operations.
Stock-based compensation	Stock-based compensation The Company determines compensation expense for stock-based awards based on the estimated fair values at the grant date and recognizes the related compensation expense over the vesting period. The Company uses the straight-line amortization method to recognize compensation expense related to RSUs, which only has a service condition. This method recognizes stock compensation expense on a straight-line basis over the requisite service period for the entire award. The Company recognized compensation expense related to PSAs that vest based on performance metrics and service conditions on a straight-line basis over the service period. Inception-to-date expense was adjusted based upon the determination of the potential achievement of the performance target at each reporting date. The Company recognized compensation expense related to PSAs with market-based performance metrics on a straight-line basis over the requisite service period. Outstanding PSAs were converted to RSUs in connection with the completed separation of Knife River through the spinoff. The Company records the compensation expense for PSAs using an estimated forfeiture rate. The estimated forfeiture rate is calculated based on an average of actual historical forfeitures. The Company also performs an analysis of any known factors at the time of the calculation to identify any necessary adjustments to the average historical forfeiture rate. At the time actual forfeitures become more than estimated forfeitures, the Company records compensation expense using actual forfeitures.
Earnings per share	Basic earnings per share is computed by dividing net income by the weighted average number of shares of common stock outstanding during the year. Diluted earnings per share is computed by dividing net income by the total of the weighted average number of shares of common stock outstanding during the year, plus the effect of nonvested performance share awards and restricted stock units.
Income taxes	Income taxes The Company provides deferred federal and state income taxes on all temporary differences between the book and tax basis of the Company's assets and liabilities by using enacted tax rates in effect for the year in which the differences are expected to reverse. The effect of a change in tax rates on deferred tax assets and liabilities is recognized in income in the period that includes the enactment date. Excess deferred income tax balances associated with the Company's rate-regulated activities have been recorded as regulatory liabilities. These regulatory liabilities are expected to be reflected as a reduction in future rates charged to customers in accordance with applicable regulatory procedures. The Company uses the deferral method of accounting for investment tax credits and amortizes the credits on regulated electric and natural gas distribution plant over various periods that conform to the ratemaking treatment prescribed by the applicable state public service commissions.
Income taxes, uncertainties	The Company records uncertain tax positions in accordance with accounting guidance on accounting for income taxes on the basis of a two-step process in which (1) the Company determines whether it is more-likely-than-not that the tax position will be sustained on the basis of the technical merits of the position and (2) for those tax positions that meet the more-likely-than-not recognition threshold, the Company recognizes the largest amount of the tax benefit that is more than 50 percent likely to be realized upon ultimate settlement with the related tax authority. Tax positions that do not meet the more-likely-than-not criteria are reflected as a tax liability. The Company recognizes interest and penalties accrued related to unrecognized tax benefits in income taxes.
Discontinued Operations	As a result of the separations, the historical results of operations are shown in discontinued operations, net of tax, except for allocated general corporate overhead costs of the Company, which did not meet the criteria for discontinued operations. The Company’s consolidated financial statements and accompanying notes for prior periods have been restated. For the comparative periods, Everus' operations are only reflected through October 2024 compared to the full year in 2023 and 2022 and Knife River's operations are only reflected through May 2023 compared to the full year in 2022.
Revenue from Contracts with Customers	Revenue is recognized when a performance obligation is satisfied by transferring control over a product or service to a customer. Revenue is measured based on consideration specified in a contract with a customer and excludes any sales incentives and amounts collected on behalf of third parties. The Company is considered an agent for certain taxes collected from customers. As such, the Company presents revenues net of these taxes at the time of sale to be remitted to governmental authorities, including sales and use taxes. As part of the adoption of ASC 606 - Revenue from Contracts with Customers , the Company elected the practical expedient to recognize the incremental costs of obtaining a contract as an expense when incurred if the amortization period of the asset that the Company otherwise would have recognized is 12 months or less.
Environmental Allowances and Obligations	Environmental Allowances and Obligations Beginning in 2023, the Company's natural gas distribution segment acquires environmental allowances as part of its requirement to comply with environmental regulations in certain states. Allowances are allocated by the respective states to the Company at no cost and additional allowances are required to be purchased as needed based on the requirements in the respective states. The segment records purchased and allocated environmental allowances at weighted average cost under the inventory method of accounting. Environmental allowances are included in Prepayments and other current assets and noncurrent assets - Other on the Consolidated Balance Sheets. Environmental compliance obligations, which are based on GHG emissions, are measured at the carrying value of environmental allowances held plus the estimated value of additional allowances necessary to satisfy the compliance obligation. Environmental compliance obligations are included in current liabilities - Other accrued liabilities and noncurrent liabilities - Other on the Consolidated Balance Sheets. The Company recognizes revenue from the sale of emissions allowances allocated under the environmental programs when the allowances are sold at auction. The revenues associated with the sale of these allowances are deferred as a component of the respective jurisdiction’s regulatory liability for environmental compliance. As environmental allowances are surrendered, the segment reduces the associated environmental compliance assets and liabilities from the Consolidated Balance Sheets. The expenses and revenues associated with the Company’s environmental allowances and obligations are deferred as regulatory assets and liabilities and recognized as a component of purchased natural gas sold as recovered in customer rates. For more information on the Company’s regulatory assets and liabilities, see Note 6.
Accumulated Other Comprehensive Loss	The Company's accumulated other comprehensive loss is comprised of losses on derivative instruments qualifying as hedges, postretirement liability adjustments and gain (loss) on available-for-sale investments.
Business Segment Data	The Company's reportable segments are those that are based on the Company's method of internal reporting, which generally segregates the strategic business activities due to differences in products, services and regulation. The internal reporting of these operating segments is defined based on the reporting and review process used by the Company's CODM, the chief executive officer.
Commitments and Contingencies	The Company is party to claims and lawsuits arising out of its business and that of its consolidated subsidiaries, which may include, but are not limited to, matters involving property damage, personal injury, and environmental, contractual, statutory and regulatory obligations. The Company accrues a liability for those contingencies when the incurrence of a loss is probable and the amount can be reasonably estimated. If a range of amounts can be reasonably estimated and no amount within the range is a better estimate than any other amount, then the minimum of the range is accrued. The Company does not accrue liabilities when the likelihood that the liability has been incurred is probable but the amount cannot be reasonably estimated or when the liability is believed to be only reasonably possible or remote. For contingencies where an unfavorable outcome is probable or reasonably possible and which are material, the Company discloses the nature of the contingency and, in some circumstances, an estimate of the possible loss. Accruals are based on the best information available, but in certain situations management is unable to estimate an amount or range of a reasonably possible loss including, but not limited to when: (1) the damages are unsubstantiated or indeterminate, (2) the proceedings are in the early stages, (3) numerous parties are involved, or (4) the matter involves novel or unsettled legal theories.

Significant Accounting Polici_3

Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2024
Accounting Policies [Abstract]
Schedule of Expected Credit Loss	Details of the Company's expected credit losses were as follows: Electric Natural gas Pipeline Total (In thousands) At December 31, 2022 $ 375 $ 1,615 $ 2 $ 1,992 Current expected credit loss provision 1,645 5,777 — 7,422 Less write-offs charged against the allowance 1,994 7,355 2 9,351 Credit loss recoveries collected 388 1,152 — 1,540 At December 31, 2023 414 1,189 — 1,603 Current expected credit loss provision 1,891 4,667 — 6,558 Less write-offs charged against the allowance 2,218 5,709 — 7,927 Credit loss recoveries collected 386 1,219 — 1,605 At December 31, 2024 $ 473 $ 1,366 $ — $ 1,839
Schedule of Inventory	Inventories at December 31 consisted of: 2024 2023 (In thousands) Natural gas in storage (current) $ 40,073 $ 39,377 Fuel stock 4,867 5,307 Total $ 44,940 $ 44,684
Schedule of Property, Plant and Equipment	The amount of AFUDC for the years ended December 31 was as follows: 2024 2023 2022 (In thousands) AFUDC - borrowed $ 10,964 $ 10,035 $ 2,236 AFUDC - equity $ 2,251 $ 1,894 $ 2,165
Schedule of Earnings Per Share Reconciliation	A reconciliation of the weighted average common shares outstanding used in the basic and diluted earnings per share calculations follows: 2024 2023 2022 (In thousands, except per share amounts) Weighted average common shares outstanding - basic 203,867 203,640 203,358 Effect of dilutive performance share awards 786 298 104 Weighted average common shares outstanding - diluted 204,653 203,938 203,462 Earnings per share - basic: Income from continuing operations $ .89 $ 1.62 $ .58 Discontinued operations, net of tax .49 .42 1.23 Earnings per share - basic $ 1.38 $ 2.04 $ 1.81 Earnings per share - diluted: Income from continuing operations $ .88 $ 1.62 $ .58 Discontinued operations, net of tax .49 .41 1.23 Earnings per share - diluted $ 1.37 $ 2.03 $ 1.81 Shares excluded from the calculation of diluted earnings per share — — 14 Dividends declared per common share $ .5100 $ .6950 $ .8750

Discontinued Operations (Tables

Discontinued Operations (Tables)	12 Months Ended
	Dec. 31, 2024
Discontinued Operations and Disposal Groups [Abstract]
Schedule of Disposal Groups, Including Discontinued Operations	The carrying amounts of the major classes of assets and liabilities related to the discontinued operations of Everus included in the Company’s Consolidated Balance Sheet at December 31, 2023 were as follows: December 31, 2023 Assets (In Thousands) Current assets: Cash and cash equivalents $ 16,501 Receivables, net 692,629 Inventories 42,709 Prepayments and other current assets 17,651 Total current assets of discontinued operations 769,490 Noncurrent assets: Net property, plant and equipment 116,018 Goodwill 143,224 Other intangible assets, net 2,004 Investments 11,760 Operating lease right-of-use assets 53,232 Other 21,627 Total noncurrent assets of discontinued operations 347,865 Total assets of discontinued operations $ 1,117,355 Liabilities Current liabilities: Accounts payable $ 315,240 Taxes payable 8,557 Accrued compensation 44,721 Operating lease liabilities due within one year 21,143 Other accrued liabilities 53,619 Total current liabilities of discontinued operations 443,280 Noncurrent liabilities: Long-term debt 132,000 Deferred income taxes 6,212 Operating lease liabilities 32,504 Other 8,934 Total noncurrent liabilities of discontinued operations 179,650 Total liabilities of discontinued operations $ 622,930 The reconciliation of the major classes of income and expense constituting pretax income from discontinued operations to the after-tax income from discontinued operations on the Consolidated Statements of Income were as follows: 2024 2023 2022 (In thousands) Operating revenues $ 2,377,332 $ 3,589,251 $ 5,226,766 Operating expenses 2,241,162 3,422,393 4,853,408 Operating (loss) income 136,170 166,858 373,358 Other income (expense) 12,446 10,599 4,119 Interest expense 7,118 47,229 38,590 Income from discontinued operations before income taxes 141,498 130,228 338,887 Income taxes 41,463 45,638 88,650 Discontinued operations, net of tax $ 100,035 $ 84,590 $ 250,237

Revenue from Contracts with C_2

Revenue from Contracts with Customers (Tables)	12 Months Ended
	Dec. 31, 2024
Revenue from Contract with Customer [Abstract]
Schedule of Disaggregation of Revenue	Disaggregation In the following table, revenue is disaggregated by the type of customer or service provided. The Company believes this level of disaggregation best depicts how the nature, amount, timing and uncertainty of revenue and cash flows are affected by economic factors. The table also includes a reconciliation of the disaggregated revenue by reportable segments. For more information on the Company's business segments, see Note 17. Year ended December 31, 2024 Electric Natural gas distribution Pipeline Other Total (In thousands) Residential utility sales $ 140,054 $ 646,049 $ — $ — $ 786,103 Commercial utility sales 171,760 399,087 — — 570,847 Industrial utility sales 42,883 42,588 — — 85,471 Other utility sales 7,910 — — — 7,910 Natural gas transportation — 60,645 174,623 — 235,268 Natural gas storage — — 23,690 — 23,690 Other 59,288 40,703 13,139 195 113,325 Intersegment eliminations (72) (130) (69,222) (195) (69,619) Revenues from contracts with customers 421,823 1,188,942 142,230 — 1,752,995 Other revenues (7,417) 12,033 367 — 4,983 Total external operating revenues $ 414,406 $ 1,200,975 $ 142,597 $ — $ 1,757,978 Year ended December 31, 2023 Electric Natural gas distribution Pipeline Other Total (In thousands) Residential utility sales $ 136,274 $ 724,600 $ — $ — $ 860,874 Commercial utility sales 170,321 442,507 — — 612,828 Industrial utility sales 43,063 45,205 — — 88,268 Other utility sales 7,270 — — — 7,270 Natural gas transportation — 52,465 145,297 — 197,762 Natural gas storage — — 18,254 — 18,254 Other 54,508 15,141 13,874 119 83,642 Intersegment eliminations (138) (301) (62,533) (119) (63,091) Revenues from contracts with customers 411,298 1,279,617 114,892 — 1,805,807 Other revenues (10,261) 7,619 187 — (2,455) Total external operating revenues $ 401,037 $ 1,287,236 $ 115,079 $ — $ 1,803,352 Year ended December 31, 2022 Electric Natural gas distribution Pipeline Other Total (In thousands) Residential utility sales $ 138,634 $ 718,191 $ — $ — $ 856,825 Commercial utility sales 146,182 453,802 — — 599,984 Industrial utility sales 43,766 41,710 — — 85,476 Other utility sales 7,597 — — — 7,597 Natural gas transportation — 48,886 129,290 — 178,176 Natural gas storage — — 14,583 — 14,583 Other 45,608 13,617 11,450 86 70,761 Intersegment eliminations (58) (216) (58,884) (86) (59,244) Revenues from contracts with customers 381,729 1,275,990 96,439 — 1,754,158 Other revenues (4,714) (2,402) 256 — (6,860) Total external operating revenues $ 377,015 $ 1,273,588 $ 96,695 $ — $ 1,747,298

Property, Plant and Equipment (

Property, Plant and Equipment (Tables)	12 Months Ended
	Dec. 31, 2024
Property, Plant and Equipment [Abstract]
Schedule of Property, Plant and Equipment	Property, plant and equipment at December 31 was as follows: 2024 2023 Weighted (Dollars in thousands, where applicable) Electric: Generation $ 1,014,906 $ 939,474 49 Distribution 546,121 521,215 47 Transmission 662,466 639,999 65 CWIP 81,316 115,103 0 Other 176,007 153,248 15 Natural gas distribution: Distribution 2,955,435 2,771,540 53 Transmission 146,710 115,057 56 Storage 43,700 42,654 37 General 229,034 215,572 13 CWIP 74,207 70,373 0 Other 282,007 246,991 15 Pipeline: Transmission 1,173,259 1,035,995 46 Storage 61,369 57,160 53 CWIP 29,629 57,038 0 Other 73,749 68,194 17 Other: Land and other 4,148 31,654 7 Less accumulated depreciation and amortization 2,209,771 2,076,375 Net property, plant and equipment $ 5,344,292 $ 5,004,892

Regulatory Assets and Liabili_2

Regulatory Assets and Liabilities (Tables)	12 Months Ended
	Dec. 31, 2024
Regulatory Assets and Liabilities Disclosure [Abstract]
Schedule of Regulatory Assets	The following table summarizes the individual components of unamortized regulatory assets and liabilities as of December 31: Estimated Recovery or Refund Period * 2024 2023 (In thousands) Regulatory assets: Current: Natural gas costs recoverable through rate adjustments Up to 1 year $ 91,091 $ 98,844 Environmental compliance programs Up to 1 year 76,964 5,525 Conservation programs Up to 1 year 19,123 14,425 Electric fuel and purchased power deferral Up to 1 year 9,662 33,918 Decoupling mechanisms Up to 1 year 6,767 — Cost recovery mechanisms Up to 1 year 5,114 9,153 Other Up to 1 year 6,715 10,627 215,436 172,492 Noncurrent: Pension and postretirement benefits ** 142,064 142,511 Cost recovery mechanisms Up to 24 years 76,542 85,944 Plant costs/asset retirement obligations Over plant lives 47,042 46,009 Manufactured gas plant site remediation - 27,964 26,127 Taxes recoverable from customers Over plant lives 12,221 12,249 Electric fuel and purchased power deferral Up to 2 years 4,349 — Covid-19 deferred costs - 4,167 2,746 Long-term debt refinancing costs Up to 36 years 2,011 2,600 Environmental compliance programs - — 66,806 Natural gas costs recoverable through rate adjustments Up to 2 years — 55,493 Other Up to 14 years 5,990 6,614 322,350 447,099 Total regulatory assets $ 537,786 $ 619,591 Regulatory liabilities: Current: Environmental compliance Up to 1 year $ 72,387 $ — Natural gas costs refundable through rate adjustments Up to 1 year 45,427 43,161 Margin sharing Up to 1 year 4,156 5,243 Provision for rate refund Up to 1 year 3,677 6,866 Taxes refundable to customers Up to 1 year 2,163 2,149 Conservation programs Up to 1 year 2,082 2,130 Cost recovery mechanisms Up to 1 year 1,720 6,284 Other Up to 1 year 5,555 4,928 137,167 70,761 Noncurrent: Plant removal and decommissioning costs Over plant lives 217,603 220,147 Taxes refundable to customers Over plant lives 185,402 193,578 Cost recovery mechanisms Up to 17 years 30,354 21,791 Accumulated deferred investment tax credit Over plant lives 18,788 15,740 Pension and postretirement benefits ** 4,862 6,044 Environmental compliance programs - — 61,941 Other Up to 13 years 2,161 1,809 459,170 521,050 Total regulatory liabilities $ 596,337 $ 591,811 Net regulatory position $ (58,551) $ 27,780 * Estimated recovery or refund period for amounts currently being recovered or refunded in rates to customers. ** Recovered as expense is incurred or cash contributions are made.
Schedule of Regulatory Liabilities	The following table summarizes the individual components of unamortized regulatory assets and liabilities as of December 31: Estimated Recovery or Refund Period * 2024 2023 (In thousands) Regulatory assets: Current: Natural gas costs recoverable through rate adjustments Up to 1 year $ 91,091 $ 98,844 Environmental compliance programs Up to 1 year 76,964 5,525 Conservation programs Up to 1 year 19,123 14,425 Electric fuel and purchased power deferral Up to 1 year 9,662 33,918 Decoupling mechanisms Up to 1 year 6,767 — Cost recovery mechanisms Up to 1 year 5,114 9,153 Other Up to 1 year 6,715 10,627 215,436 172,492 Noncurrent: Pension and postretirement benefits ** 142,064 142,511 Cost recovery mechanisms Up to 24 years 76,542 85,944 Plant costs/asset retirement obligations Over plant lives 47,042 46,009 Manufactured gas plant site remediation - 27,964 26,127 Taxes recoverable from customers Over plant lives 12,221 12,249 Electric fuel and purchased power deferral Up to 2 years 4,349 — Covid-19 deferred costs - 4,167 2,746 Long-term debt refinancing costs Up to 36 years 2,011 2,600 Environmental compliance programs - — 66,806 Natural gas costs recoverable through rate adjustments Up to 2 years — 55,493 Other Up to 14 years 5,990 6,614 322,350 447,099 Total regulatory assets $ 537,786 $ 619,591 Regulatory liabilities: Current: Environmental compliance Up to 1 year $ 72,387 $ — Natural gas costs refundable through rate adjustments Up to 1 year 45,427 43,161 Margin sharing Up to 1 year 4,156 5,243 Provision for rate refund Up to 1 year 3,677 6,866 Taxes refundable to customers Up to 1 year 2,163 2,149 Conservation programs Up to 1 year 2,082 2,130 Cost recovery mechanisms Up to 1 year 1,720 6,284 Other Up to 1 year 5,555 4,928 137,167 70,761 Noncurrent: Plant removal and decommissioning costs Over plant lives 217,603 220,147 Taxes refundable to customers Over plant lives 185,402 193,578 Cost recovery mechanisms Up to 17 years 30,354 21,791 Accumulated deferred investment tax credit Over plant lives 18,788 15,740 Pension and postretirement benefits ** 4,862 6,044 Environmental compliance programs - — 61,941 Other Up to 13 years 2,161 1,809 459,170 521,050 Total regulatory liabilities $ 596,337 $ 591,811 Net regulatory position $ (58,551) $ 27,780 * Estimated recovery or refund period for amounts currently being recovered or refunded in rates to customers. ** Recovered as expense is incurred or cash contributions are made.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2024
Fair Value Disclosures [Abstract]
Schedule of Debt Securities, Available-for-sale	Details of available-for-sale securities were as follows: December 31, 2024 Cost Gross Gross Fair Value (In thousands) Mortgage-backed securities $ 7,933 $ 4 $ 383 $ 7,554 U.S. Treasury securities 3,945 80 1 4,024 Total $ 11,878 $ 84 $ 384 $ 11,578 December 31, 2023 Cost Gross Gross Fair Value (In thousands) Mortgage-backed securities $ 8,234 $ 17 $ 470 $ 7,781 U.S. Treasury securities 3,521 28 8 3,541 Total $ 11,755 $ 45 $ 478 $ 11,322
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis	The Company's assets measured at fair value on a recurring basis were as follows: Fair Value Measurements at December 31, 2024, Using Quoted Prices Significant Significant Balance at December 31, 2024 (In thousands) Assets: Money market funds $ — $ 12,879 $ — $ 12,879 Insurance contracts* — 59,282 — 59,282 Available-for-sale securities: Mortgage-backed securities — 7,554 — 7,554 U.S. Treasury securities — 4,024 — 4,024 Total assets measured at fair value $ — $ 83,739 $ — $ 83,739 * The insurance contracts invest approximately 58 percent in fixed-income investments, 17 percent in common stock of large-cap companies, 8 percent in target date investments, 8 percent in common stock of mid-cap companies, 4 percent in common stock of small-cap companies, 4 percent in cash equivalents, and 1 percent in international investments. Fair Value Measurements at December 31, 2023, Using Quoted Prices Significant Significant Balance at December 31, 2023 (In thousands) Assets: Money market funds $ — $ 6,409 $ — $ 6,409 Insurance contracts* — 62,936 — 62,936 Available-for-sale securities: Mortgage-backed securities — 7,781 — 7,781 U.S. Treasury securities — 3,541 — 3,541 Total assets measured at fair value $ — $ 80,667 $ — $ 80,667 * The insurance contracts invest approximately 60 percent in fixed-income investments, 15 percent in common stock of large-cap companies, 8 percent in target date investments, 7 percent in common stock of mid-cap companies, 5 percent in common stock of small-cap companies, 3 percent in cash equivalents, 1 percent in high yield investments, and 1 percent in international investments.
Schedule of Fair Value, by Balance Sheet Grouping	The estimated fair value of the Company's Level 2 long-term debt at December 31 was as follows: 2024 2023 (In thousands) Carrying Amount $ 2,292,610 $ 2,166,223 Fair Value $ 1,963,396 $ 1,914,039

Debt (Tables)

Debt (Tables)	12 Months Ended
	Dec. 31, 2024
Debt Disclosure [Abstract]
Schedule of Line of Credit Facilities	The following table summarizes the outstanding revolving credit facilities of the Company and its subsidiaries: Company Facility Facility Amount Outstanding at December 31, 2024 Amount Outstanding at December 31, 2023 Letters of Credit at December 31, 2024 Expiration (In millions) Montana-Dakota Utilities Co. Commercial paper/Revolving credit agreement (a) $ 200.0 $ 81.4 $ 144.2 $ — 10/18/28 Cascade Natural Gas Corporation Revolving credit agreement $ 175.0 (b) $ 64.6 $ 15.4 $ 2.2 (c) 6/20/29 Intermountain Gas Company Revolving credit agreement $ 175.0 (b) $ 105.1 $ 30.7 $ — 6/20/29 MDU Resources Group, Inc. Revolving credit agreement $ 200.0 (d) $ — $ — $ 12.1 (c) 5/31/28 (a) The commercial paper program is supported by a revolving credit agreement with various banks (provisions allow for increased borrowings, at the option of Montana-Dakota on stated conditions, up to a maximum of $250.0 million). At December 31, 2024 and 2023, there were no amounts outstanding under the revolving credit agreement. (b) Certain provisions allow for increased borrowings, up to a maximum of $225.0 million. (c) Outstanding letter(s) of credit reduce the amount available under the credit agreement. (d) Certain provisions allow for increased borrowings, up to a maximum of $250.0 million.
Schedule of Long-Term Debt	Long-term debt outstanding was as follows: Weighted Average Interest Rate at December 31, 2024 2024 2023 (In thousands) Senior notes due on dates ranging from August 23, 2025 to June 15, 2062 4.57 % $ 1,947,000 $ 1,882,000 Credit agreements due on June 20, 2029 5.79 % 169,700 46,100 Commercial paper supported by revolving credit agreement 4.76 % 81,400 144,200 Term loan agreements due on dates ranging from September 3, 2032 to April 1, 2039 4.44 % 65,600 64,300 Medium-term notes due on dates ranging from September 15, 2027 to March 16, 2029 7.32 % 35,000 35,000 Other notes due on dates ranging from May 31, 2028 to November 30, 2038 6.00 % 346 980 Less unamortized debt issuance costs 6,436 6,357 Total long-term debt 2,292,610 2,166,223 Less current maturities 161,700 61,319 Net long-term debt $ 2,130,910 $ 2,104,904
Schedule of Maturities of Long-Term Debt	Long-term debt maturities, which excludes unamortized debt issuance costs and discount, for the five years and thereafter following December 31, 2024, were as follows: 2025 2026 2027 2028 2029 Thereafter (In thousands) Long-term debt maturities $ 161,700 $ 144,700 $ 24,700 $ 161,100 $ 244,400 $ 1,562,446

Asset Retirement Obligations (T

Asset Retirement Obligations (Tables)	12 Months Ended
	Dec. 31, 2024
Asset Retirement Obligation [Abstract]
Schedule of Change in Asset Retirement Obligation	A reconciliation of the Company's liability, which the current portion is included in other accrued liabilities on the Consolidated Balance Sheets, for the years ended December 31 was as follows: 2024 2023 (In thousands) Balance at beginning of year $ 385,154 $ 373,147 Liabilities incurred 2,721 533 Liabilities settled (5,271) (6,633) Accretion expense* 19,655 18,894 Revisions in estimates 4,388 (787) Balance at end of year $ 406,647 $ 385,154 * Includes $19.6 million and $18.9 million in 2024 and 2023, respectively, recorded to regulatory assets.

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2024
Share-Based Payment Arrangement [Abstract]
Schedule of Target Grants of Restricted Stock Units	Target grants of RSUs outstanding at December 31, 2024, were as follows: Grant Date Performance Period Target Grant of Shares February 2023/ July 2023 2023-2025 542,233 February 2024/ June 2024 2024-2026 698,284 A summary of the status of the RSUs for the year ended December 31, 2024, was as follows: RSUs Number of Shares Weighted ** Nonvested at beginning of period 873,300 $ 21.16 Granted pre-separation of Everus 478,938 20.89 Forfeited (112,826) 21.35 Non-vested pre-separation of Everus 1,239,412 Adjustments related to the Everus separation* 663,661 Vested shares (662,556) 12.04 Nonvested at end of period 1,240,517 $ 12.56 * Includes the conversion adjustments to preserve the intrinsic value of the awards and the cancellation of outstanding awards held by employees that transferred to Everus, which were replaced with awards issued by Everus as part of the separation. ** Weighted average grant-date fair values post-separation of Everus reflects incremental fair value related to modifying the awards and the Company's adjusted stock price due to the separation.
Schedule of Share-Based Payment Award, Performance Shares, Valuation Assumptions	Assumptions used for initial grants applicable to the market condition for certain PSAs issued in 2022 were: 2022 Weighted average grant-date fair value $36.25 Blended volatility range 24.07% - 31.41% Risk-free interest rate range .71% - 1.68% Weighted average discounted dividends per share $2.93

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Loss (Tables)	12 Months Ended
	Dec. 31, 2024
Equity [Abstract]
Schedule of Accumulated Other Comprehensive Income (Loss)	The after-tax changes in the components of accumulated other comprehensive loss were as follows: Net Post- Net Total (In thousands) At December 31, 2022 $ (125) $ (29,900) $ (558) $ (30,583) Other comprehensive income (loss) before reclassifications — (646) 173 (473) Amounts reclassified from accumulated other comprehensive loss 81 242 43 366 Net current-period other comprehensive income (loss) 81 (404) 216 (107) Amounts reclassified related to the separation of Knife River 44 12,262 — 12,306 At December 31, 2023 — (18,042) (342) (18,384) Other comprehensive income before reclassifications — 1,049 85 1,134 Amounts reclassified from accumulated other comprehensive loss — 432 20 452 Net current-period other comprehensive income — 1,481 105 1,586 At December 31, 2024 $ — $ (16,561) $ (237) $ (16,798)
Schedule of Reclassification Out of AOCI	The following amounts were reclassified out of accumulated other comprehensive loss into net income. The amounts presented in parentheses indicate a decrease to net income on the Consolidated Statements of Income. The reclassifications for the years ended December 31 were as follows: 2024 2023 Location on Consolidated (In thousands) Reclassification adjustment for loss on derivative instruments included in net income $ — $ (96) Interest expense — 15 Income taxes — (81) Amortization of postretirement liability losses included in net periodic benefit credit (577) (320) Other income 145 78 Income taxes (432) (242) Reclassification adjustment on available-for-sale investments included in net income (25) (54) Other income 5 11 Income taxes (20) (43) Total reclassifications $ (452) $ (366)

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2024
Income Tax Disclosure [Abstract]
Schedule of Income before Income Tax, Domestic and Foreign	The components of income before income taxes from continuing operations for each of the years ended December 31 were as follows: 2024 2023 2022 (In thousands) United States $ 198,662 $ 340,330 $ 123,447 Income before income taxes from continuing operations $ 198,662 $ 340,330 $ 123,447
Schedule of Components of Income Tax Expense (Benefit)	Income tax expense (benefit) from continuing operations for the years ended December 31 was as follows: 2024 2023 2022 (In thousands) Current: Federal $ 30,412 $ 8,271 $ (15,849) State 3,255 3,251 1,857 33,667 11,522 (13,992) Deferred: Income taxes: Federal (17,321) (3,331) 15,038 State (1,805) (125) 4,251 Investment tax credit - net 3,048 2,147 898 (16,078) (1,309) 20,187 Total income tax expense $ 17,589 $ 10,213 $ 6,195
Schedule of Deferred Tax Assets and Liabilities	Components of deferred tax assets and deferred tax liabilities at December 31 were as follows: 2024 2023 (In thousands) Deferred tax assets: Environmental compliance $ 33,730 $ 28,873 Pension and postretirement 25,508 27,584 Compensation-related 15,651 17,106 Customer advances 9,719 8,312 Cost recovery mechanisms 7,402 5,314 Legal and environmental contingencies 5,317 4,881 Other 20,386 13,045 Total deferred tax assets 117,713 105,115 Deferred tax liabilities: Basis differences on property, plant and equipment 426,493 404,039 Pension and postretirement 48,355 39,110 Purchased gas adjustment 20,441 34,618 Environmental compliance 17,260 16,221 Cost recovery mechanisms 19,245 22,604 Legal and environmental contingencies 6,300 5,902 Other 19,931 33,947 Total deferred tax liabilities 558,025 556,441 Valuation allowance 1,008 1,010 Net deferred income tax liability $ 441,320 $ 452,336
Schedule of Change in Net Deferred Income Tax Liability Reconciliation	The following table reconciles the change in the net deferred income tax liability from December 31, 2023, to December 31, 2024, to deferred income tax expense: 2024 (In thousands) Change in net deferred income tax liability from the preceding table $ (11,016) Excess deferred income tax amortization (8,121) Deferred taxes associated with other comprehensive income (532) Other 3,591 Deferred income tax expense for the period $ (16,078)
Schedule of Effective Income Tax Rate Reconciliation	Total income tax expense differs from the amount computed by applying the statutory federal income tax rate to income before taxes. The reasons for this difference were as follows: Years ended December 31, 2024 2023 2022 Amount % Amount % Amount % (Dollars in thousands) Computed tax at federal statutory rate $ 41,719 21.0 $ 71,469 21.0 $ 25,924 21.0 Increases (reductions) resulting from: State income taxes, net of federal income tax 4,047 2.0 3,605 1.1 2,484 2.0 State investment tax credit, net of federal income tax 2,400 1.2 1,545 .5 1,624 1.3 Executive compensation 2,111 1.1 564 .2 683 .6 Federal renewable energy credit (16,871) (8.5) (15,175) (4.5) (15,343) (12.4) Excess deferred income tax amortization (8,121) (4.1) (8,383) (2.5) (9,008) (7.3) State tax rate change (2,317) (1.2) (9) — (3) — Research and development tax credit (1,465) (.7) (1,985) (.6) (1,692) (1.4) Nonqualified benefit plans (1,142) (.6) (1,313) (.4) 1,516 1.2 Tax-free debt for equity exchange — — (38,967) (11.4) — — Other (2,772) (1.4) (1,138) (.3) 10 — Total income tax expense $ 17,589 8.8 $ 10,213 3.1 $ 6,195 5.0

Cash Flow Information (Tables)

Cash Flow Information (Tables)	12 Months Ended
	Dec. 31, 2024
Supplemental Cash Flow Information [Abstract]
Schedule of Cash Flow, Supplemental Disclosures	Cash expenditures for interest and income taxes for the years ended December 31 were as follows: 2024 2023 2022 (In thousands) Interest, net* $ 108,242 $ 112,839 $ 49,036 Income taxes paid (refunded), net** $ 43,572 $ 12,162 $ (27,884) * AFUDC - borrowed was $11.0 million, $10.0 million and $2.2 million for the years ended December 31, 2024, 2023 and 2022, respectively. ** Income taxes paid, including discontinued operations, were $80.9 million, $62.5 million and $26.4 million for the years ended December 31, 2024, 2023 and 2022, respectively. Noncash investing and financing transactions at December 31 were as follows: 2024 2023 2022 (In thousands) Property, plant and equipment additions in accounts payable $ 36,820 $ 46,364 $ 34,886 Right-of-use assets obtained in exchange for new operating lease liabilities $ 1,787 $ 2,265 $ 1,324 Debt for equity exchange of retained shares in Knife River $ — $ 293,239 $ —

Business Segment Data (Tables)

Business Segment Data (Tables)	12 Months Ended
	Dec. 31, 2024
Segment Reporting [Abstract]
Schedule of Segment Reporting Information, by Segment	Information on the Company's segments as of December 31 and for the years then ended was as follows: Year ended December 31, 2024 Electric Natural gas distribution Pipeline Other Consolidated (In thousands) Operating revenues: External operating revenues $ 414,406 $ 1,200,975 $ 142,597 $ — $ 1,757,978 Intersegment operating revenues 72 130 69,222 195 69,619 Operation and maintenance: External operation and maintenance 94,897 231,087 75,456 13,051 414,491 Intersegment operation and maintenance 72 130 324 195 721 Purchased natural gas sold: External purchased natural gas sold — 630,403 — — 630,403 Intersegment purchased natural gas sold — 68,898 — — 68,898 Electric fuel and purchased power 141,148 — — — 141,148 Depreciation and amortization 66,524 101,958 29,362 2,234 200,078 Taxes, other than income 17,605 76,042 12,175 394 106,216 Other income: External other income 8,205 25,509 5,850 1,803 41,367 Intersegment other income — — 655 14,798 15,453 Interest expense: External interest expense 30,058 63,185 10,862 4,242 108,347 Intersegment interest expense — — 4,633 10,820 15,453 Income tax expense (benefit) (2,414) 7,974 17,470 (5,441) 17,589 Income (loss) from continuing operations 74,793 46,937 68,042 (8,699) 181,073 Discontinued operations, net of tax — — — 100,035 100,035 Net income $ 74,793 $ 46,937 $ 68,042 $ 91,336 $ 281,108 Capital expenditures (a) $ 110,812 $ 286,152 $ 126,806 $ 1,728 $ 525,498 Assets $ 1,976,912 (b) $ 3,730,532 (b) $ 1,151,317 $ 180,057 (c) $ 7,038,818 Property, plant and equipment $ 2,480,816 (b) $ 3,731,093 (b) $ 1,338,006 $ 4,148 $ 7,554,063 Accumulated depreciation and amortization $ 716,736 (b) $ 1,139,223 (b) $ 351,045 $ 2,767 $ 2,209,771 (a) Capital expenditures include noncash transactions such as capital expenditure-related accounts payable and AFUDC totaling $7.1 million. (b) Includes allocations of common utility property for the Electric and Natural gas distribution segments. (c) Other includes assets not directly assignable to a business (i.e. cash, cash equivalents and restricted cash, certain accounts receivable, certain investments and other miscellaneous current and deferred assets). Year ended December 31, 2023 Electric Natural gas distribution Pipeline Other Consolidated (In thousands) Operating revenues: External operating revenues $ 401,037 $ 1,287,236 $ 115,079 $ — $ 1,803,352 Intersegment operating revenues 138 301 62,533 119 63,091 Operation and maintenance: External operation and maintenance 92,521 219,481 70,386 24,693 407,081 Intersegment operation and maintenance 138 301 431 119 989 Purchased natural gas sold: External purchased natural gas sold — 742,965 — — 742,965 Intersegment purchased natural gas sold — 62,102 — — 62,102 Electric fuel and purchased power 134,779 — — — 134,779 Depreciation and amortization 64,253 95,300 26,811 4,086 190,450 Taxes, other than income 16,695 75,207 10,822 409 103,133 Realized gain on tax-free exchange of the retained shares in Knife River — — — 186,556 186,556 Other income: External other income 5,815 20,867 3,675 3,097 33,454 Intersegment other income — — 217 13,431 13,648 Interest expense: External interest expense 28,064 57,601 9,428 9,531 104,624 Intersegment interest expense — — 3,842 9,806 13,648 Income tax expense (benefit) (1,019) 6,927 12,409 (8,104) 10,213 Income from continuing operations 71,559 48,520 47,375 162,663 330,117 Discontinued operations, net of tax — — (457) 85,047 84,590 Net income $ 71,559 $ 48,520 $ 46,918 $ 247,710 $ 414,707 Capital expenditures (a) $ 109,805 $ 274,836 $ 115,903 $ (2,825) $ 497,719 Assets $ 1,955,644 (b) $ 3,532,142 (b) $ 1,045,704 $ 1,299,669 (c) $ 7,833,159 Property, plant and equipment $ 2,369,039 (b) $ 3,462,187 (b) $ 1,218,387 $ 31,654 $ 7,081,267 Accumulated depreciation and amortization $ 660,438 (b) $ 1,068,037 (b) $ 328,010 $ 19,890 $ 2,076,375 (a) Capital expenditures include noncash transactions such as capital expenditure-related accounts payable and AFUDC totaling $(13.6) million. (b) Includes allocations of common utility property for the Electric and Natural gas distribution segments. (c) Other includes assets of discontinued operations and assets not directly assignable to a business (i.e. cash, cash equivalents and restricted cash, certain accounts receivable, certain investments and other miscellaneous current and deferred assets). Year ended December 31, 2022 Electric Natural gas distribution Pipeline Other Consolidated (In thousands) Operating revenues: External operating revenues $ 377,015 $ 1,273,588 $ 96,695 $ — $ 1,747,298 Intersegment operating revenues 58 216 58,884 86 59,244 Operation and maintenance: External operation and maintenance 93,236 205,009 60,300 21,406 379,951 Intersegment operation and maintenance 58 216 638 86 998 Purchased natural gas sold: External purchased natural gas sold — 757,883 — — 757,883 Intersegment purchased natural gas sold — 58,246 — — 58,246 Electric fuel and purchased power 119,405 — — — 119,405 Depreciation and amortization 67,802 89,466 26,857 4,435 188,560 Taxes, other than income 16,917 71,095 12,318 299 100,629 Other income: External other income 528 3,213 1,272 (1,753) 3,260 Intersegment other income — — 80 556 636 Interest expense: External interest expense 28,526 42,126 9,966 65 80,683 Intersegment interest expense — — 136 500 636 Income tax expense (benefit) (5,420) 7,805 10,522 (6,712) 6,195 Income (loss) from continuing operations 57,077 45,171 36,194 (21,190) 117,252 Discontinued operations, net of tax — — (906) 251,143 250,237 Net income $ 57,077 $ 45,171 $ 35,288 $ 229,953 $ 367,489 Capital expenditures (a) $ 133,970 $ 240,064 $ 61,923 $ 2,272 $ 438,229 Assets $ 1,856,258 (b) $ 3,214,452 (b) $ 961,893 $ 3,628,178 (c) $ 9,660,781 Property, plant and equipment $ 2,276,613 (b) $ 3,208,059 (b) $ 1,108,141 $ 36,705 $ 6,629,518 Accumulated depreciation and amortization $ 625,813 (b) $ 1,009,788 (b) $ 308,516 $ 19,143 $ 1,963,260 (a) Capital expenditures include noncash transactions such as capital expenditure-related accounts payable and AFUDC totaling $4.4 million. (b) Includes allocations of common utility property for the Electric and Natural gas distribution segments. (c) Other includes assets of discontinued operations and assets not directly assignable to a business (i.e. cash, cash equivalents and restricted cash, certain accounts receivable, certain investments and other miscellaneous current and deferred assets).
Schedule of Reconciliation of Revenue from Segments to Consolidated	A reconciliation of reportable segment operating revenues and assets to consolidated operating revenues and assets is as follows: 2024 2023 2022 (In thousands) Operating revenues reconciliation: Total reportable segment operating revenues $ 1,827,402 $ 1,866,324 $ 1,806,456 Other revenue 195 119 86 Elimination of intersegment operating revenues (69,619) (63,091) (59,244) Total consolidated operating revenues $ 1,757,978 $ 1,803,352 $ 1,747,298 Asset reconciliation: Total reportable segment assets $ 6,892,959 $ 6,564,962 $ 6,061,151 Other assets 525,258 1,847,432 4,784,142 Elimination of intersegment receivables (379,399) (579,235) (1,184,512) Total consolidated assets $ 7,038,818 $ 7,833,159 $ 9,660,781
Schedule of Reconciliation of Assets from Segment to Consolidated	A reconciliation of reportable segment operating revenues and assets to consolidated operating revenues and assets is as follows: 2024 2023 2022 (In thousands) Operating revenues reconciliation: Total reportable segment operating revenues $ 1,827,402 $ 1,866,324 $ 1,806,456 Other revenue 195 119 86 Elimination of intersegment operating revenues (69,619) (63,091) (59,244) Total consolidated operating revenues $ 1,757,978 $ 1,803,352 $ 1,747,298 Asset reconciliation: Total reportable segment assets $ 6,892,959 $ 6,564,962 $ 6,061,151 Other assets 525,258 1,847,432 4,784,142 Elimination of intersegment receivables (379,399) (579,235) (1,184,512) Total consolidated assets $ 7,038,818 $ 7,833,159 $ 9,660,781

Employee Benefit Plans (Tables)

Employee Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2024
Retirement Benefits [Abstract]
Schedule of Amounts Recognized in Balance Sheet	Changes in benefit obligation and plan assets and amounts recognized in the Consolidated Balance Sheets at December 31 were as follows: Pension Benefits Other 2024 2023 2024 2023 Change in benefit obligation: (In thousands) Benefit obligation at beginning of year $ 275,586 $ 278,286 $ 39,590 $ 40,315 Service cost — — 505 534 Interest cost 12,799 13,521 1,837 1,956 Plan participants' contributions — — 412 479 Actuarial (gain) loss (11,040) 5,395 (3,420) (215) Benefits paid (21,995) (21,616) (3,249) (3,479) Benefit obligation at end of year 255,350 275,586 35,675 39,590 Change in net plan assets: Fair value of plan assets at beginning of year 248,558 242,031 79,234 76,640 Actual return on plan assets 1,152 20,576 2,297 5,518 Employer contribution 2,911 7,567 71 76 Plan participants' contributions — — 412 479 Benefits paid (21,995) (21,616) (3,249) (3,479) Fair value of net plan assets at end of year 230,626 248,558 78,765 79,234 Funded status - (under) over $ (24,724) $ (27,028) $ 43,090 $ 39,644 Amounts recognized in the Consolidated Balance Sheets at December 31: Noncurrent assets - other $ — $ — $ 43,090 $ 39,644 Noncurrent liabilities - other 24,724 27,028 — — Benefit obligation (liabilities) assets - net amount recognized $ (24,724) $ (27,028) $ 43,090 $ 39,644 Amounts recognized in accumulated other comprehensive loss: Actuarial loss (gain) $ 13,228 $ 32,273 $ (809) $ (3,515) Prior service credit — — (37) (115) Total $ 13,228 $ 32,273 $ (846) $ (3,630) Amounts recognized in regulatory assets or liabilities: Actuarial loss (gain) $ 139,962 $ 140,232 $ (1,478) $ (1,146) Prior service credit — — (1,303) (2,619) Total $ 139,962 $ 140,232 $ (2,781) $ (3,765)
Schedule of Accumulated and Projected Benefit Obligations	The pension plans all have accumulated benefit obligations in excess of plan assets. The projected benefit obligation, accumulated benefit obligation and fair value of plan assets for these plans at December 31 were as follows: 2024 2023 (In thousands) Projected benefit obligation $ 255,350 $ 275,586 Accumulated benefit obligation $ 255,350 $ 275,586 Fair value of plan assets $ 230,626 $ 248,558 The projected benefit obligation and accumulated benefit obligation for these plans at December 31 were as follows: 2024 2023 (In thousands) Projected benefit obligation $ 52,007 $ 57,033 Accumulated benefit obligation $ 52,007 $ 57,033
Schedule of Net Benefit Costs	The components of net periodic benefit cost (credit), other than the service cost component, are included in other income on the Consolidated Statements of Income. Prior service credit is amortized on a straight-line basis over the average remaining service period of active participants. These components related to the Company's pension and other postretirement benefit plans for the years ended December 31 were as follows: Pension Benefits Other 2024 2023 2022 2024 2023 2022 Components of net periodic benefit cost (credit): (In thousands) Service cost $ — $ — $ — $ 505 $ 534 $ 894 Interest cost 12,799 13,521 9,396 1,837 1,956 1,383 Expected return on assets (16,113) (17,194) (17,482) (5,315) (5,361) (5,277) Amortization of prior service credit — — — (1,318) (1,318) (1,318) Recognized net actuarial loss (gain) 4,149 3,093 5,826 (288) (504) (570) Net periodic benefit cost (credit), including amount capitalized 835 (580) (2,260) (4,579) (4,693) (4,888) Less amount capitalized — — — — 107 175 Net periodic benefit cost (credit) 835 (580) (2,260) (4,579) (4,800) (5,063) Other changes in plan assets and benefit obligations recognized in accumulated comprehensive loss: Net loss (gain) 401 187 2,369 71 (604) (4,141) Amortization of actuarial (loss) gain (359) (292) (1,310) 130 108 (281) Amortization of prior service credit — — — 45 78 125 Reclassification of postretirement liability adjustment from regulatory asset — — 5,343 — — (992) Total recognized in accumulated other comprehensive loss 42 (105) 6,402 246 (418) (5,289) Other changes in plan assets and benefit obligations recognized in regulatory assets or liabilities: Net loss (gain) 3,520 1,826 9,757 (472) (107) 11,920 Amortization of actuarial (loss) gain (3,790) (2,801) (5,373) 158 304 500 Amortization of prior service credit — — — 1,273 1,273 1,273 Reclassification of postretirement liability adjustment from regulatory asset — — (5,343) — — 992 Total recognized in regulatory assets or liabilities (270) (975) (959) 959 1,470 14,685 Total recognized in net periodic benefit credit, accumulated other comprehensive loss and regulatory assets or liabilities $ 607 $ (1,660) $ 3,183 $ (3,374) $ (3,748) $ 4,333 The components of net periodic benefit cost are included in other income on the Consolidated Statements of Income. These components related to the Company's nonqualified defined benefit plans for the years ended December 31 were as follows: 2024 2023 2022 (In thousands) Components of net periodic benefit cost: Interest cost $ 2,568 $ 2,740 $ 1,681 Recognized net actuarial loss 365 273 911 Net periodic benefit cost $ 2,933 $ 3,013 $ 2,592
Defined Benefit Plan, Assumptions	Weighted average assumptions used to determine benefit obligations at December 31 were as follows: Pension Benefits Other 2024 2023 2024 2023 Discount rate 5.41 % 4.84 % 5.43 % 4.85 % Expected return on plan assets 6.50 % 6.50 % 6.00 % 6.00 % Weighted average assumptions used to determine net periodic benefit cost (credit) for the years ended December 31 were as follows: Pension Benefits Other 2024 2023 2024 2023 Discount rate 4.84 % 5.06 % 4.85 % 5.07 % Expected return on plan assets 6.50 % 6.50 % 6.00 % 6.00 % Weighted average assumptions used at December 31 were as follows: 2024 2023 Benefit obligation discount rate 5.26 % 4.73 % Benefit obligation rate of compensation increase N/A N/A Net periodic benefit cost discount rate 4.73 % 4.97 % Net periodic benefit cost rate of compensation increase N/A N/A
Schedule of Health Care Cost Trend Rates	Health care rate assumptions for the Company's other postretirement benefit plans as of December 31 were as follows: 2024 2023 Health care trend rate assumed for next year (pre-65/post-65) 8.5%/6.25% 7.5%/6.5% Health care cost trend rate - ultimate 4.5 % 4.5 % Year in which ultimate trend rate achieved (pre-65/post-65) 2035/2034 2034/2033
Schedule of Expected Benefit Payments	The following benefit payments, which reflect future service, as appropriate, and expected Medicare Part D subsidies at December 31, 2024, are as follows: Years Pension Other Expected (In thousands) 2025 $ 22,280 $ 3,333 $ 48 2026 $ 22,070 $ 3,235 $ 43 2027 $ 21,870 $ 3,153 $ 37 2028 $ 21,500 $ 3,064 $ 32 2029 $ 21,170 $ 2,941 $ 27 2030-2034 $ 98,020 $ 13,659 $ 85 The amount of future benefit payments for the unfunded, nonqualified defined benefit plans at December 31, 2024, are expected to aggregate as follows: 2025 2026 2027 2028 2029 2030-2034 (In thousands) Nonqualified benefits $ 5,700 $ 5,610 $ 5,830 $ 5,560 $ 5,190 $ 20,920
Schedule of Allocation of Plan Assets	The fair value of the Company's pension plans' assets (excluding cash) by class were as follows: Fair Value Measurements at December 31, 2024, Using Quoted Prices Significant Significant Balance at December 31, 2024 (In thousands) Assets: Cash equivalents $ — $ 4,512 $ — $ 4,512 Equity securities: U.S. companies (2) — — (2) Collective and mutual funds (a) 72,777 93,606 — 166,383 U.S. Government securities 33,616 25,857 — 59,473 Investments measured at net asset value (b) — — — 260 Total assets measured at fair value $ 106,391 $ 123,975 $ — $ 230,626 (a) Collective and mutual funds invest approximately 39 percent in corporate bonds, 19 percent in U.S. Government securities, 17 percent in other investments, 15 percent in common stock of international companies, 9 percent in common stock of large-cap and mid-cap U.S. companies, and 1 percent cash and cash equivalents. (b) In accordance with ASC 820 - Fair Value Measurements, certain investments that were measured at net asset value per share (or its equivalent) have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the line items presented in the Consolidated Balance Sheets. Fair Value Measurements at December 31, 2023, Using Quoted Prices Significant Significant Balance at December 31, 2023 (In thousands) Assets: Cash equivalents $ — $ 7,197 $ — $ 7,197 Equity securities: U.S. companies (2) — — (2) Collective and mutual funds (a) 84,761 88,219 — 172,980 U.S. Government securities 30,162 33,141 — 63,303 Investments measured at net asset value (b) — — — 5,080 Total assets measured at fair value $ 114,921 $ 128,557 $ — $ 248,558 (a) Collective and mutual funds invest approximately 51 percent in corporate bonds, 15 percent in common stock of international companies, 11 percent in common stock of large-cap and mid-cap U.S. companies, 7 percent cash and cash equivalents, 7 percent in U.S. Government securities and 9 percent in other investments. (b) In accordance with ASC 820 - Fair Value Measurements, certain investments that were measured at net asset value per share (or its equivalent) have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the line items presented in the Consolidated Balance Sheets. The fair value of the Company's other postretirement benefit plans' assets (excluding cash) by asset class were as follows: Fair Value Measurements Quoted Prices Significant Significant Balance at December 31, 2024 (In thousands) Assets: Cash equivalents $ — $ 4,373 $ — $ 4,373 Equity securities: U.S. companies 2,880 — — 2,880 Insurance contract (a) — 71,512 — 71,512 Total assets measured at fair value $ 2,880 $ 75,885 $ — $ 78,765 (a) The insurance contract invests approximately 41 percent in corporate bonds, 28 percent in U.S. Government securities, 19 percent in common stock of large-cap U.S. companies, 6 percent in common stock of small-cap U.S. companies and 6 percent in other investments. Fair Value Measurements Quoted Prices Significant Significant Balance at December 31, 2023 (In thousands) Assets: Cash equivalents $ — $ 4,562 $ — $ 4,562 Equity securities: U.S. companies 2,369 — — 2,369 Insurance contract (a) — 72,303 — 72,303 Total assets measured at fair value $ 2,369 $ 76,865 $ — $ 79,234 (a) The insurance contract invests approximately 60 percent in corporate bonds, 16 percent in common stock of large-cap U.S. companies, 15 percent in U.S. Government securities, 5 percent in common stock of small-cap U.S. companies and 4 percent in other investments. The amount of investments that the Company anticipates using to satisfy obligations under these plans at December 31 was as follows: 2024 2023 (In thousands) Investments Insurance contracts* $ 59,282 $ 62,936 Life insurance** 30,834 31,303 Other 12,879 6,409 Total investments $ 102,995 $ 100,648 * For more information on the insurance contracts, see Note 9. ** Investments of life insurance are carried on plan participants (payable upon the employee's death).
Schedule of Multiemployer Plans	EIN/Pension Plan Number Pension Protection Act Zone Status FIP/RP Status Pending/Implemented Contributions Surcharge Imposed Expiration Date Pension Fund 2024 2023 2024 2023 2022 (In thousands) Idaho Plumbers and Pipefitters Pension Plan 826010346-001 Green as of 5/31/2024 Green as of 5/31/2023 No $ 1,434 $ 1,690 $ 1,613 No 3/31/2027 Total contributions $ 1,434 $ 1,690 $ 1,613 The Company was listed in the plans' Forms 5500 as providing more than 5 percent of the total contributions for the following plans and plan years: Pension Fund Year Contributions to Plan Exceeded More Than 5 Percent Idaho Plumbers and Pipefitters Pension Plan 2023 and 2022

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2024
Commitments and Contingencies Disclosure [Abstract]
Schedule of Long-Term Purchase Commitment	The commitment terms vary in length, up to 35 years. The commitments under these contracts as of December 31, 2024, were: 2025 2026 2027 2028 2029 Thereafter (In thousands) Purchase commitments $ 658,012 $ 310,894 $ 210,152 $ 177,613 $ 147,081 $ 1,221,125
Schedule of Lease Costs	The following tables provide information on the Company's operating leases at and for the years ended December 31: 2024 2023 2022 (In thousands) Lease costs: Short-term lease cost $ 1,549 $ 1,646 $ 1,373 Operating lease cost 3,069 2,871 2,497 Variable lease cost 819 676 413 $ 5,437 $ 5,193 $ 4,283 2024 2023 2022 (Dollars in thousands) Weighted average remaining lease term 12.65 years 15.35 years 15.15 years Weighted average discount rate 6.08 % 4.88 % 4.65 % Cash paid for amounts included in the measurement of lease liabilities $ 3,063 $ 2,868 $ 2,500
Schedule of Operating Lease Liabilities Undiscounted Cash Flows Maturity	The reconciliation of future undiscounted cash flows to operating lease liabilities presented on the Consolidated Balance Sheet at December 31, 2024, was as follows: (In thousands) 2025 $ 3,034 2026 2,648 2027 2,011 2028 1,570 2029 1,492 Thereafter 20,808 Total 31,563 Less discount 10,654 Total operating lease liabilities $ 20,909

Jointly Owned Facilities (Table

Jointly Owned Facilities (Tables)	12 Months Ended
	Dec. 31, 2024
Regulated Operations [Abstract]
Schedule of Jointly Owned Utility Plants	At December 31, the Company's share of the cost of utility plant in service, construction work in progress and related accumulated depreciation for the jointly owned facilities was as follows: Ownership Percentage 2024 2023 (In thousands) Big Stone Station: 22.7 % Utility plant in service $ 155,302 $ 159,437 CWIP 318 197 Less accumulated depreciation 55,327 52,264 $ 100,293 $ 107,370 BSSE: 50.0 % Utility plant in service $ 111,043 $ 107,260 CWIP — — Less accumulated depreciation 10,359 8,111 $ 100,684 $ 99,149 Coyote Station: 25.0 % Utility plant in service $ 160,343 $ 160,208 CWIP 755 159 Less accumulated depreciation 115,133 113,187 $ 45,965 $ 47,180 JETx: 50.0 % Utility plant in service $ — $ — CWIP 6,112 1,372 Less accumulated depreciation — — $ 6,112 $ 1,372 Wygen III: 25.0 % Utility plant in service $ 67,851 $ 66,852 CWIP 97 127 Less accumulated depreciation 15,340 13,728 $ 52,608 $ 53,251

Basis of Presentation (Details)

Basis of Presentation (Details) $ in Thousands, shares in Millions			12 Months Ended
	Oct. 31, 2024	May 31, 2023 shares	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Electric fuel and purchased power			$ 141,148	$ 134,779	$ 119,405
Operation and maintenance			$ (414,491)	(407,081)	(379,951)
Revision of Prior Period, Error Correction, Adjustment
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Electric fuel and purchased power				26,900	27,400
Operation and maintenance				$ 26,900	$ 27,400
Discontinued Operations, Disposed of by Means Other than Sale, Spinoff | Knife River Corporation
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Pro rata distribution of shares, percentage		0.90
Stock split, conversion ratio		0.25
Retained ownership percentage		0.10
Number of retained shares (in shares) | shares		5.7
Discontinued Operations, Disposed of by Means Other than Sale, Spinoff | Everus
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Stock split, conversion ratio	0.25

Significant Accounting Polici_4

Significant Accounting Policies - Cash, Cash Equivalents And Restricted Cash (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Accounting Policies [Abstract]
Restricted cash	$ 16.7	$ 13.2

Significant Accounting Polici_5

Significant Accounting Policies - Receivables And Allowance For Expected Credit Losses (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Accounting Policies [Abstract]
Accounts receivable, 90 days or more past due	$ 3.6	$ 3.7
Accrued unbilled revenue	$ 143.2	$ 132

Significant Accounting Polici_6

Significant Accounting Policies - Schedule of Expected Credit Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Current expected credit loss provision	$ 6,558	$ 7,422	$ 5,409
Trade Accounts Receivable
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Accounts receivable, allowance for credit loss, beginning balance	1,603	1,992
Current expected credit loss provision	6,558	7,422
Less write-offs charged against the allowance	7,927	9,351
Credit loss recoveries collected	1,605	1,540
Accounts receivable, allowance for credit loss, ending balance	1,839	1,603	1,992
Trade Accounts Receivable | Electric
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Accounts receivable, allowance for credit loss, beginning balance	414	375
Current expected credit loss provision	1,891	1,645
Less write-offs charged against the allowance	2,218	1,994
Credit loss recoveries collected	386	388
Accounts receivable, allowance for credit loss, ending balance	473	414	375
Trade Accounts Receivable | Natural gas distribution
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Accounts receivable, allowance for credit loss, beginning balance	1,189	1,615
Current expected credit loss provision	4,667	5,777
Less write-offs charged against the allowance	5,709	7,355
Credit loss recoveries collected	1,219	1,152
Accounts receivable, allowance for credit loss, ending balance	1,366	1,189	1,615
Trade Accounts Receivable | Pipeline
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Accounts receivable, allowance for credit loss, beginning balance	0	2
Current expected credit loss provision	0	0
Less write-offs charged against the allowance	0	2
Credit loss recoveries collected	0	0
Accounts receivable, allowance for credit loss, ending balance	$ 0	$ 0	$ 2

Significant Accounting Polici_7

Significant Accounting Policies - Inventories And Natural Gas In Storage (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Accounting Policies [Abstract]
Natural gas in storage (current)	$ 40,073	$ 39,377
Fuel stock	4,867	5,307
Total	44,940	44,684
Natural gas in storage (noncurrent)	$ 48,500	$ 48,500

Significant Accounting Polici_8

Significant Accounting Policies - Schedule of Property, Plant and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Accounting Policies [Abstract]
AFUDC - borrowed	$ 10,964	$ 10,035	$ 2,236
AFUDC - equity	$ 2,251	$ 1,894	$ 2,165

Significant Accounting Polici_9

Significant Accounting Policies - Impairment of Long-Lived Assets, Excluding Goodwill (Details) - USD ($)	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Accounting Policies [Abstract]
Impairment losses	$ 0	$ 0	$ 0

Significant Accounting Polic_10

Significant Accounting Policies - Goodwill (Details) - USD ($)	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Accounting Policies [Abstract]
Goodwill, impairment loss	$ 0	$ 0	$ 0

Significant Accounting Polic_11

Significant Accounting Policies - Earnings Per Share (Details) - $ / shares		12 Months Ended
	May 31, 2023	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average common shares outstanding - basic (in shares)		203,867,000	203,640,000	203,358,000
Effect of dilutive performance share awards (in shares)		786,000	298,000	104,000
Weighted average common shares outstanding - diluted (in shares)		204,653,000	203,938,000	203,462,000
Earnings per share - basic:
Income from continuing operations (in usd per share)		$ 0.89	$ 1.62	$ 0.58
Discontinued operations, net of tax (in usd per share)		0.49	0.42	1.23
Earnings per share - basic (in usd per share)		1.38	2.04	1.81
Earnings per share - diluted:
Income from continuing operations (in usd per share)		0.88	1.62	0.58
Discontinued operations, net of tax (in usd per share)		0.49	0.41	1.23
Earnings per share - diluted (in usd per share)		$ 1.37	$ 2.03	$ 1.81
Shares excluded from the calculation of diluted earnings per share (in shares)		0	0	14,000
Dividends declared per common share (in usd per share)		$ 0.5100	$ 0.6950	$ 0.8750
Discontinued Operations, Disposed of by Means Other than Sale, Spinoff | Knife River Corporation
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Treasury stock, retired (in shares)	538,921

Significant Accounting Polic_12

Significant Accounting Policies - Income Taxes (Details)	12 Months Ended
	Dec. 31, 2024
Accounting Policies [Abstract]
Threshold of likelihood of tax positions being realized upon ultimate settlement with a taxing authority	0.50

Discontinued Operations - Narra

Discontinued Operations - Narrative (Details) $ in Thousands				1 Months Ended	12 Months Ended
	Oct. 31, 2024	May 31, 2023 shares	Apr. 25, 2023 USD ($)	Nov. 30, 2023 USD ($)	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Realized gain on tax-free exchange of the retained shares in Knife River					$ 0	$ 186,556	$ 0
Long-term debt					2,292,610	2,166,223
Repayments of long-term debt					$ 182,135	$ 568,883	$ 38,764
Restructuring Charges, Statement of Income or Comprehensive Income [Extensible Enumeration]					Income from discontinued operations, net of tax	Income from discontinued operations, net of tax	Income from discontinued operations, net of tax
Knife River Corporation
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Repayments of long-term debt			$ 825,000
Knife River Corporation | Revolving Credit Facility
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Line of credit facility, maximum borrowing capacity			350,000
Knife River Corporation | Term Loan Agreement
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Debt instrument, face amount			275,000
Senior Notes | Knife River Corporation
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Long-term debt			$ 425,000
Discontinued Operations, Disposed of by Means Other than Sale, Spinoff | Knife River Corporation
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Pro rata distribution of shares, percentage		0.90
Stock split, conversion ratio		0.25
Retained ownership percentage		0.10
Number of retained shares (in shares) | shares		5,700,000
Realized gain on tax-free exchange of the retained shares in Knife River				$ 186,600
Separation of Knife River (in shares) | shares		538,921
Separation related costs					$ 41,700	$ 58,600	$ 11,500
Discontinued Operations, Disposed of by Means Other than Sale, Spinoff | Knife River Corporation | Cash Received, TSA
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Discontinued operation, amount of continuing cash flows after disposal					1,500	2,900
Discontinued Operations, Disposed of by Means Other than Sale, Spinoff | Knife River Corporation | Cash Paid, TSA
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Discontinued operation, amount of continuing cash flows after disposal					$ 159	$ 823
Discontinued Operations, Disposed of by Means Other than Sale, Spinoff | Everus
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Stock split, conversion ratio	0.25
Discontinued operation, period of continuing involvement					18 months
Discontinued Operations, Disposed of by Means Other than Sale, Spinoff | Everus | Maximum
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Discontinued operation, period of continuing involvement					2 years
Discontinued Operations, Disposed of by Means Other than Sale, Spinoff | Everus | Cash Received, TSA
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Discontinued operation, amount of continuing cash flows after disposal					$ 727
Discontinued Operations, Disposed of by Means Other than Sale, Spinoff | Everus | Cash Paid, TSA
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Discontinued operation, amount of continuing cash flows after disposal					$ 47

Discontinued Operations - Sched

Discontinued Operations - Schedule of Assets and Liabilities of Discontinued Operations (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents		$ 16,500	$ 9,700
Noncurrent assets:
Noncurrent assets of discontinued operations	$ 0	347,865
Current liabilities:
Total current liabilities of discontinued operations	0	443,280
Noncurrent liabilities:
Total noncurrent liabilities of discontinued operations	$ 0	179,650
Everus Corporation | Discontinued Operations, Disposed of by Means Other than Sale, Spinoff
Current assets:
Cash and cash equivalents		16,501
Receivables, net		692,629
Inventories		42,709
Prepayments and other current assets		17,651
Total current assets of discontinued operations		769,490
Noncurrent assets:
Net property, plant and equipment		116,018
Goodwill		143,224
Other intangible assets, net		2,004
Investments		11,760
Operating lease right-of-use assets		53,232
Other		21,627
Noncurrent assets of discontinued operations		347,865
Total assets of discontinued operations		1,117,355
Current liabilities:
Accounts payable		315,240
Taxes payable		8,557
Accrued compensation		44,721
Operating lease liabilities due within one year		21,143
Other accrued liabilities		53,619
Total current liabilities of discontinued operations		443,280
Noncurrent liabilities:
Long-term debt		132,000
Deferred income taxes		6,212
Operating lease liabilities		32,504
Other		8,934
Total noncurrent liabilities of discontinued operations		179,650
Total liabilities of discontinued operations		$ 622,930

Discontinued Operations - Sch_2

Discontinued Operations - Schedule of Income and Expense Constituting Pretax Income From Discontinued Operations (Details) - Knife River Corporation - Discontinued Operations, Disposed of by Means Other than Sale, Spinoff - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Operating revenues	$ 2,377,332	$ 3,589,251	$ 5,226,766
Operating expenses	2,241,162	3,422,393	4,853,408
Operating (loss) income	136,170	166,858	373,358
Other income (expense)	12,446	10,599	4,119
Interest expense	7,118	47,229	38,590
Income from discontinued operations before income taxes	141,498	130,228	338,887
Income taxes	41,463	45,638	88,650
Discontinued operations, net of tax	$ 100,035	$ 84,590	$ 250,237

Revenue from Contracts with C_3

Revenue from Contracts with Customers - Schedule of Disaggregation of Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 1,752,995	$ 1,805,807	$ 1,754,158
Other revenues	4,983	(2,455)	(6,860)
Total external operating revenues	1,757,978	1,803,352	1,747,298
Operating Segments
Disaggregation of Revenue [Line Items]
Total external operating revenues	1,827,402	1,866,324	1,806,456
Intersegment eliminations
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	(69,619)	(63,091)	(59,244)
Total external operating revenues	(69,619)	(63,091)	(59,244)
Natural gas transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	235,268	197,762	178,176
Natural gas storage
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	23,690	18,254	14,583
Other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	113,325	83,642	70,761
Residential utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	786,103	860,874	856,825
Commercial utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	570,847	612,828	599,984
Industrial utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	85,471	88,268	85,476
Other utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	7,910	7,270	7,597
Electric | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	421,823	411,298	381,729
Other revenues	(7,417)	(10,261)	(4,714)
Total external operating revenues	414,406	401,037	377,015
Electric | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	(72)	(138)	(58)
Total external operating revenues	(72)	(138)	(58)
Electric | Natural gas transportation | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Electric | Natural gas storage | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Electric | Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	59,288	54,508	45,608
Electric | Residential utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	140,054	136,274	138,634
Electric | Commercial utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	171,760	170,321	146,182
Electric | Industrial utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	42,883	43,063	43,766
Electric | Other utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	7,910	7,270	7,597
Natural gas distribution | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	1,188,942	1,279,617	1,275,990
Other revenues	12,033	7,619	(2,402)
Total external operating revenues	1,200,975	1,287,236	1,273,588
Natural gas distribution | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	(130)	(301)	(216)
Total external operating revenues	(130)	(301)	(216)
Natural gas distribution | Natural gas transportation | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	60,645	52,465	48,886
Natural gas distribution | Natural gas storage | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Natural gas distribution | Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	40,703	15,141	13,617
Natural gas distribution | Residential utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	646,049	724,600	718,191
Natural gas distribution | Commercial utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	399,087	442,507	453,802
Natural gas distribution | Industrial utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	42,588	45,205	41,710
Natural gas distribution | Other utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Pipeline | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	142,230	114,892	96,439
Other revenues	367	187	256
Total external operating revenues	142,597	115,079	96,695
Pipeline | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	(69,222)	(62,533)	(58,884)
Total external operating revenues	(69,222)	(62,533)	(58,884)
Pipeline | Natural gas transportation | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	174,623	145,297	129,290
Pipeline | Natural gas storage | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	23,690	18,254	14,583
Pipeline | Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	13,139	13,874	11,450
Pipeline | Residential utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Pipeline | Commercial utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Pipeline | Industrial utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Pipeline | Other utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Other revenues	0	0	0
Total external operating revenues	0	0	0
Other | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	(195)	(119)	(86)
Total external operating revenues	(195)	(119)	(86)
Other | Natural gas transportation | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Other | Natural gas storage | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Other | Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	195	119	86
Other | Residential utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Other | Commercial utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Other | Industrial utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Other | Other utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 0	$ 0	$ 0

Revenue from Contracts with C_4

Revenue from Contracts with Customers - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2024 USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation, amount	$ 606.5
Firm Transportation Contract
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue from contract with customer, term of contract	5 years
Firm Storage Contract
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue from contract with customer, term of contract	1 year
Remaining performance obligation, expected timing of satisfaction, start date: 2025-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation, amount	$ 82.1
Revenue, remaining performance obligation, expected timing of satisfaction, period	12 months
Remaining performance obligation, expected timing of satisfaction, start date: 2026-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation, amount	$ 81.5
Revenue, remaining performance obligation, expected timing of satisfaction, period	12 months
Remaining performance obligation, expected timing of satisfaction, start date: 2027-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation, amount	$ 442.9
Revenue, remaining performance obligation, expected timing of satisfaction, period

Property, Plant and Equipment_2

Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Property, plant and equipment [Line Items]
Property, plant and equipment	$ 7,554,063	$ 7,081,267	$ 6,629,518
Less accumulated depreciation and amortization	2,209,771	2,076,375	$ 1,963,260
Net property, plant and equipment	5,344,292	5,004,892
Electric | Electric Equipment
Property, plant and equipment [Line Items]
Property, plant and equipment	$ 1,014,906	939,474
Weighted Average Depreciable Life in Years	49 years
Electric | Electric Distribution
Property, plant and equipment [Line Items]
Property, plant and equipment	$ 546,121	521,215
Weighted Average Depreciable Life in Years	47 years
Electric | Electric Transmission
Property, plant and equipment [Line Items]
Property, plant and equipment	$ 662,466	639,999
Weighted Average Depreciable Life in Years	65 years
Electric | CWIP
Property, plant and equipment [Line Items]
Property, plant and equipment	$ 81,316	115,103
Electric | Other
Property, plant and equipment [Line Items]
Property, plant and equipment	$ 176,007	153,248
Weighted Average Depreciable Life in Years	15 years
Natural gas distribution | CWIP
Property, plant and equipment [Line Items]
Property, plant and equipment	$ 74,207	70,373
Natural gas distribution | Other
Property, plant and equipment [Line Items]
Property, plant and equipment	$ 282,007	246,991
Weighted Average Depreciable Life in Years	15 years
Natural gas distribution | Gas Distribution
Property, plant and equipment [Line Items]
Property, plant and equipment	$ 2,955,435	2,771,540
Weighted Average Depreciable Life in Years	53 years
Natural gas distribution | Gas Transmission
Property, plant and equipment [Line Items]
Property, plant and equipment	$ 146,710	115,057
Weighted Average Depreciable Life in Years	56 years
Natural gas distribution | Storage
Property, plant and equipment [Line Items]
Property, plant and equipment	$ 43,700	42,654
Weighted Average Depreciable Life in Years	37 years
Natural gas distribution | General
Property, plant and equipment [Line Items]
Property, plant and equipment	$ 229,034	215,572
Weighted Average Depreciable Life in Years	13 years
Pipeline | CWIP
Property, plant and equipment [Line Items]
Property, plant and equipment	$ 29,629	57,038
Pipeline | Other
Property, plant and equipment [Line Items]
Property, plant and equipment	$ 73,749	68,194
Weighted Average Depreciable Life in Years	17 years
Pipeline | Gas Transmission
Property, plant and equipment [Line Items]
Property, plant and equipment	$ 1,173,259	1,035,995
Weighted Average Depreciable Life in Years	46 years
Pipeline | Storage
Property, plant and equipment [Line Items]
Property, plant and equipment	$ 61,369	57,160
Weighted Average Depreciable Life in Years	53 years
Other | Land and other
Property, plant and equipment [Line Items]
Property, plant and equipment	$ 4,148	$ 31,654
Weighted Average Depreciable Life in Years	7 years

Regulatory Assets and Liabili_3

Regulatory Assets and Liabilities - Schedule of Unamortized Regulatory Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Regulatory Asset [Abstract]
Current regulatory assets	$ 215,436	$ 172,492
Regulatory assets	322,350	447,099
Total regulatory assets	537,786	619,591
Regulatory Liability [Abstract]
Regulatory liabilities due within one year	137,167	70,761
Regulatory liabilities	459,170	521,050
Total regulatory liabilities	596,337	591,811
Net regulatory position	$ (58,551)	27,780
Environmental compliance programs
Regulatory Liability [Abstract]
Estimated Recovery or Refund Period	1 year
Regulatory liabilities due within one year	$ 72,387	0
Regulatory liabilities	$ 0	61,941
Natural gas costs refundable through rate adjustments
Regulatory Liability [Abstract]
Estimated Recovery or Refund Period	1 year
Regulatory liabilities due within one year	$ 45,427	43,161
Margin sharing
Regulatory Liability [Abstract]
Estimated Recovery or Refund Period	1 year
Regulatory liabilities due within one year	$ 4,156	5,243
Provision for rate refund
Regulatory Liability [Abstract]
Estimated Recovery or Refund Period	1 year
Regulatory liabilities due within one year	$ 3,677	6,866
Taxes refundable to customers
Regulatory Liability [Abstract]
Estimated Recovery or Refund Period	1 year
Regulatory liabilities due within one year	$ 2,163	2,149
Regulatory liabilities	$ 185,402	193,578
Conservation programs
Regulatory Liability [Abstract]
Estimated Recovery or Refund Period	1 year
Regulatory liabilities due within one year	$ 2,082	2,130
Cost recovery mechanisms
Regulatory Liability [Abstract]
Estimated Recovery or Refund Period	17 years
Regulatory liabilities due within one year	$ 1,720	6,284
Regulatory liabilities	$ 30,354	21,791
Cost recovery mechanisms | Maximum
Regulatory Liability [Abstract]
Estimated Recovery or Refund Period	1 year
Other
Regulatory Liability [Abstract]
Estimated Recovery or Refund Period	13 years
Regulatory liabilities due within one year	$ 5,555	4,928
Regulatory liabilities	$ 2,161	1,809
Other | Maximum
Regulatory Liability [Abstract]
Estimated Recovery or Refund Period	1 year
Plant removal and decommissioning costs
Regulatory Liability [Abstract]
Regulatory liabilities	$ 217,603	220,147
Accumulated deferred investment tax credit
Regulatory Liability [Abstract]
Regulatory liabilities	18,788	15,740
Pension and postretirement benefits
Regulatory Liability [Abstract]
Regulatory liabilities	4,862	6,044
Natural gas costs recoverable through rate adjustments
Regulatory Asset [Abstract]
Current regulatory assets	91,091	98,844
Regulatory assets	$ 0	55,493
Natural gas costs recoverable through rate adjustments | Minimum
Regulatory Asset [Abstract]
Estimated Recovery or Refund Period	1 year
Natural gas costs recoverable through rate adjustments | Maximum
Regulatory Asset [Abstract]
Estimated Recovery or Refund Period	2 years
Environmental compliance programs
Regulatory Asset [Abstract]
Current regulatory assets	$ 76,964	5,525
Regulatory assets	$ 0	66,806
Environmental compliance programs | Minimum
Regulatory Asset [Abstract]
Estimated Recovery or Refund Period	1 year
Conservation programs
Regulatory Asset [Abstract]
Estimated Recovery or Refund Period	1 year
Current regulatory assets	$ 19,123	14,425
Electric fuel and purchased power deferral
Regulatory Asset [Abstract]
Current regulatory assets	9,662	33,918
Regulatory assets	$ 4,349	0
Electric fuel and purchased power deferral | Minimum
Regulatory Asset [Abstract]
Estimated Recovery or Refund Period	1 year
Electric fuel and purchased power deferral | Maximum
Regulatory Asset [Abstract]
Estimated Recovery or Refund Period	2 years
Decoupling mechanisms
Regulatory Asset [Abstract]
Estimated Recovery or Refund Period	1 year
Current regulatory assets	$ 6,767	0
Cost recovery mechanisms
Regulatory Asset [Abstract]
Current regulatory assets	5,114	9,153
Regulatory assets	$ 76,542	85,944
Cost recovery mechanisms | Minimum
Regulatory Asset [Abstract]
Estimated Recovery or Refund Period	1 year
Cost recovery mechanisms | Maximum
Regulatory Asset [Abstract]
Estimated Recovery or Refund Period	24 years
Other
Regulatory Asset [Abstract]
Estimated Recovery or Refund Period	14 years
Current regulatory assets	$ 6,715	10,627
Regulatory assets	$ 5,990	6,614
Other | Minimum
Regulatory Asset [Abstract]
Estimated Recovery or Refund Period	1 year
Pension and postretirement benefits
Regulatory Asset [Abstract]
Regulatory assets	$ 142,064	142,511
Plant costs/asset retirement obligations
Regulatory Asset [Abstract]
Regulatory assets	47,042	46,009
Manufactured gas plant site remediation
Regulatory Asset [Abstract]
Regulatory assets	27,964	26,127
Taxes refundable to customers
Regulatory Asset [Abstract]
Regulatory assets	12,221	12,249
Covid-19 deferred costs
Regulatory Asset [Abstract]
Regulatory assets	$ 4,167	2,746
Long-term debt refinancing costs
Regulatory Asset [Abstract]
Estimated Recovery or Refund Period	36 years
Regulatory assets	$ 2,011	$ 2,600

Regulatory Assets and Liabili_4

Regulatory Assets and Liabilities - Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory assets not earning a rate of return	$ 181.2	$ 194.3

Goodwill (Details)

Goodwill (Details) - USD ($)	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Goodwill [Line Items]
Goodwill	$ 345,736,000	$ 345,736,000
Goodwill, impairment loss	0	0	$ 0
Natural gas distribution
Goodwill [Line Items]
Goodwill	$ 345,700,000	$ 345,700,000

Fair Value Measurements - Narra

Fair Value Measurements - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Fair Value Disclosures [Abstract]
Investments used to satisfy nonqualified benefit plans obligations		$ 62.9	$ 59.3	$ 62.9
Unrealized gains (losses) on investments, net of insurance proceeds			$ 5.9	$ 7.4	$ (11.2)
Investment withdrawal, reduction in cost basis	$ 9	$ 20

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Available-for-Sale Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Debt Securities, Available-for-sale [Abstract]
Cost	$ 11,878	$ 11,755
Gross Unrealized Gains	84	45
Gross Unrealized Losses	384	478
Fair Value	11,578	11,322
Mortgage-backed securities
Debt Securities, Available-for-sale [Abstract]
Cost	7,933	8,234
Gross Unrealized Gains	4	17
Gross Unrealized Losses	383	470
Fair Value	7,554	7,781
U.S. Treasury securities
Debt Securities, Available-for-sale [Abstract]
Cost	3,945	3,521
Gross Unrealized Gains	80	28
Gross Unrealized Losses	1	8
Fair Value	$ 4,024	$ 3,541

Fair Value Measurements - Sch_2

Fair Value Measurements - Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Concentration Risks, Percentage [Abstract]
Percentage in fixed-income investments	58%	60%
Percentage investment in common stock of large-cap companies	17%	15%
Percentage investment in target date investments	8%	8%
Percentage investment in common stock of mid-cap companies	8%	7%
Percentage investment in common stock of small-cap companies	4%	5%
Percentage investment in cash and cash equivalents	4%	3%
Percentage investment in high-yield investments		1%
Percentage investment in international investments	1%	1%
Fair Value, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure	$ 83,739	$ 80,667
Fair Value, Recurring | Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure	12,879	6,409
Fair Value, Recurring | Insurance contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure	59,282	62,936
Fair Value, Recurring | Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure	7,554	7,781
Fair Value, Recurring | U.S. Treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure	4,024	3,541
Quoted Prices in Active Markets for Identical Assets  (Level 1) | Fair Value, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure	0	0
Quoted Prices in Active Markets for Identical Assets  (Level 1) | Fair Value, Recurring | Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure	0	0
Quoted Prices in Active Markets for Identical Assets  (Level 1) | Fair Value, Recurring | Insurance contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure	0	0
Quoted Prices in Active Markets for Identical Assets  (Level 1) | Fair Value, Recurring | Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure	0	0
Quoted Prices in Active Markets for Identical Assets  (Level 1) | Fair Value, Recurring | U.S. Treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure	0	0
Significant Other Observable Inputs  (Level 2) | Fair Value, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure	83,739	80,667
Significant Other Observable Inputs  (Level 2) | Fair Value, Recurring | Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure	12,879	6,409
Significant Other Observable Inputs  (Level 2) | Fair Value, Recurring | Insurance contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure	59,282	62,936
Significant Other Observable Inputs  (Level 2) | Fair Value, Recurring | Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure	7,554	7,781
Significant Other Observable Inputs  (Level 2) | Fair Value, Recurring | U.S. Treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure	4,024	3,541
Significant Unobservable Inputs  (Level 3) | Fair Value, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure	0	0
Significant Unobservable Inputs  (Level 3) | Fair Value, Recurring | Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure	0	0
Significant Unobservable Inputs  (Level 3) | Fair Value, Recurring | Insurance contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure	0	0
Significant Unobservable Inputs  (Level 3) | Fair Value, Recurring | Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure	0	0
Significant Unobservable Inputs  (Level 3) | Fair Value, Recurring | U.S. Treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure	$ 0	$ 0

Fair Value Measurements - Sch_3

Fair Value Measurements - Schedule of Fair Value, by Balance Sheet Grouping (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	$ 2,292,610	$ 2,166,223
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	2,292,610	2,166,223
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	$ 1,963,396	$ 1,914,039

Debt - Schedule of Credit Facil

Debt - Schedule of Credit Facilities (Details) - USD ($)	Dec. 31, 2024	Dec. 31, 2023
Line of Credit Facility [Line Items]
Letters of credit at end of period	$ 0
Credit Agreement Expiring October 2028 | Revolving Credit Facility | Montana-Dakota Utilities Co.
Line of Credit Facility [Line Items]
Facility Limit	200,000,000
Amount outstanding, end of period	81,400,000	$ 144,200,000
Letters of credit at end of period	0	0
Option to increase borrowings, maximum amount	250,000,000
Credit Agreement Expiring June 2029 | Revolving Credit Facility | Cascade Natural Gas Corporation
Line of Credit Facility [Line Items]
Facility Limit	175,000,000
Amount outstanding, end of period	64,600,000	15,400,000
Letters of credit at end of period	2,200,000
Option to increase borrowings, maximum amount	225,000,000
Credit Agreement Expiring June 2029 | Revolving Credit Facility | Intermountain Gas Company
Line of Credit Facility [Line Items]
Facility Limit	175,000,000
Amount outstanding, end of period	105,100,000	30,700,000
Letters of credit at end of period	0
Credit Agreement Expiring May 2028 | Revolving Credit Facility | MDU Resources Group, Inc.
Line of Credit Facility [Line Items]
Facility Limit	200,000,000
Amount outstanding, end of period	0	$ 0
Letters of credit at end of period	12,100,000
Option to increase borrowings, maximum amount	$ 250,000,000

Debt - Short-Term Debt (Details

Debt - Short-Term Debt (Details) - USD ($)			1 Months Ended			12 Months Ended
	Jan. 19, 2024	Dec. 05, 2023	May 31, 2023	Apr. 30, 2023	Mar. 31, 2023	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Jan. 20, 2023
Short-term Debt [Line Items]
Short-term borrowings						$ 0	$ 95,000,000
Repayment of short-term borrowings						$ 95,000,000	433,901,000	$ 0
MDU Resources Group, Inc. | Revolving Credit Facility
Short-term Debt [Line Items]
Short-term borrowings			$ 150,000,000				$ 0
Term Loan Agreement | Cascade Natural Gas
Short-term Debt [Line Items]
Short-term borrowings									$ 150,000,000
Repayment of short-term borrowings	$ 50,000,000	$ 100,000,000
Term Loan Agreement | Intermountain Gas Company
Short-term Debt [Line Items]
Short-term borrowings									$ 125,000,000
Repayment of short-term borrowings	$ 45,000,000		$ 30,000,000	$ 30,000,000	$ 20,000,000

Debt - Schedule of Long-Term De

Debt - Schedule of Long-Term Debt Outstanding (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Long-term debt outstanding [Line Items]
Less unamortized debt issuance costs	$ 6,436	$ 6,357
Total long-term debt	2,292,610	2,166,223
Less current maturities	161,700	61,319
Net long-term debt	$ 2,130,910	2,104,904
Senior Notes
Long-term debt outstanding [Line Items]
Weighted average interest rate	4.57%
Long-term debt, gross	$ 1,947,000	1,882,000
Line of Credit
Long-term debt outstanding [Line Items]
Weighted average interest rate	5.79%
Long-term debt, gross	$ 169,700	46,100
Commercial paper
Long-term debt outstanding [Line Items]
Weighted average interest rate	4.76%
Long-term debt, gross	$ 81,400	144,200
Term Loan Agreements
Long-term debt outstanding [Line Items]
Weighted average interest rate	4.44%
Long-term debt, gross	$ 65,600	64,300
Medium-term notes
Long-term debt outstanding [Line Items]
Weighted average interest rate	7.32%
Long-term debt, gross	$ 35,000	35,000
Other notes
Long-term debt outstanding [Line Items]
Weighted average interest rate	6%
Long-term debt, gross	$ 346	$ 980

Debt - Long-Term Debt (Details)

Debt - Long-Term Debt (Details) $ in Thousands			12 Months Ended
	Nov. 01, 2024 USD ($)	Nov. 15, 2023 USD ($)	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Jul. 11, 2024 USD ($)	Jun. 20, 2024 USD ($)	Jun. 19, 2024 USD ($)	Apr. 01, 2024 USD ($)	Oct. 18, 2023 USD ($)	May 31, 2023 USD ($)
Long-term debt outstanding [Line Items]
Long-term debt			$ 2,292,610	$ 2,166,223
Repayments of long-term debt			$ 182,135	568,883	$ 38,764
Montana-Dakota Utilities Co.
Long-term debt outstanding [Line Items]
Ratio of total debt to total capitalization			0.48
Revolving Credit Facility | Montana-Dakota Utilities Co.
Long-term debt outstanding [Line Items]
Line of credit facility, maximum borrowing capacity										$ 200,000
Ratio of funded debt to total capitalization as specified in debt covenants			0.65
Revolving Credit Facility | Cascade Natural Gas
Long-term debt outstanding [Line Items]
Ratio of total debt to total capitalization			0.65
Revolving Credit Facility | Intermountain Gas Company
Long-term debt outstanding [Line Items]
Ratio of total debt to total capitalization			0.65
Revolving Credit Facility | MDU Resources Group, Inc.
Long-term debt outstanding [Line Items]
Long-term debt											$ 200,000
Ratio of total debt to total capitalization			0.65
Senior Notes
Long-term debt outstanding [Line Items]
Long-term debt, gross			$ 1,947,000	$ 1,882,000
Senior Notes | Montana-Dakota Utilities Co.
Long-term debt outstanding [Line Items]
Ratio of funded debt to total capitalization as specified in debt covenants						0.65
Long-term debt						$ 125,000
Interest rate, stated percentage						5.96%
Senior Notes | Cascade Natural Gas
Long-term debt outstanding [Line Items]
Total debt to total capitalization			0.50
Senior Notes | Intermountain Gas Company
Long-term debt outstanding [Line Items]
Total debt to total capitalization			0.60
Senior Notes | MDU Resources Group, Inc.
Long-term debt outstanding [Line Items]
Total debt to total capitalization			0.46
Revolving Credit Agreement | Cascade Natural Gas
Long-term debt outstanding [Line Items]
Line of credit facility, maximum borrowing capacity							$ 175,000	$ 100,000
Revolving Credit Agreement | Intermountain Gas Company
Long-term debt outstanding [Line Items]
Line of credit facility, maximum borrowing capacity							$ 175,000	$ 100,000
Term Loan Agreement | MDU Resources Group, Inc.
Long-term debt outstanding [Line Items]
Long-term debt											$ 375,000
Repayments of long-term debt	$ 190,000	$ 185,000
Term Loan Agreement | WBI Energy Transmission
Long-term debt outstanding [Line Items]
Long-term debt									$ 60,000
Interest rate, stated percentage									4.52%
Ratio of total debt to total capitalization									0.65
Debt instrument, annual principal payment									$ 4,000
Uncommitted Note Purchase And Private Shelf Agreement | WBI Energy Transmission
Long-term debt outstanding [Line Items]
Line of credit facility, maximum borrowing capacity			$ 350,000
Ratio of total debt to total capitalization			0.55
Total debt to total capitalization			0.40
Long-term debt, gross			$ 235,000
Line of credit facility, remaining borrowing capacity			$ 115,000

Debt - Schedule of Debt Maturit

Debt - Schedule of Debt Maturities (Details) $ in Thousands	Dec. 31, 2024 USD ($)
Debt Disclosure [Abstract]
2025	$ 161,700
2026	144,700
2027	24,700
2028	161,100
2029	244,400
Thereafter	$ 1,562,446

Asset Retirement Obligations (D

Asset Retirement Obligations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at beginning of year	$ 385,154	$ 373,147
Liabilities incurred	2,721	533
Liabilities settled	(5,271)	(6,633)
Accretion expense	19,655	18,894
Revisions in estimates	4,388	(787)
Balance at end of year	406,647	385,154
Plant costs/asset retirement obligations
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Accretion expense, including asset retirement obligations	$ 19,600	$ 18,900

Equity (Details)

Equity (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2024 USD ($) $ / shares shares	Dec. 31, 2023 USD ($) $ / shares shares	Dec. 31, 2022 USD ($) $ / shares
Class of Stock [Line Items]
Number of years dividends have been paid	87 years
Dividends declared per common share (in usd per share) | $ / shares	$ 0.5100	$ 0.6950	$ 0.8750
Dividends declared on common stock | $	$ 104,786	$ 142,033	$ 178,761
Credit agreement limitation on company's subsidiaries ratio of funded debt to capitalization	0.65
Company's subsidiaries net assets restricted from use for dividend payments | $	$ 1,300,000
Common Stock
Class of Stock [Line Items]
Dividends declared on common stock | $	$ 103,900	$ 141,500	$ 177,900
K-Plan
Class of Stock [Line Items]
Common stock, authorized shares remaining (in shares) | shares	7,200,000
Preferred Stock
Class of Stock [Line Items]
Preferred stock, authorized (in shares) | shares	2,000,000
Preferred stock, par value per share (in usd per share) | $ / shares	$ 100
Preferred stock, outstanding (in shares) | shares	0	0

Stock-Based Compensation - Narr

Stock-Based Compensation - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	10 Months Ended	12 Months Ended
	Oct. 30, 2024	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Share-based compensation arrangement by share-based payment award [Line Items]
Share-based compensation arrangement, number of shares available for grant (in shares)		2,300,000
Share-based compensation expense, net of tax		$ 7,100	$ 5,100	$ 6,900
Share-based compensation nonvested awards total compensation cost not yet recognized		$ 8,400
Share-based compensation, nonvested awards, total compensation cost not yet recognized, period for recognition		1 year 3 months 18 days
RSUs
Share-based compensation arrangement by share-based payment award [Line Items]
Award vesting period		3 years
Share-based payment arrangement, plan modification, incremental cost		$ 1,700
Share-based payment arrangement, plan modification, incremental cost, recognized		$ 854
Weighted average grant-date fair value (in usd per share)	$ 20.89
Share-Based Payment Arrangement
Share-based compensation arrangement by share-based payment award [Line Items]
Share-based compensation arrangement shares issued in period (in shares)		46,341	50,717	40,800
Share-based compensation arrangement, fair value		$ 850	$ 950	$ 1,200
Performance Shares
Share-based compensation arrangement by share-based payment award [Line Items]
Award vesting period			3 years
Fair value of vested shares				$ 7,600
Performance Shares | Market Condition
Share-based compensation arrangement by share-based payment award [Line Items]
Historical volatility rate		50%
Implied volatility rate		50%
Weighted average grant-date fair value (in usd per share)				$ 36.25
Performance Shares | Market Condition | Minimum
Share-based compensation arrangement by share-based payment award [Line Items]
Participant target grant of shares, percentage rate range		0%
Performance Shares | Market Condition | Maximum
Share-based compensation arrangement by share-based payment award [Line Items]
Participant target grant of shares, percentage rate range		200%
Performance Shares | Performance Condition
Share-based compensation arrangement by share-based payment award [Line Items]
Weighted average grant-date fair value (in usd per share)				$ 27.73
Performance Shares | Performance Condition | Minimum
Share-based compensation arrangement by share-based payment award [Line Items]
Participant target grant of shares, percentage rate range		0%
Performance Shares | Performance Condition | Maximum
Share-based compensation arrangement by share-based payment award [Line Items]
Participant target grant of shares, percentage rate range		200%

Stock-Based Compensation - Sche

Stock-Based Compensation - Schedule of Target Grants of Restricted Stock Units (Details) - RSUs	Dec. 31, 2024 shares
Grant Date February 2023 July 2023
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Target grant of shares (in shares)	542,233
Grant Date February 2024 June 2024
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Target grant of shares (in shares)	698,284

Stock-Based Compensation - Sc_2

Stock-Based Compensation - Schedule of Restricted Stock Unit and Performance Share Awards Activity (Details) - RSUs - $ / shares	2 Months Ended	10 Months Ended
	Dec. 31, 2024	Oct. 30, 2024
Number of Shares
Nonvested at beginning of period (in shares)	1,239,412	873,300
Granted pre-separation of Everus (in shares)		478,938
Forfeited (in shares)		(112,826)
Adjustments for performance (in shares)	663,661
Vested (in shares)	(662,556)
Nonvested at end of period (in shares)	1,240,517
Weighted Average Grant-Date Fair Value
Weighted Average Grant Date Fair Value, Nonvested at beginning of period (in usd per share)		$ 21.16
Weighted Average Grant Date Fair Value, Granted (in usd per share)		20.89
Weighted Average Grant Date Fair Value, Forfeited (in usd per share)		$ 21.35
Weighted Average Grant Date Fair Value, Vested (in usd per share)	$ 12.04
Weighted Average Grant Date Fair Value, Nonvested at end of period (in usd per share)	$ 12.56

Stock-Based Compensation - Sc_3

Stock-Based Compensation - Schedule of Performance Shares Valuation Assumptions (Details) - Market Condition - Performance Shares	12 Months Ended
	Dec. 31, 2022 $ / shares
Share-based compensation arrangement by share-based payment award [Line Items]
Weighted average grant-date fair value (in usd per share)	$ 36.25
Blended volatility rate, minimum	24.07%
Blended volatility rate, maximum	31.41%
Risk-free interest rate, minimum	0.71%
Risk-free interest rate, maximum	1.68%
Weighted average discounted dividends per share (in usd per share)	$ 2.93

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Loss - Schedule of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 2,905,233	$ 3,587,129
Other comprehensive income (loss) before reclassifications	1,134	(473)
Amounts reclassified from accumulated other comprehensive loss	452	366
Other comprehensive income (loss)	1,586	(107)
Ending balance	2,690,574	2,905,233
Discontinued Operations, Disposed of by Means Other than Sale, Spinoff | Knife River Corporation
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Amounts reclassified from accumulated other comprehensive loss		12,306
Total Accumulated Other Comprehensive Loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(18,384)	(30,583)
Ending balance	(16,798)	(18,384)
Net Unrealized Loss on Derivative Instruments Qualifying as Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	0	(125)
Other comprehensive income (loss) before reclassifications	0	0
Amounts reclassified from accumulated other comprehensive loss	0	81
Other comprehensive income (loss)	0	81
Ending balance	0	0
Net Unrealized Loss on Derivative Instruments Qualifying as Hedges | Discontinued Operations, Disposed of by Means Other than Sale, Spinoff | Knife River Corporation
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Amounts reclassified from accumulated other comprehensive loss		44
Postretirement Liability Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(18,042)	(29,900)
Other comprehensive income (loss) before reclassifications	1,049	(646)
Amounts reclassified from accumulated other comprehensive loss	432	242
Other comprehensive income (loss)	1,481	(404)
Ending balance	(16,561)	(18,042)
Postretirement Liability Adjustment | Discontinued Operations, Disposed of by Means Other than Sale, Spinoff | Knife River Corporation
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Amounts reclassified from accumulated other comprehensive loss		12,262
Net Unrealized Gain (Loss) on Available- for-sale Investments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(342)	(558)
Other comprehensive income (loss) before reclassifications	85	173
Amounts reclassified from accumulated other comprehensive loss	20	43
Other comprehensive income (loss)	105	216
Ending balance	$ (237)	(342)
Net Unrealized Gain (Loss) on Available- for-sale Investments | Discontinued Operations, Disposed of by Means Other than Sale, Spinoff | Knife River Corporation
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Amounts reclassified from accumulated other comprehensive loss		$ 0

Accumulated Other Comprehensi_4

Accumulated Other Comprehensive Loss - Schedule of Reclassification Out of AOCI (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Reclassification Adjustment out of Accumulated Other Comprehensive Loss [Line Items]
Interest expense	$ (108,347)	$ (104,624)	$ (80,683)
Income taxes	17,589	10,213	6,195
Other income	41,367	33,454	3,260
Net income	281,108	414,707	$ 367,489
Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Loss [Line Items]
Net income	(452)	(366)
Reclassification adjustment for loss on derivative instruments included in net income | Reclassification out of Accumulated Other Comprehensive Income | Interest Rate Contract
Reclassification Adjustment out of Accumulated Other Comprehensive Loss [Line Items]
Interest expense	0	(96)
Income taxes	0	15
Net income	0	(81)
Amortization of postretirement liability losses included in net periodic benefit credit | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Loss [Line Items]
Income taxes	145	78
Other income	577	320
Net income	(432)	(242)
Reclassification adjustment on available-for-sale investments included in net income | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Loss [Line Items]
Income taxes	5	11
Other income	25	54
Net income	$ (20)	$ (43)

Income Taxes - Schedule of Comp

Income Taxes - Schedule of Components of Income Before Income Taxes from Continuing Operations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Income Tax Disclosure [Abstract]
United States	$ 198,662	$ 340,330	$ 123,447
Income before income taxes	$ 198,662	$ 340,330	$ 123,447

Income Taxes - Schedule of Inco

Income Taxes - Schedule of Income Tax Expense (Benefit) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Current:
Federal	$ 30,412	$ 8,271	$ (15,849)
State	3,255	3,251	1,857
Current income taxes	33,667	11,522	(13,992)
Deferred:
Federal	(17,321)	(3,331)	15,038
State	(1,805)	(125)	4,251
Investment tax credit - net	3,048	2,147	898
Deferred income taxes	(16,078)	(1,309)	20,187
Income taxes	$ 17,589	$ 10,213	$ 6,195

Income Taxes - Schedule of Co_2

Income Taxes - Schedule of Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Deferred tax assets:
Environmental compliance	$ 33,730	$ 28,873
Pension and postretirement	25,508	27,584
Compensation-related	15,651	17,106
Customer advances	9,719	8,312
Cost recovery mechanisms	7,402	5,314
Legal and environmental contingencies	5,317	4,881
Other	20,386	13,045
Total deferred tax assets	117,713	105,115
Deferred tax liabilities:
Basis differences on property, plant and equipment	426,493	404,039
Pension and postretirement	48,355	39,110
Purchased gas adjustment	20,441	34,618
Environmental compliance	17,260	16,221
Cost recovery mechanisms	19,245	22,604
Legal and environmental contingencies	6,300	5,902
Other	19,931	33,947
Total deferred tax liabilities	558,025	556,441
Valuation allowance	1,008	1,010
Net deferred income tax liability	$ 441,320	$ 452,336

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details) - State and local jurisdiction - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Carryforwards [Line Items]
Operating loss carryforwards	$ 1	$ 1
Tax credit carryforward, amount	$ 31.6	$ 33.7

Income Taxes - Schedule of Defe

Income Taxes - Schedule of Deferred Tax Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Income Tax Disclosure [Abstract]
Change in net deferred income tax liability from the preceding table	$ (11,016)
Excess deferred income tax amortization	(8,121)
Deferred taxes associated with other comprehensive income	(532)
Other	3,591
Deferred income taxes	$ (16,078)	$ (1,309)	$ 20,187

Income Taxes - Schedule of In_2

Income Taxes - Schedule of Income Tax Expense (Benefit) Statutory Rate vs Actual Rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Computed tax at federal statutory rate
Computed tax at federal statutory rate	$ 41,719	$ 71,469	$ 25,924
Federal statutory rate	21%	21%	21%
Increases (reductions) resulting from:
State income taxes, net of federal income tax	$ 4,047	$ 3,605	$ 2,484
State income taxes, net of federal income tax, rate	2%	1.10%	2%
State investment tax credit, net of federal income tax	$ 2,400	$ 1,545	$ 1,624
State investment tax credit, net of federal income tax, rate	1.20%	0.50%	1.30%
Executive compensation	$ 2,111	$ 564	$ 683
Executive compensation, rate	1.10%	0.20%	0.60%
Federal renewable energy credit	$ (16,871)	$ (15,175)	$ (15,343)
Federal renewable energy credit, rate	(8.50%)	(4.50%)	(12.40%)
Excess deferred income tax amortization	$ (8,121)	$ (8,383)	$ (9,008)
Excess deferred income tax amortization, rate	(4.10%)	(2.50%)	(7.30%)
State tax rate change	$ (2,317)	$ (9)	$ (3)
State tax rate change, rate	(1.20%)	0%	0%
Research and development tax credit	$ (1,465)	$ (1,985)	$ (1,692)
Research and development tax credit, rate	(0.70%)	(0.60%)	(1.40%)
Nonqualified benefit plans	$ (1,142)	$ (1,313)	$ 1,516
Nonqualified benefit plans, rate	(0.60%)	(0.40%)	1.20%
Tax-free debt for equity exchange	$ 0	$ (38,967)	$ 0
Tax-free debt for equity exchange, rate	0%	(11.40%)	0%
Other	$ (2,772)	$ (1,138)	$ 10
Other, rate	(1.40%)	(0.30%)	0%
Income taxes	$ 17,589	$ 10,213	$ 6,195
Total income tax expense, rate	8.80%	3.10%	5%

Cash Flow Information (Details)

Cash Flow Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Supplemental Cash Flow Information [Line Items]
Interest, net	$ 108,242	$ 112,839	$ 49,036
Income taxes paid, net	43,572	12,162	(27,884)
AFUDC borrowed	11,000	10,000	2,200
Property, plant and equipment additions in accounts payable	36,820	46,364	34,886
Right-of-use assets obtained in exchange for new operating lease liabilities	1,787	2,265	1,324
Debt for equity exchange of retained shares in Knife River	0	293,239	0
Continuing And Discontinued Operations
Supplemental Cash Flow Information [Line Items]
Income taxes paid, net	$ 80,900	$ 62,500	$ 26,400

Business Segment Data - Schedul

Business Segment Data - Schedule of Segment Reporting Information, by Segment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Business segment data [Line Items]
External operating revenues	$ 1,757,978	$ 1,803,352	$ 1,747,298
External operation and maintenance	414,491	407,081	379,951
Purchased natural gas sold	630,403	742,965	757,883
Electric fuel and purchased power	141,148	134,779	119,405
Depreciation and amortization	200,078	190,450	188,560
Taxes, other than income	106,216	103,133	100,629
Realized gain on tax-free exchange of the retained shares in Knife River	0	186,556	0
Other income	(41,367)	(33,454)	(3,260)
Interest expense	108,347	104,624	80,683
Income tax expense (benefit)	17,589	10,213	6,195
Income (loss) from continuing operations	181,073	330,117	117,252
Discontinued operations, net of tax	100,035	84,590	250,237
Net income	281,108	414,707	367,489
Capital expenditures	525,498	497,719	438,229
Assets	7,038,818	7,833,159	9,660,781
Property, plant and equipment	7,554,063	7,081,267	6,629,518
Accumulated depreciation and amortization	2,209,771	2,076,375	1,963,260
Additional information [Abstract]
Net noncash acquisitions, capital expenditure-related accounts payable and AFUDC	7,100	(13,600)	4,400
Operating Segments
Business segment data [Line Items]
External operating revenues	1,827,402	1,866,324	1,806,456
Assets	6,892,959	6,564,962	6,061,151
Operating Segments | Electric
Business segment data [Line Items]
External operating revenues	414,406	401,037	377,015
External operation and maintenance	94,897	92,521	93,236
Purchased natural gas sold	0	0	0
Electric fuel and purchased power	141,148	134,779	119,405
Depreciation and amortization	66,524	64,253	67,802
Taxes, other than income	17,605	16,695	16,917
Realized gain on tax-free exchange of the retained shares in Knife River		0
Other income	(8,205)	(5,815)	(528)
Interest expense	30,058	28,064	28,526
Income tax expense (benefit)	(2,414)	(1,019)	(5,420)
Income (loss) from continuing operations	74,793	71,559	57,077
Discontinued operations, net of tax	0	0	0
Net income	74,793	71,559	57,077
Capital expenditures	110,812	109,805	133,970
Assets	1,976,912	1,955,644	1,856,258
Property, plant and equipment	2,480,816	2,369,039	2,276,613
Accumulated depreciation and amortization	716,736	660,438	625,813
Operating Segments | Natural gas distribution
Business segment data [Line Items]
External operating revenues	1,200,975	1,287,236	1,273,588
External operation and maintenance	231,087	219,481	205,009
Purchased natural gas sold	630,403	742,965	757,883
Electric fuel and purchased power	0	0	0
Depreciation and amortization	101,958	95,300	89,466
Taxes, other than income	76,042	75,207	71,095
Realized gain on tax-free exchange of the retained shares in Knife River		0
Other income	(25,509)	(20,867)	(3,213)
Interest expense	63,185	57,601	42,126
Income tax expense (benefit)	7,974	6,927	7,805
Income (loss) from continuing operations	46,937	48,520	45,171
Discontinued operations, net of tax	0	0	0
Net income	46,937	48,520	45,171
Capital expenditures	286,152	274,836	240,064
Assets	3,730,532	3,532,142	3,214,452
Property, plant and equipment	3,731,093	3,462,187	3,208,059
Accumulated depreciation and amortization	1,139,223	1,068,037	1,009,788
Operating Segments | Pipeline
Business segment data [Line Items]
External operating revenues	142,597	115,079	96,695
External operation and maintenance	75,456	70,386	60,300
Purchased natural gas sold	0	0	0
Electric fuel and purchased power	0	0	0
Depreciation and amortization	29,362	26,811	26,857
Taxes, other than income	12,175	10,822	12,318
Realized gain on tax-free exchange of the retained shares in Knife River		0
Other income	(5,850)	(3,675)	(1,272)
Interest expense	10,862	9,428	9,966
Income tax expense (benefit)	17,470	12,409	10,522
Income (loss) from continuing operations	68,042	47,375	36,194
Discontinued operations, net of tax	0	(457)	(906)
Net income	68,042	46,918	35,288
Capital expenditures	126,806	115,903	61,923
Assets	1,151,317	1,045,704	961,893
Property, plant and equipment	1,338,006	1,218,387	1,108,141
Accumulated depreciation and amortization	351,045	328,010	308,516
Operating Segments | Other
Business segment data [Line Items]
External operating revenues	0	0	0
External operation and maintenance	13,051	24,693	21,406
Purchased natural gas sold	0	0	0
Electric fuel and purchased power	0	0	0
Depreciation and amortization	2,234	4,086	4,435
Taxes, other than income	394	409	299
Other income	(1,803)	(3,097)	1,753
Interest expense	4,242	9,531	65
Income tax expense (benefit)	(5,441)	(8,104)	(6,712)
Income (loss) from continuing operations	(8,699)	162,663	(21,190)
Discontinued operations, net of tax	100,035	85,047	251,143
Net income	91,336	247,710	229,953
Capital expenditures	1,728	(2,825)	2,272
Assets	180,057	1,299,669	3,628,178
Property, plant and equipment	4,148	31,654	36,705
Accumulated depreciation and amortization	2,767	19,890	19,143
Intersegment eliminations
Business segment data [Line Items]
External operating revenues	(69,619)	(63,091)	(59,244)
External operation and maintenance	(721)	(989)	(998)
Purchased natural gas sold	(68,898)	(62,102)	(58,246)
Other income	15,453	13,648	636
Interest expense	(15,453)	(13,648)	(636)
Assets	(379,399)	(579,235)	(1,184,512)
Intersegment eliminations | Electric
Business segment data [Line Items]
External operating revenues	(72)	(138)	(58)
External operation and maintenance	(72)	(138)	(58)
Purchased natural gas sold	0	0	0
Other income	0	0	0
Interest expense	0	0	0
Intersegment eliminations | Natural gas distribution
Business segment data [Line Items]
External operating revenues	(130)	(301)	(216)
External operation and maintenance	(130)	(301)	(216)
Purchased natural gas sold	(68,898)	(62,102)	(58,246)
Other income	0	0	0
Interest expense	0	0	0
Intersegment eliminations | Pipeline
Business segment data [Line Items]
External operating revenues	(69,222)	(62,533)	(58,884)
External operation and maintenance	(324)	(431)	(638)
Purchased natural gas sold	0	0	0
Other income	655	217	80
Interest expense	(4,633)	(3,842)	(136)
Intersegment eliminations | Other
Business segment data [Line Items]
External operating revenues	(195)	(119)	(86)
External operation and maintenance	(195)	(119)	(86)
Purchased natural gas sold	0	0	0
Other income	14,798	13,431	556
Interest expense	$ (10,820)	$ (9,806)	$ (500)

Business Segment Data - Sched_2

Business Segment Data - Schedule of Operating Revenues and Operating Assets Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Segment Reporting, Revenue Reconciling Item [Line Items]
External operating revenues	$ 1,757,978	$ 1,803,352	$ 1,747,298
Assets	7,038,818	7,833,159	9,660,781
Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
External operating revenues	1,827,402	1,866,324	1,806,456
Assets	6,892,959	6,564,962	6,061,151
Other
Segment Reporting, Revenue Reconciling Item [Line Items]
External operating revenues	195	119	86
Assets	525,258	1,847,432	4,784,142
Intersegment eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
External operating revenues	(69,619)	(63,091)	(59,244)
Assets	$ (379,399)	$ (579,235)	$ (1,184,512)

Employee Benefit Plans - Change

Employee Benefit Plans - Change in Benefit Obligations and Plan Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Pension Benefits
Change in benefit obligation:
Benefit obligation at beginning of year	$ 275,586	$ 278,286
Service cost	0	0	$ 0
Interest cost	12,799	13,521	9,396
Plan participants' contributions	0	0
Actuarial (gain) loss	(11,040)	5,395
Benefits paid	(21,995)	(21,616)
Benefit obligation at end of year	255,350	275,586	278,286
Change in net plan assets:
Fair value of plan assets at beginning of year	248,558	242,031
Actual return on plan assets	1,152	20,576
Employer contribution	2,911	7,567
Plan participants' contributions	0	0
Benefits paid	(21,995)	(21,616)
Fair value of net plan assets at end of year	230,626	248,558	242,031
Funded status - (under) over	(24,724)	(27,028)
Amounts recognized in the Consolidated Balance Sheets at December 31:
Noncurrent assets - other	0	0
Noncurrent liabilities - other	24,724	27,028
Benefit obligation (liabilities) assets - net amount recognized	(24,724)	(27,028)
Amounts recognized in accumulated other comprehensive loss:
Actuarial loss (gain)	13,228	32,273
Prior service credit	0	0
Total	13,228	32,273
Amounts recognized in regulatory assets or liabilities:
Actuarial loss (gain)	139,962	140,232
Prior service credit	0	0
Total	139,962	140,232
Other Postretirement Benefits
Change in benefit obligation:
Benefit obligation at beginning of year	39,590	40,315
Service cost	505	534	894
Interest cost	1,837	1,956	1,383
Plan participants' contributions	412	479
Actuarial (gain) loss	(3,420)	(215)
Benefits paid	(3,249)	(3,479)
Benefit obligation at end of year	35,675	39,590	40,315
Change in net plan assets:
Fair value of plan assets at beginning of year	79,234	76,640
Actual return on plan assets	2,297	5,518
Employer contribution	71	76
Plan participants' contributions	412	479
Benefits paid	(3,249)	(3,479)
Fair value of net plan assets at end of year	78,765	79,234	$ 76,640
Funded status - (under) over	43,090	39,644
Amounts recognized in the Consolidated Balance Sheets at December 31:
Noncurrent assets - other	43,090	39,644
Noncurrent liabilities - other	0	0
Benefit obligation (liabilities) assets - net amount recognized	43,090	39,644
Amounts recognized in accumulated other comprehensive loss:
Actuarial loss (gain)	(809)	(3,515)
Prior service credit	(37)	(115)
Total	(846)	(3,630)
Amounts recognized in regulatory assets or liabilities:
Actuarial loss (gain)	(1,478)	(1,146)
Prior service credit	(1,303)	(2,619)
Total	$ (2,781)	$ (3,765)

Employee Benefit Plans - Benefi

Employee Benefit Plans - Benefit Obligations in Excess of Plan Assets (Details) - Pension Benefits - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	$ 255,350	$ 275,586
Accumulated benefit obligation	255,350	275,586
Fair value of plan assets	$ 230,626	$ 248,558

Employee Benefit Plans - Compon

Employee Benefit Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Pension Benefits
Components of net periodic benefit cost (credit):
Service cost	$ 0	$ 0	$ 0
Interest cost	12,799	13,521	9,396
Expected return on assets	(16,113)	(17,194)	(17,482)
Amortization of prior service credit	0	0	0
Recognized net actuarial loss (gain)	4,149	3,093	5,826
Net periodic benefit cost (credit), including amount capitalized	835	(580)	(2,260)
Less amount capitalized	0	0	0
Net periodic benefit cost	835	(580)	(2,260)
Other changes in plan assets and benefit obligations recognized in accumulated comprehensive loss:
Net loss (gain)	401	187	2,369
Amortization of actuarial (loss) gain	(359)	(292)	(1,310)
Amortization of prior service credit	0	0	0
Reclassification of postretirement liability adjustment from regulatory asset	0	0	5,343
Total recognized in accumulated other comprehensive loss	42	(105)	6,402
Other changes in plan assets and benefit obligations recognized in regulatory assets or liabilities:
Net loss (gain)	3,520	1,826	9,757
Amortization of actuarial (loss) gain	(3,790)	(2,801)	(5,373)
Amortization of prior service credit	0	0	0
Reclassification of postretirement liability adjustment from regulatory asset	0	0	(5,343)
Total recognized in regulatory assets or liabilities	(270)	(975)	(959)
Total recognized in net periodic benefit credit, accumulated other comprehensive loss and regulatory assets or liabilities	607	(1,660)	3,183
Other Postretirement Benefits
Components of net periodic benefit cost (credit):
Service cost	505	534	894
Interest cost	1,837	1,956	1,383
Expected return on assets	(5,315)	(5,361)	(5,277)
Amortization of prior service credit	(1,318)	(1,318)	(1,318)
Recognized net actuarial loss (gain)	(288)	(504)	(570)
Net periodic benefit cost (credit), including amount capitalized	(4,579)	(4,693)	(4,888)
Less amount capitalized	0	107	175
Net periodic benefit cost	(4,579)	(4,800)	(5,063)
Other changes in plan assets and benefit obligations recognized in accumulated comprehensive loss:
Net loss (gain)	71	(604)	(4,141)
Amortization of actuarial (loss) gain	130	108	(281)
Amortization of prior service credit	45	78	125
Reclassification of postretirement liability adjustment from regulatory asset	0	0	(992)
Total recognized in accumulated other comprehensive loss	246	(418)	(5,289)
Other changes in plan assets and benefit obligations recognized in regulatory assets or liabilities:
Net loss (gain)	(472)	(107)	11,920
Amortization of actuarial (loss) gain	158	304	500
Amortization of prior service credit	1,273	1,273	1,273
Reclassification of postretirement liability adjustment from regulatory asset	0	0	992
Total recognized in regulatory assets or liabilities	959	1,470	14,685
Total recognized in net periodic benefit credit, accumulated other comprehensive loss and regulatory assets or liabilities	$ (3,374)	$ (3,748)	$ 4,333

Employee Benefit Plans - Weight

Employee Benefit Plans - Weighted Average Assumptions (Details)	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Pension Benefits
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Discount rate	5.41%	4.84%
Expected return on plan assets	6.50%	6.50%
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount rate	4.84%	5.06%
Expected return on plan assets	6.50%	6.50%
Other Postretirement Benefits
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Discount rate	5.43%	4.85%
Expected return on plan assets	6%	6%
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount rate	4.85%	5.07%
Expected return on plan assets	6%	6%

Employee Benefit Plans - Narrat

Employee Benefit Plans - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Defined Benefit Plan Disclosure [Line Items]
Nonqualified defined contribution plan, cost	$ 4,000	$ 2,700	$ 538
Defined Contribution Plan
Defined Benefit Plan Disclosure [Line Items]
Nonqualified defined contribution plan, cost	10,700	$ 17,000	$ 14,300
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Expected future employer contributions, next fiscal year	1,700
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Expected future employer contributions, next fiscal year	$ 18
Minimum
Defined Benefit Plan Disclosure [Line Items]
Multiemployer plan yellow zone status funded percentage	65%
Multiemployer plan green zone status funded percentage	80%
Minimum | Equity securities | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, target allocation, percentage	40%
Minimum | Equity securities | Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, target allocation, percentage	10%
Minimum | Fixed Income Securities | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, target allocation, percentage	50%
Minimum | Fixed Income Securities | Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, target allocation, percentage	80%
Maximum
Defined Benefit Plan Disclosure [Line Items]
Multiemployer plan red zone status funded percentage	65%
Multiemployer plan yellow status funded percentage	80%
Maximum | Equity securities | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, target allocation, percentage	50%
Maximum | Equity securities | Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, target allocation, percentage	20%
Maximum | Fixed Income Securities | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, target allocation, percentage	60%
Maximum | Fixed Income Securities | Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, target allocation, percentage	90%

Employee Benefit Plans - Health

Employee Benefit Plans - Health Care Rate Assumptions and Cost Trend Rate (Details) - Other Postretirement Benefits	Dec. 31, 2024	Dec. 31, 2023
Defined Benefit Plan Disclosure [Line Items]
Health care cost trend rate - ultimate	4.50%	4.50%
Pre-65
Defined Benefit Plan Disclosure [Line Items]
Health care trend rate assumed for next year (pre-65/post-65)	8.50%	7.50%
Post-65
Defined Benefit Plan Disclosure [Line Items]
Health care trend rate assumed for next year (pre-65/post-65)	6.25%	6.50%

Employee Benefit Plans - Estima

Employee Benefit Plans - Estimated Future Benefit Payments and Subsidies (Details) $ in Thousands	Dec. 31, 2024 USD ($)
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
2025	$ 22,280
2026	22,070
2027	21,870
2028	21,500
2029	21,170
2030-2034	98,020
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
2025	3,333
2026	3,235
2027	3,153
2028	3,064
2029	2,941
2030-2034	13,659
2025	48
2026	43
2027	37
2028	32
2029	27
2030-2034	$ 85

Employee Benefit Plans - Pensio

Employee Benefit Plans - Pension Fair Value (Details) - Pension Benefits - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Defined Benefit Plan Disclosure [Line Items]
Total assets measured at fair value	$ 230,626	$ 248,558	$ 242,031
Cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Investment within plan asset category, percentage	1%	7%
U.S. Government securities
Defined Benefit Plan Disclosure [Line Items]
Investment within plan asset category, percentage	19%	7%
Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Investment within plan asset category, percentage	39%	51%
Other investments
Defined Benefit Plan Disclosure [Line Items]
Investment within plan asset category, percentage	17%	9%
International companies
Defined Benefit Plan Disclosure [Line Items]
Investment within plan asset category, percentage	15%	15%
US, large cap companies
Defined Benefit Plan Disclosure [Line Items]
Investment within plan asset category, percentage	9%	11%
Fair Value, Inputs, Level 1, Level 2, and Level 3 | Cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Total assets measured at fair value	$ 4,512	$ 7,197
Fair Value, Inputs, Level 1, Level 2, and Level 3 | U.S. companies
Defined Benefit Plan Disclosure [Line Items]
Total assets measured at fair value	(2)	(2)
Fair Value, Inputs, Level 1, Level 2, and Level 3 | Collective and mutual funds
Defined Benefit Plan Disclosure [Line Items]
Total assets measured at fair value	166,383	172,980
Fair Value, Inputs, Level 1, Level 2, and Level 3 | U.S. Government securities
Defined Benefit Plan Disclosure [Line Items]
Total assets measured at fair value	59,473	63,303
Quoted Prices in Active Markets for Identical Assets  (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Total assets measured at fair value	106,391	114,921
Quoted Prices in Active Markets for Identical Assets  (Level 1) | Cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Total assets measured at fair value	0	0
Quoted Prices in Active Markets for Identical Assets  (Level 1) | U.S. companies
Defined Benefit Plan Disclosure [Line Items]
Total assets measured at fair value	(2)	(2)
Quoted Prices in Active Markets for Identical Assets  (Level 1) | Collective and mutual funds
Defined Benefit Plan Disclosure [Line Items]
Total assets measured at fair value	72,777	84,761
Quoted Prices in Active Markets for Identical Assets  (Level 1) | U.S. Government securities
Defined Benefit Plan Disclosure [Line Items]
Total assets measured at fair value	33,616	30,162
Significant Other Observable Inputs  (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Total assets measured at fair value	123,975	128,557
Significant Other Observable Inputs  (Level 2) | Cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Total assets measured at fair value	4,512	7,197
Significant Other Observable Inputs  (Level 2) | U.S. companies
Defined Benefit Plan Disclosure [Line Items]
Total assets measured at fair value	0	0
Significant Other Observable Inputs  (Level 2) | Collective and mutual funds
Defined Benefit Plan Disclosure [Line Items]
Total assets measured at fair value	93,606	88,219
Significant Other Observable Inputs  (Level 2) | U.S. Government securities
Defined Benefit Plan Disclosure [Line Items]
Total assets measured at fair value	25,857	33,141
Significant Unobservable Inputs  (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Total assets measured at fair value	0	0
Significant Unobservable Inputs  (Level 3) | Cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Total assets measured at fair value	0	0
Significant Unobservable Inputs  (Level 3) | U.S. companies
Defined Benefit Plan Disclosure [Line Items]
Total assets measured at fair value	0	0
Significant Unobservable Inputs  (Level 3) | Collective and mutual funds
Defined Benefit Plan Disclosure [Line Items]
Total assets measured at fair value	0	0
Significant Unobservable Inputs  (Level 3) | U.S. Government securities
Defined Benefit Plan Disclosure [Line Items]
Total assets measured at fair value	0	0
Fair Value Measured at Net Asset Value Per Share
Defined Benefit Plan Disclosure [Line Items]
Total assets measured at fair value	$ 260	$ 5,080

Employee Benefit Plans - Other

Employee Benefit Plans - Other Postretirement Fair value (Details) - Other Postretirement Benefits - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Defined Benefit Plan Disclosure [Line Items]
Total assets measured at fair value	$ 78,765	$ 79,234	$ 76,640
Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Postretirement investments in insurance contracts, percentage	41%	60%
US, large cap companies
Defined Benefit Plan Disclosure [Line Items]
Postretirement investments in insurance contracts, percentage	19%	16%
U.S. Government securities
Defined Benefit Plan Disclosure [Line Items]
Postretirement investments in insurance contracts, percentage	28%	15%
US, small cap companies
Defined Benefit Plan Disclosure [Line Items]
Postretirement investments in insurance contracts, percentage	6%	5%
Other investments
Defined Benefit Plan Disclosure [Line Items]
Postretirement investments in insurance contracts, percentage	6%	4%
Fair Value, Inputs, Level 1, Level 2, and Level 3 | Cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Total assets measured at fair value	$ 4,373	$ 4,562
Fair Value, Inputs, Level 1, Level 2, and Level 3 | U.S. companies
Defined Benefit Plan Disclosure [Line Items]
Total assets measured at fair value	2,880	2,369
Fair Value, Inputs, Level 1, Level 2, and Level 3 | Insurance contract
Defined Benefit Plan Disclosure [Line Items]
Total assets measured at fair value	71,512	72,303
Quoted Prices in Active Markets for Identical Assets  (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Total assets measured at fair value	2,880	2,369
Quoted Prices in Active Markets for Identical Assets  (Level 1) | Cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Total assets measured at fair value	0	0
Quoted Prices in Active Markets for Identical Assets  (Level 1) | U.S. companies
Defined Benefit Plan Disclosure [Line Items]
Total assets measured at fair value	2,880	2,369
Quoted Prices in Active Markets for Identical Assets  (Level 1) | Insurance contract
Defined Benefit Plan Disclosure [Line Items]
Total assets measured at fair value	0	0
Significant Other Observable Inputs  (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Total assets measured at fair value	75,885	76,865
Significant Other Observable Inputs  (Level 2) | Cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Total assets measured at fair value	4,373	4,562
Significant Other Observable Inputs  (Level 2) | U.S. companies
Defined Benefit Plan Disclosure [Line Items]
Total assets measured at fair value	0	0
Significant Other Observable Inputs  (Level 2) | Insurance contract
Defined Benefit Plan Disclosure [Line Items]
Total assets measured at fair value	71,512	72,303
Significant Unobservable Inputs  (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Total assets measured at fair value	0	0
Significant Unobservable Inputs  (Level 3) | Cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Total assets measured at fair value	0	0
Significant Unobservable Inputs  (Level 3) | U.S. companies
Defined Benefit Plan Disclosure [Line Items]
Total assets measured at fair value	0	0
Significant Unobservable Inputs  (Level 3) | Insurance contract
Defined Benefit Plan Disclosure [Line Items]
Total assets measured at fair value	$ 0	$ 0

Employee Benefit Plans - Nonqua

Employee Benefit Plans - Nonqualified Benefit Plans Benefit Obligations (Details) - Supplemental Employee Retirement Plan - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	$ 52,007	$ 57,033
Accumulated benefit obligation	$ 52,007	$ 57,033

Employee Benefit Plans - Nonq_2

Employee Benefit Plans - Nonqualified Benefit Plans Components of NPBC (Details) - Supplemental Employee Retirement Plan - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 2,568	$ 2,740	$ 1,681
Recognized net actuarial loss	365	273	911
Net periodic benefit cost	$ 2,933	$ 3,013	$ 2,592

Employee Benefit Plans - Nonq_3

Employee Benefit Plans - Nonqualified Benefit Plans Weighted Average Assumptions (Details) - Supplemental Employee Retirement Plan	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation discount rate	5.26%	4.73%
Net periodic benefit cost discount rate	4.73%	4.97%

Employee Benefit Plans - Nonq_4

Employee Benefit Plans - Nonqualified Benefit Plans Future Benefit Payments (Details) - Supplemental Employee Retirement Plan $ in Thousands	Dec. 31, 2024 USD ($)
Defined Benefit Plan Disclosure [Line Items]
2025	$ 5,700
2026	5,610
2027	5,830
2028	5,560
2029	5,190
2030-2034	$ 20,920

Employee Benefit Plans - Nonq_5

Employee Benefit Plans - Nonqualified Benefit Plans Investments (Details) - Supplemental Employee Retirement Plan - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Defined Benefit Plan Disclosure [Line Items]
Total investments	$ 102,995	$ 100,648
Insurance contracts
Defined Benefit Plan Disclosure [Line Items]
Total investments	59,282	62,936
Life insurance
Defined Benefit Plan Disclosure [Line Items]
Total investments	30,834	31,303
Other
Defined Benefit Plan Disclosure [Line Items]
Total investments	$ 12,879	$ 6,409

Employee Benefit Plans - Multie

Employee Benefit Plans - Multiemployer Plans Participation by Plan (Details) - Pension Benefits - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Multiemployer Plans [Line Items]
Total contributions	$ 1,434	$ 1,690	$ 1,613
Idaho Plumbers and Pipefitters Pension Plan
Multiemployer Plans [Line Items]
Employer identification number	826010346
Pension plan number	001
Pension Protection Act Zone Status	Green	Green
Pension Protection Act Zone Status, Date	May 31, 2024	May 31, 2023
FIP/RP Status Pending/Implemented	No
Contributions	$ 1,434	$ 1,690	$ 1,613
Surcharge Imposed	No
Expiration Date of Collective Bargaining Agreement	Mar. 31, 2027

Regulatory Matters - MTPSC (Det

Regulatory Matters - MTPSC (Details) - Montana-Dakota Utilities Co. - Natural gas distribution - MTPSC - USD ($) $ in Millions	Jan. 14, 2025	Oct. 15, 2024	Jul. 15, 2024
Public Utilities, General Disclosures [Line Items]
Public utilities, requested rate increase (decrease), amount		$ 8	$ 9.4
Public utilities, requested rate increase (decrease), percentage		10.20%	11.10%
Subsequent Event
Public Utilities, General Disclosures [Line Items]
Public utilities, interim rate increase (decrease), amount	$ 7.7

Regulatory Matters - NDPSC (Det

Regulatory Matters - NDPSC (Details) - NDPSC - Montana-Dakota Utilities Co. - USD ($) $ in Millions	Nov. 01, 2024	Dec. 13, 2023	Nov. 01, 2023	Sep. 16, 2024
Public Utilities, General Disclosures [Line Items]
Public utilities, annual revenue increase (decrease)				$ 9.4
Public utilities, annual revenue increase (decrease), percentage				6.10%
Natural gas distribution
Public Utilities, General Disclosures [Line Items]
Public utilities, requested rate increase (decrease), amount			$ 11.6
Public utilities, requested rate increase (decrease), percentage			7.50%
Public utilities, interim rate increase (decrease), amount		$ 10.1
Public utilities, interim rate increase (decrease), percentage		6.50%
Electric
Public Utilities, General Disclosures [Line Items]
Requested renewable resource cost adjustment rate tariff	$ 18.3
Public utilities, approved rate increase (decrease), amount	$ 2.8

Regulatory Matters - WUTC (Deta

Regulatory Matters - WUTC (Details) - Natural gas distribution - WUTC - Cascade Natural Gas - USD ($) $ in Millions	Dec. 11, 2024	Mar. 29, 2024
Pending Rate Case, Multi-Year, Year One
Public Utilities, General Disclosures [Line Items]
Public utilities, requested rate increase (decrease), amount	$ 29.8	$ 43.8
Public utilities, requested rate increase (decrease), percentage	7.90%	11.60%
Pending Rate Case, Multi-Year, Year Two
Public Utilities, General Disclosures [Line Items]
Public utilities, requested rate increase (decrease), amount	$ 10.8	$ 11.7
Public utilities, requested rate increase (decrease), percentage	2.60%	2.80%

Regulatory matters - WYPSC (Det

Regulatory matters - WYPSC (Details) - Natural gas distribution - WYPSC - Montana-Dakota Utilities Co. - Pending Rate Case $ in Millions	Oct. 31, 2024 USD ($)
Public Utilities, General Disclosures [Line Items]
Public utilities, requested rate increase (decrease), amount	$ 2.6
Public utilities, requested rate increase (decrease), percentage	14%

Regulatory Matters - FERC (Deta

Regulatory Matters - FERC (Details) $ in Millions	Aug. 29, 2024 USD ($)
FERC | Montana-Dakota Utilities Co. | Transmission Formula
Public Utilities, General Disclosures [Line Items]
Public utilities, requested rate increase (decrease), amount	$ 19.7

Commitments and Contingencies -

Commitments and Contingencies - Litigation (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Commitments and Contingencies Disclosure [Abstract]
Potential liabilities related to litigation and environmental matters	$ 24,100	$ 22,500
Loss contingency, receivable	24	152
Loss contingency, regulatory asset	$ 22,900	$ 21,600

Commitments and Contingencies_2

Commitments and Contingencies - Environmental matters (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2024 USD ($)
Missoula, MT manufactured gas plant site
Site Contingency [Line Items]
Total estimated costs for site remediation	$ 560
Environmental matters estimated investigative costs	2,000
Environmental matters accrual for site remediation	645
Incurred costs for site remedial investigation	1,200
Bremerton, WA manufactured gas plant site
Site Contingency [Line Items]
Environmental matters accrual for site remediation	17,500
Total estimated costs for site remedial investigation and feasibility study	16,000
Incurred costs for site remedial investigation and feasibility study	11,700
Environmental matters accrual of investigative costs	4,300
Bellingham, WA manufactured gas plant site
Site Contingency [Line Items]
Site contingency, loss exposure not accrued, preferred alternative estimate	9,300
Minimum | Bremerton, WA manufactured gas plant site
Site Contingency [Line Items]
Site contingency, loss exposure not accrued, best estimate	13,600
Minimum | Bellingham, WA manufactured gas plant site
Site Contingency [Line Items]
Site contingency, loss exposure not accrued, best estimate	8,000
Maximum | Bremerton, WA manufactured gas plant site
Site Contingency [Line Items]
Site contingency, loss exposure not accrued, best estimate	71,500
Maximum | Bellingham, WA manufactured gas plant site
Site Contingency [Line Items]
Site contingency, loss exposure not accrued, best estimate	$ 20,400

Commitments and Contingencies_3

Commitments and Contingencies - Purchase Commitments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Long-term Purchase Commitment [Line Items]
Commitment term	35 years
Amounts purchased under various commitments	$ 841,700	$ 1,000,000	$ 870,600
Inventories
Purchase commitments due
2025	658,012
2026	310,894
2027	210,152
2028	177,613
2029	147,081
Thereafter	$ 1,221,125

Commitments and Contingencies_4

Commitments and Contingencies - Guarantees (Details)	Dec. 31, 2024 USD ($)
Guarantor Obligations [Line Items]
Letters of credit set to expire in next fiscal year	$ 14,300,000
Outstanding letters of credit	0
Amount of surety bonds outstanding	15,600,000
Line of Credit
Guarantor Obligations [Line Items]
Line of credit facility, maximum borrowing capacity	$ 14,300,000

Commitments and Contingencies_5

Commitments and Contingencies - Leases (Details)	Dec. 31, 2024
Loss Contingencies [Line Items]
Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Other accrued liabilities
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Other
Vehicles and Equipment
Loss Contingencies [Line Items]
Remaining lease term	5 years
Buildings and Easements
Loss Contingencies [Line Items]
Remaining lease term	35 years

Commitments and Contingencies_6

Commitments and Contingencies - Schedule of Lease Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Leases [Abstract]
Short-term lease cost	$ 1,549	$ 1,646	$ 1,373
Operating lease cost	3,069	2,871	2,497
Variable lease cost	819	676	413
Total lease costs	$ 5,437	$ 5,193	$ 4,283
Weighted average remaining lease term	12 years 7 months 24 days	15 years 4 months 6 days	15 years 1 month 24 days
Weighted average discount rate	6.08%	4.88%	4.65%
Cash paid for amounts included in the measurement of lease liabilities	$ 3,063	$ 2,868	$ 2,500

Commitments and Contingencies_7

Commitments and Contingencies - Schedule of Operating Lease Liabilities Undiscounted Cash Flows Maturity (Details) $ in Thousands	Dec. 31, 2024 USD ($)
Leases [Abstract]
2025	$ 3,034
2026	2,648
2027	2,011
2028	1,570
2029	1,492
Thereafter	20,808
Total	31,563
Less discount	10,654
Total operating lease liabilities	$ 20,909

Commitments and Contingencies_8

Commitments and Contingencies - Variable Interest Entities (Details) $ in Millions	Dec. 31, 2024 USD ($)
Fuel Contract
Variable Interest Entities [Line Items]
Variable interest entity, reporting entity involvement, maximum loss exposure, amount	$ 25.6

Subsequent Events (Details)

Subsequent Events (Details) - Jointly Owned Electricity Generation Plant - Badger Wind LLC - Subsequent Event $ in Millions	Feb. 13, 2025 USD ($) MW
Subsequent Event [Line Items]
Proportionate ownership share	49%
Net generating capacity	250
Payments to purchase ownership | $	$ 294
Wind generation ownership	122.5

Schedule I - Condensed Financ_2

Schedule I - Condensed Financial Information of Registrant - Condensed Statements of Income and Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Condensed Financial Statements, Captions [Line Items]
Revenues from contracts with customers	$ 1,752,995	$ 1,805,807	$ 1,754,158
Operating expenses	1,492,336	1,578,408	1,546,428
Operating income	265,642	224,944	200,870
Realized gain on tax-free exchange of the retained shares in Knife River	0	186,556	0
Interest expense	108,347	104,624	80,683
Income before income taxes	198,662	340,330	123,447
Income taxes	17,589	10,213	6,195
Income from continuing operations	181,073	330,117	117,252
Discontinued operations, net of tax	100,035	84,590	250,237
Net income	281,108	414,707	367,489
Comprehensive income attributable to common stockholders	282,694	414,600	377,910
MDU Resources Group, Inc.
Condensed Financial Statements, Captions [Line Items]
Revenues from contracts with customers	0	0	0
Operating expenses	4,416	9,668	1,636
Operating income	(4,416)	(9,668)	(1,636)
Realized gain on tax-free exchange of the retained shares in Knife River	0	186,556	0
Interest expense	642	7,109	0
Income before income taxes	(5,058)	169,779	(1,636)
Income taxes	(2,324)	(4,220)	(400)
Equity in earnings of subsidiaries from continuing operations	183,807	156,118	118,488
Income from continuing operations	181,073	330,117	117,252
Equity in earnings of subsidiaries from discontinued operations	140,042	143,181	261,701
Discontinued operations, net of tax	(40,007)	(58,591)	(11,464)
Net income	281,108	414,707	367,489
Comprehensive income attributable to common stockholders	$ 282,694	$ 414,600	$ 377,910

Schedule I - Condensed Financ_3

Schedule I - Condensed Financial Information of Registrant - Condensed Balance Sheets (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Current assets:
Cash and cash equivalents	$ 66,904	$ 60,473
Receivables, net	274,303	250,153
Prepayments and other current assets	64,676	66,431
Total current assets	666,259	1,363,723
Noncurrent assets
Investments	115,459	112,475
Other	244,722	211,369
Total noncurrent assets	6,372,559	6,469,436
Total assets	7,038,818	7,833,159	$ 9,660,781
Current liabilities:
Accounts payable	150,070	159,975
Taxes payable	43,372	49,553
Dividends payable	26,511	25,461
Accrued compensation	35,264	40,792
Other accrued liabilities	124,514	129,592
Total current liabilities	678,598	1,075,733
Noncurrent liabilities:
Long-term debt, net of debt issuance costs	2,130,910	2,104,904
Other	231,895	209,882
Total noncurrent liabilities	3,669,646	3,852,193
Commitments and contingencies
Stockholders' equity:
Common stock Authorized - 500,000,000 shares, $1.00 par value Shares issued - 203,934,578 at December 31, 2024 and 203,689,090 at December 31, 2023	203,935	203,689
Other paid-in capital	1,473,738	1,466,235
Retained earnings	1,029,699	1,253,693
Accumulated other comprehensive loss	(16,798)	(18,384)
Total stockholders' equity	2,690,574	2,905,233	3,587,129	$ 3,382,874
Total liabilities and stockholders' equity	7,038,818	7,833,159
MDU Resources Group, Inc.
Current assets:
Cash and cash equivalents	29,361	33,039	$ 19,486	$ 6,159
Receivables, net	2,777	6,568
Taxes receivable	5,799	0
Prepayments and other current assets	3,210	8,261
Total current assets	73,102	78,394
Noncurrent assets
Investments	37,264	37,722
Deferred income taxes	13,569	12,596
Operating lease right-of-use assets	160	31
Other	2,874	2,593
Total noncurrent assets	2,915,178	3,257,064
Total assets	2,988,280	3,335,458
Current liabilities:
Accounts payable	4,076	4,264
Taxes payable	0	542
Dividends payable	26,511	25,461
Accrued compensation	7,939	9,651
Operating lease liabilities due within one year	60	25
Other accrued liabilities	7,653	8,008
Total current liabilities	245,351	185,493
Noncurrent liabilities:
Long-term debt, net of debt issuance costs	(536)	57,048
Operating lease liabilities	100	6
Other	52,791	187,678
Total noncurrent liabilities	52,355	244,732
Commitments and contingencies
Stockholders' equity:
Common stock Authorized - 500,000,000 shares, $1.00 par value Shares issued - 203,934,578 at December 31, 2024 and 203,689,090 at December 31, 2023	203,935	203,689
Other paid-in capital	1,473,738	1,466,235
Retained earnings	1,029,699	1,253,693
Accumulated other comprehensive loss	(16,798)	(18,384)
Total stockholders' equity	2,690,574	2,905,233
Total liabilities and stockholders' equity	2,988,280	3,335,458
MDU Resources Group, Inc. | Subsidiaries
Current assets:
Receivables, net	31,955	30,526
Noncurrent assets
Investments	2,861,311	3,146,122
Notes receivable from subsidiaries	0	58,000
Current liabilities:
Accounts payable	1,077	3,435
Notes payable to subsidiaries	$ 198,035	$ 134,107

Schedule I - Condensed Financ_4

Schedule I - Condensed Financial Information of Registrant - Condensed Balance Sheets - Parenthetical (Details) - $ / shares	Dec. 31, 2024	Dec. 31, 2023
Condensed Financial Statements, Captions [Line Items]
Common stock, authorized (in shares)	500,000,000	500,000,000
Common stock, par value per share (in usd per share)	$ 1	$ 1
Common stock, issued (in shares)	203,934,578	203,689,090
MDU Resources Group, Inc.
Condensed Financial Statements, Captions [Line Items]
Common stock, authorized (in shares)	500,000,000	500,000,000
Common stock, par value per share (in usd per share)	$ 1	$ 1
Common stock, issued (in shares)	203,934,578	203,689,090

Schedule I - Condensed Financ_5

Schedule I - Condensed Financial Information of Registrant - Condensed Statements of Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Operating activities:
Net cash provided by continuing operations	$ 411,813	$ 305,333	$ 321,615
Net cash provided by discontinued operations	90,505	27,294	188,449
Net cash provided by operating activities	502,318	332,627	510,064
Investing activities:
Investments	(5,155)	(2,423)	(2,571)
Net cash used in continuing operations	(523,827)	(465,129)	(456,929)
Financing activities:
Issuance of short-term borrowings	0	810,000	11,500
Repayment of short-term borrowings	(95,000)	(433,901)	0
Issuance of long-term debt	308,600	594,700	214,969
Repayment of long-term debt	(182,135)	(568,883)	(38,764)
Debt issuance costs	(2,456)	(2,521)	(1,129)
Costs of issuance of common stock	(50)	0	(150)
Dividends paid	(102,939)	(161,316)	(176,915)
Repurchase of common stock	0	(4,811)	(7,399)
Tax withholding on stock-based compensation	(2,623)	(3,040)	(4,904)
Net cash (used in) provided by continuing operations	(76,603)	230,228	(2,792)
Net cash provided by (used in) discontinued operations	116,899	(25,606)	157,965
Net cash provided by financing activities	40,296	204,622	155,173
(Decrease) increase in cash, cash equivalents and restricted cash	(10,071)	(3,542)	26,356
Cash, cash equivalents and restricted cash - beginning of year	60,473
Cash, cash equivalents and restricted cash - end of year	66,904	60,473
MDU Resources Group, Inc.
Operating activities:
Net cash provided by continuing operations	482,195	282,132	253,663
Net cash provided by discontinued operations	(40,007)	(58,591)	(11,464)
Net cash provided by operating activities	442,188	223,541	242,199
Investing activities:
Investments	2,253	7,422	(885)
Repayment (issuance) of notes receivable	58,000	(58,000)	0
Net cash used in continuing operations	(150,747)	(526,578)	(45,885)
Financing activities:
Issuance of short-term borrowings	0	535,000	0
Repayment of short-term borrowings	0	(242,401)	0
Issuance of long-term debt	0	443,000	0
Repayment of long-term debt	(58,000)	(385,000)	0
Debt issuance costs	(401)	(952)	0
Costs of issuance of common stock	(50)	0	(149)
Dividends paid	(102,939)	(161,316)	(176,915)
Repurchase of common stock	0	(2,270)	(3,525)
Tax withholding on stock-based compensation	(1,729)	(1,471)	(2,398)
Net cash (used in) provided by continuing operations	(163,119)	184,590	(182,987)
Net cash provided by (used in) discontinued operations	(132,000)	132,000	0
Net cash provided by financing activities	(295,119)	316,590	(182,987)
(Decrease) increase in cash, cash equivalents and restricted cash	(3,678)	13,553	13,327
Cash, cash equivalents and restricted cash - beginning of year	33,039	19,486	6,159
Cash, cash equivalents and restricted cash - end of year	29,361	33,039	19,486
MDU Resources Group, Inc. | Subsidiaries
Investing activities:
Investments	$ (211,000)	$ (476,000)	$ (45,000)

Schedule I - Condensed Financ_6

Schedule I - Condensed Financial Information of Registrant - Notes to Condensed Financial Statements (Details)			12 Months Ended
	Nov. 01, 2024 USD ($)	Nov. 15, 2023 USD ($)	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	May 31, 2023 USD ($)
Condensed Financial Statements, Captions [Line Items]
Short-term borrowings			$ 0	$ 95,000,000
Long-term debt			2,292,610,000	2,166,223,000
Repayments of long-term debt			182,135,000	568,883,000	$ 38,764,000
Repayment of short-term borrowings			95,000,000	433,901,000	0
Long-term debt, maturities year two			$ 144,700,000
MDU Resources Group, Inc. | Term Loan Agreement
Condensed Financial Statements, Captions [Line Items]
Long-term debt						$ 375,000,000
Repayments of long-term debt	$ 190,000,000	$ 185,000,000
MDU Resources Group, Inc. | Revolving Credit Facility
Condensed Financial Statements, Captions [Line Items]
Ratio of total debt to total capitalization			0.65
Long-term debt						200,000,000
MDU Resources Group, Inc. | Revolving Credit Facility
Condensed Financial Statements, Captions [Line Items]
Short-term borrowings				0		$ 150,000,000
MDU Resources Group, Inc.
Condensed Financial Statements, Captions [Line Items]
Repayments of long-term debt			$ 58,000,000	385,000,000	0
Repayment of short-term borrowings			0	242,401,000	0
Long-term debt, maturities year two			0
Cash dividends paid to parent company by consolidated subsidiaries			$ 418,300,000	$ 165,500,000	$ 242,100,000

Jointly Owned Facilities (Detai

Jointly Owned Facilities (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Jointly Owned Electricity Generation Plant | Big Stone Station
Jointly Owned Utility Plant Interests [Line Items]
Proportionate ownership share	22.70%
Utility plant in service	$ 155,302	$ 159,437
CWIP	318	197
Less accumulated depreciation	55,327	52,264
Utility plant in services net	$ 100,293	107,370
Jointly Owned Electricity Generation Plant | Coyote Station
Jointly Owned Utility Plant Interests [Line Items]
Proportionate ownership share	25%
Utility plant in service	$ 160,343	160,208
CWIP	755	159
Less accumulated depreciation	115,133	113,187
Utility plant in services net	$ 45,965	47,180
Jointly Owned Electricity Generation Plant | Wygen III
Jointly Owned Utility Plant Interests [Line Items]
Proportionate ownership share	25%
Utility plant in service	$ 67,851	66,852
CWIP	97	127
Less accumulated depreciation	15,340	13,728
Utility plant in services net	$ 52,608	53,251
Jointly Owned Electricity Transmission and Distribution System | BSSE
Jointly Owned Utility Plant Interests [Line Items]
Proportionate ownership share	50%
Utility plant in service	$ 111,043	107,260
CWIP	0	0
Less accumulated depreciation	10,359	8,111
Utility plant in services net	$ 100,684	99,149
Jointly Owned Electricity Transmission and Distribution System | JETx
Jointly Owned Utility Plant Interests [Line Items]
Proportionate ownership share	50%
Utility plant in service	$ 0	0
CWIP	6,112	1,372
Less accumulated depreciation	0	0
Utility plant in services net	$ 6,112	$ 1,372