MDU Resources (MDU) 10-Q 7 Nov 24 2024 Q3 Quarterly report Financial data

Cover Page

Cover Page - shares	9 Months Ended
	Sep. 30, 2024	Oct. 31, 2024
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2024
Document Transition Report	false
Entity File Number	1-03480
Entity Registrant Name	MDU RESOURCES GROUP, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	30-1133956
Entity Address, Address Line One	1200 West Century Avenue
Entity Address, Address Line Two	P.O. Box 5650
Entity Address, City or Town	Bismarck
Entity Address, State or Province	ND
Entity Address, Postal Zip Code	58506-5650
City Area Code	701
Local Phone Number	530-1000
Title of 12(b) Security	Common Stock, par value $1.00 per share
Trading Symbol	MDU
Security Exchange Name	NYSE
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		203,888,237
Entity Central Index Key	0000067716
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q3
Amendment Flag	false

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Operating revenues:
Operating revenues:	$ 1,050,516	$ 1,000,795	$ 3,311,886	$ 3,522,020
Operating expenses:
Total operation and maintenance	786,637	738,658	2,191,547	2,304,796
Purchased natural gas sold	53,377	55,967	406,569	542,848
Electric fuel and purchased power	25,210	28,966	87,543	73,755
Depreciation and amortization	56,160	53,146	167,791	158,877
Taxes, other than income	38,328	39,454	141,939	156,587
Total operating expenses	959,712	916,191	2,995,389	3,236,863
Operating income	90,804	84,604	316,497	285,157
Unrealized gain on retained shares in Knife River	0	30,150	0	170,170
Other income	13,838	8,918	42,287	29,251
Interest expense	29,466	32,129	86,780	82,541
Income before income taxes	75,176	91,543	272,004	402,037
Income taxes	13,017	13,325	48,373	92,311
Income from continuing operations	62,159	78,218	223,631	309,726
Discontinued operations, net of tax	2,456	(3,289)	2,319	(65,752)
Net income	$ 64,615	$ 74,929	$ 225,950	$ 243,974
Earnings per share - basic:
Income from continuing operations (in usd per share)	$ 0.31	$ 0.38	$ 1.10	$ 1.52
Discontinued operations, net of tax (in usd per share)	0.01	(0.01)	0.01	(0.32)
Earnings per share - basic (in usd per share)	0.32	0.37	1.11	1.20
Earnings per share - diluted:
Income from continuing operations (in usd per share)	0.31	0.38	1.10	1.52
Discontinued operations, net of tax (in usd per share)	0.01	(0.01)	0.01	(0.32)
Earnings per share - diluted (in usd per share)	$ 0.32	$ 0.37	$ 1.11	$ 1.20
Weighted average common shares outstanding - basic (in shares)	203,888	203,638	203,852	203,633
Weighted average common shares outstanding - diluted (in shares)	204,678	203,886	204,451	203,891
Regulated operation
Operating revenues:
Operating revenues:	$ 286,053	$ 279,534	$ 1,212,615	$ 1,293,959
Operating expenses:
Total operation and maintenance	101,308	99,295	307,697	296,818
Income from continuing operations	21,621	14,628	122,324	100,923
Nonregulated operation
Operating revenues:
Operating revenues:	764,463	721,261	2,099,271	2,228,061
Operating expenses:
Total operation and maintenance	685,329	639,363	1,883,850	2,007,978
Income from continuing operations	$ 40,538	$ 63,590	$ 101,307	$ 208,803

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Statement of Comprehensive Income [Abstract]
Net income	$ 64,615	$ 74,929	$ 225,950	$ 243,974
Other comprehensive income:
Reclassification adjustment for loss on derivative instruments included in net income, net of tax of $17 for the nine months ended 2023	0	0	0	81
Postretirement liability adjustment:
Amortization of postretirement liability losses included in net periodic benefit credit, net of tax of $33 and $98 for the three months ended and $101 and $263 for the nine months ended in 2024 and 2023, respectively	104	(6)	311	481
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 $47 and $(17) for the three months ended and $45 and $(21) for the nine months ended in 2024 and 2023, respectively	177	(66)	170	(80)
Reclassification adjustment for loss on available-for-sale investments included in net income, net of tax of $1 and $3 for the three months ended and $5 and $9 for the nine months ended in 2024 and 2023, respectively	3	10	16	36
Net unrealized gain (loss) on available-for-sale investments	180	(56)	186	(44)
Other comprehensive income (loss)	284	(62)	497	518
Comprehensive income attributable to common stockholders	$ 64,899	$ 74,867	$ 226,447	$ 244,492

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023	Sep. 30, 2023
Current assets:
Cash, cash equivalents and restricted cash	$ 104,016	$ 76,975	$ 32,493
Receivables, net	934,473	942,782	893,019
Current regulatory assets	241,008	172,492	169,248
Inventories	91,889	87,392	80,235
Prepayments and other current assets	96,434	84,082	63,805
Retained shares in Knife River	0	0	276,213
Total current assets	1,467,820	1,363,723	1,515,013
Noncurrent assets:
Property, plant and equipment	7,703,249	7,341,116	7,211,680
Less accumulated depreciation and amortization	2,322,543	2,220,206	2,191,514
Net property, plant and equipment	5,380,706	5,120,910	5,020,166
Goodwill	488,960	488,960	488,960
Other intangible assets, net	466	2,004	2,526
Regulatory assets	343,578	447,099	428,969
Investments	130,602	124,235	139,327
Operating lease right-of-use assets	90,439	74,363	75,729
Other	270,078	211,865	198,459
Total noncurrent assets	6,704,829	6,469,436	6,354,136
Total assets	8,172,649	7,833,159	7,869,149
Current liabilities:
Short-term borrowings	0	95,000	306,400
Long-term debt due within one year	218,777	61,319	61,319
Accounts payable	489,100	475,215	414,479
Taxes payable	61,879	58,110	49,500
Dividends payable	26,024	25,461	25,455
Accrued compensation	97,041	85,512	94,230
Operating lease liabilities due within one year	28,133	22,884	23,112
Regulatory liabilities due within one year	157,068	70,761	45,013
Other accrued liabilities	203,353	181,471	154,147
Total current liabilities	1,281,375	1,075,733	1,173,655
Noncurrent liabilities:
Long-term debt	2,233,520	2,236,904	2,279,828
Deferred income taxes	453,155	458,548	526,654
Asset retirement obligations	397,952	384,371	384,083
Regulatory liabilities	463,790	521,050	495,112
Operating lease liabilities	62,569	51,645	52,908
Other	222,303	199,675	199,475
Total noncurrent liabilities	3,833,289	3,852,193	3,938,060
Commitments and contingencies
Stockholders' equity:
Common stock Authorized - 500,000,000 shares, $1.00 par value Shares issued - 203,888,237 at September 30, 2024, 203,638,373 at September 30, 2023 and 203,689,090 at December 31, 2023	203,888	203,689	203,638
Other paid-in capital	1,470,429	1,466,235	1,462,939
Retained earnings	1,401,555	1,253,693	1,108,616
Accumulated other comprehensive loss	(17,887)	(18,384)	(17,759)
Total stockholders' equity	3,057,985	2,905,233	2,757,434
Total liabilities and stockholders' equity	$ 8,172,649	$ 7,833,159	$ 7,869,149

Consolidated Statements of Equi

Consolidated Statements of Equity - USD ($) $ in Thousands	Total	Discontinued Operations, Disposed of by Means Other than Sale, Spinoff Knife River Corporation	Common Stock	Common Stock Discontinued Operations, Disposed of by Means Other than Sale, Spinoff Knife River Corporation	Other Paid-in Capital	Retained Earnings	Retained Earnings Discontinued Operations, Disposed of by Means Other than Sale, Spinoff Knife River Corporation	Accumulated Other Comprehensive Loss	Accumulated Other Comprehensive Loss Discontinued Operations, Disposed of by Means Other than Sale, Spinoff Knife River Corporation	Treasury Stock	Treasury Stock Discontinued Operations, Disposed of by Means Other than Sale, Spinoff Knife River Corporation
Common stock, beginning balance (in shares) at Dec. 31, 2022			204,162,814
Beginning balance at Dec. 31, 2022	$ 3,587,129		$ 204,163		$ 1,466,037	$ 1,951,138		$ (30,583)		$ (3,626)
Treasury stock, common, beginning balance (in shares) at Dec. 31, 2022										(538,921)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	38,353					38,353
Other comprehensive income (loss)	217							217
Dividends declared on common stock	(45,574)					(45,574)
Stock-based compensation	3,108				3,108
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
Common stock, ending balance (in shares) at Mar. 31, 2023			204,162,814
Ending balance at Mar. 31, 2023	3,575,382		$ 204,163		1,461,294	1,943,917		(30,366)		$ (3,626)
Treasury stock, common, ending balance (in shares) at Mar. 31, 2023										(538,921)
Common stock, beginning balance (in shares) at Dec. 31, 2022			204,162,814
Beginning balance at Dec. 31, 2022	3,587,129		$ 204,163		1,466,037	1,951,138		(30,583)		$ (3,626)
Treasury stock, common, beginning balance (in shares) at Dec. 31, 2022										(538,921)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	243,974
Other comprehensive income (loss)	$ 518
Common stock, ending balance (in shares) at Sep. 30, 2023	203,638,373		203,638,373
Ending balance at Sep. 30, 2023	$ 2,757,434		$ 203,638		1,462,939	1,108,616		(17,759)		$ 0
Treasury stock, common, ending balance (in shares) at Sep. 30, 2023										0
Common stock, beginning balance (in shares) at Mar. 31, 2023			204,162,814
Beginning balance at Mar. 31, 2023	3,575,382		$ 204,163		1,461,294	1,943,917		(30,366)		$ (3,626)
Treasury stock, common, beginning balance (in shares) at Mar. 31, 2023										(538,921)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	130,692					130,692
Other comprehensive income (loss)	363							363
Dividends declared on common stock	(45,158)					(45,158)
Stock-based compensation	$ (927)				(927)
Separation of Knife River (in shares)				538,921							538,921
Separation of Knife River		$ (954,541)		$ (539)			$ (969,934)		$ 12,306		$ 3,626
Issuance of common stock (in shares)	14,480
Costs of issuance of common stock	$ 382		$ 14		368
Common stock, ending balance (in shares) at Jun. 30, 2023			203,638,373
Ending balance at Jun. 30, 2023	2,706,193		$ 203,638		1,460,735	1,059,517		(17,697)		$ 0
Treasury stock, common, ending balance (in shares) at Jun. 30, 2023										0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	74,929					74,929
Other comprehensive income (loss)	(62)							(62)
Dividends declared on common stock	(25,645)					(25,645)
Stock-based compensation	$ 2,204				2,204
Separation of Knife River		$ (185)					$ (185)
Common stock, ending balance (in shares) at Sep. 30, 2023	203,638,373		203,638,373
Ending balance at Sep. 30, 2023	$ 2,757,434		$ 203,638		1,462,939	1,108,616		(17,759)		$ 0
Treasury stock, common, ending balance (in shares) at Sep. 30, 2023										0
Common stock, beginning balance (in shares) at Dec. 31, 2023	203,689,090		203,689,090
Beginning balance at Dec. 31, 2023	$ 2,905,233		$ 203,689		1,466,235	1,253,693		(18,384)		$ 0
Treasury stock, common, beginning balance (in shares) at Dec. 31, 2023										0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	100,898					100,898
Other comprehensive income (loss)	74							74
Dividends declared on common stock	(25,779)					(25,779)
Stock-based compensation	3,173				3,173
Costs of issuance of common stock	(35)				(35)
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)
Common stock, ending balance (in shares) at Mar. 31, 2024			203,888,237
Ending balance at Mar. 31, 2024	$ 2,980,941		$ 203,888		1,466,551	1,328,812		(18,310)		$ 0
Treasury stock, common, ending balance (in shares) at Mar. 31, 2024										0
Common stock, beginning balance (in shares) at Dec. 31, 2023	203,689,090		203,689,090
Beginning balance at Dec. 31, 2023	$ 2,905,233		$ 203,689		1,466,235	1,253,693		(18,384)		$ 0
Treasury stock, common, beginning balance (in shares) at Dec. 31, 2023										0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	225,950
Other comprehensive income (loss)	$ 497
Common stock, ending balance (in shares) at Sep. 30, 2024	203,888,237		203,888,237
Ending balance at Sep. 30, 2024	$ 3,057,985		$ 203,888		1,470,429	1,401,555		(17,887)		$ 0
Treasury stock, common, ending balance (in shares) at Sep. 30, 2024										0
Common stock, beginning balance (in shares) at Mar. 31, 2024			203,888,237
Beginning balance at Mar. 31, 2024	2,980,941		$ 203,888		1,466,551	1,328,812		(18,310)		$ 0
Treasury stock, common, beginning balance (in shares) at Mar. 31, 2024										0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	60,436					60,436
Other comprehensive income (loss)	139							139
Dividends declared on common stock	(25,644)					(25,644)
Stock-based compensation	1,947				1,947
Costs of issuance of common stock	(15)				(15)
Common stock, ending balance (in shares) at Jun. 30, 2024			203,888,237
Ending balance at Jun. 30, 2024	3,017,804		$ 203,888		1,468,483	1,363,604		(18,171)		$ 0
Treasury stock, common, ending balance (in shares) at Jun. 30, 2024										0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	64,615					64,615
Other comprehensive income (loss)	284							284
Dividends declared on common stock	(26,664)					(26,664)
Stock-based compensation	$ 1,946				1,946
Common stock, ending balance (in shares) at Sep. 30, 2024	203,888,237		203,888,237
Ending balance at Sep. 30, 2024	$ 3,057,985		$ 203,888		$ 1,470,429	$ 1,401,555		$ (17,887)		$ 0
Treasury stock, common, ending balance (in shares) at Sep. 30, 2024										0

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Operating activities:
Net income	$ 225,950	$ 243,974
Less: income (loss) from discontinued operations, net of tax	2,319	(65,752)
Income from continuing operations	223,631	309,726
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	167,791	158,877
Deferred income taxes	(12,289)	63,745
Provision for credit losses	4,902	9,769
Amortization of debt issuance costs	1,167	991
Employee stock-based compensation costs	7,067	3,943
Pension and postretirement benefit plan net periodic benefit credit	(2,882)	(4,086)
Unrealized gain on retained shares in Knife River	0	(170,170)
Unrealized gains on investments	(5,813)	(3,501)
Gains on sales of assets	(5,754)	(6,761)
Changes in current assets and liabilities, net of acquisitions:
Receivables	14,510	161,366
Inventories	(6,307)	(19,694)
Other current assets	37,007	(68,161)
Accounts payable	7,176	(132,323)
Other current liabilities	47,057	42,310
Pension and postretirement benefit plan contributions	(2,557)	(7,541)
Other noncurrent changes	(35,238)	(3,362)
Net cash provided by continuing operations	439,468	335,128
Net cash provided by (used in) discontinued operations	2,318	(160,214)
Net cash provided by operating activities	441,786	174,914
Investing activities:
Capital expenditures	(400,989)	(370,585)
Net proceeds from sale or disposition of property	9,590	12,508
Cost of removal, net of salvage value	(6,133)	730
Investments	(3,878)	(3,339)
Proceeds from investment cost basis withdrawal	9,000	0
Net cash used in continuing operations	(392,410)	(360,686)
Net cash used in discontinued operations	0	(55,012)
Net cash used in investing activities	(392,410)	(415,698)
Financing activities:
Issuance of short-term borrowings	0	461,400
Repayment of short-term borrowings	(95,000)	(193,500)
Issuance of long-term debt	302,400	411,900
Repayment of long-term debt	(147,731)	(434,994)
Debt issuance costs	(2,416)	(1,844)
Costs of issuance of common stock	(50)	0
Dividends paid	(76,915)	(135,861)
Repurchase of common stock	0	(4,811)
Tax withholding on stock-based compensation	(2,623)	(3,040)
Net cash (used in) provided by continuing operations	(22,335)	99,250
Net cash provided by discontinued operations	0	93,509
Net cash (used in) provided by financing activities	(22,335)	192,759
Increase (decrease) in cash, cash equivalents and restricted cash	27,041	(48,025)
Cash, cash equivalents and restricted cash - beginning of year	76,975	80,518
Cash, cash equivalents and restricted cash - end of period	$ 104,016	$ 32,493

Consolidated Statements of Co_2

Consolidated Statements of Comprehensive Income (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Statement of Comprehensive Income [Abstract]
Reclassification adjustment for loss on derivative instruments included in net income, tax				$ 17
Amortization of postretirement liability losses included in net periodic benefit credit, tax	$ 33	$ 98	$ 101	263
Net unrealized gain (loss) on available-for-sale investments arising during the period, tax	47	(17)	45	(21)
Reclassification adjustment for loss on available-for-sale investments included in net income, tax	$ 1	$ 3	$ 5	$ 9

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2024	Dec. 31, 2023	Sep. 30, 2023
Statement of Financial Position [Abstract]
Common stock, authorized (in shares)	500,000,000	500,000,000	500,000,000
Common stock, par value per share (in usd per share)	$ 1	$ 1	$ 1
Common stock, issued (in shares)	203,888,237	203,689,090	203,638,373

Basis of presentation

Basis of presentation	9 Months Ended
	Sep. 30, 2024
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of presentation	Basis of presentation The accompanying consolidated interim financial statements were prepared in accordance with GAAP for interim financial information and with the instructions to Form 10-Q and Rule 10-01 of Regulation S-X. Interim financial statements do not include all disclosures provided in annual financial statements and, accordingly, these financial statements should be read in conjunction with those appearing in the 2023 Annual Report. The information is unaudited but includes all adjustments that are, in the opinion of management, necessary for a fair presentation of the accompanying consolidated interim financial statements and are of a normal recurring nature. Depreciation and amortization expense is reported separately on the Consolidated Statements of Income and therefore is excluded from the other line items within operating expenses. On May 31, 2023, the Company completed the separation of Knife River, formerly the construction materials and contracting segment, which resulted in two independent, publicly-traded companies, MDU Resources Group, Inc. and Knife River. 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 Company's consolidated financial statements and accompanying notes for the current and prior periods present the results of operations of Knife River as discontinued operations, other than certain corporate overhead costs of the Company historically allocated to Knife River, which are reflected in Other. Also included in Discontinued operations, net of tax 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 separation. 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. 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 distribution is expected to be tax-free to the Company's stockholders for U.S. federal income tax purposes, except for cash received in lieu of fractional shares. As of September 30, 2024, the spinoff of Everus did not meet the criteria for discontinued operations and its results are included in continuing operations in the Company's Consolidated Financial Statements.

New accounting standards

New accounting standards	9 Months Ended
	Sep. 30, 2024
Accounting Standards Update and Change in Accounting Principle [Abstract]
New accounting standards	New accounting standards The following table provides a brief description of the accounting pronouncements applicable to the Company and the potential impact on its Consolidated 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 was beyond the 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 does not expect the guidance to have a material impact on its results of operations, financial position, cash flows or disclosures. Recently issued accounting standards not yet adopted ASU 2023-05 Business Combinations - Joint Venture Formations - Recognition and Initial Measurement In August 2023, the FASB issued guidance on accounting for contributions made to a joint venture, upon formation, in a joint venture's separate financial statement in order to provide decision-useful information to investors and other allocators of capital (collectively investors) in a joint venture's financial statements and reduce diversity in practice. The new basis of accounting will require that a joint venture, upon formation, will recognize and initially measure its assets and liabilities at fair value (with the exceptions to fair value measurement that are consistent with the business combinations guidance). A joint venture that was formed before January 1, 2025 may elect to apply the guidance retrospectively if it has sufficient information. Effective prospectively for all joint venture formations with a formation date on or after January 1, 2025. The Company is currently evaluating the impact the guidance will have on its interim and annual disclosures for the year ended December 31, 2025. 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. Effective for fiscal year December 31, 2024 and interim periods beginning January 1, 2025, with prior periods disclosed in the period of adoption. The Company is currently evaluating the impact the guidance will have on its disclosures for the year ended December 31, 2024 and future interim periods. ASU 2023-09 Income Taxes - Improvements to Income Tax Disclosures an Amendment, 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. December 31, 2025 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 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.

Discontinued operations

Discontinued operations	9 Months Ended
	Sep. 30, 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 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. As a result of the separation, the historical results of operations are shown in discontinued operations, net of tax, other than allocated general corporate overhead costs of the Company, which do not meet the criteria for income (loss) from discontinued operations. 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, 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 Company provided to Knife River and Knife River provided to the Company transition services in accordance with the TSA entered into on May 31, 2023. For the three and nine months ended September 30, 2024, the Company received $39,000 and $1.5 million, respectively, and paid $15,000 and $155,000, respectively, for these related activities. For the three and nine months ended September 30, 2023, the Company received $1.3 million and $1.9 million, respectively, and paid $407,000 and $684,000, respectively, for these related activities. The majority of the transition services were to be provided for a period of one year, however, no longer than two years after the separation. Separation related costs of $204,000 and $342,000, net of tax, were incurred during the three and nine months ended September 30, 2024, respectively. Separation related costs of $1.0 million and $47.1 million, net of tax, were incurred during the three and nine months ended September 30, 2023, respectively. Separation costs incurred are presented in Discontinued operations, net of tax in the Consolidated Statements of Income. These charges primarily relate to transaction and third-party support costs, one-time business separation fees and related tax charges. The Company had no assets or liabilities related to the discontinued operations of Knife River on its balance sheet as of September 30, 2024 and 2023 and December 31, 2023. The reconciliation of the major classes of income and expense constituting pretax loss from discontinued operations to the after-tax loss from discontinued operations on the Consolidated Statements of Income were as follows: Three Months Ended Nine Months Ended September 30, September 30, 2024 2023 2024 2023 (In thousands) Operating revenues $ — $ — $ — $ 735,259 Operating expenses 270 1,447 431 769,407 Operating (loss) income (270) (1,447) (431) (34,148) Other income — — — 2,382 Interest expense — (66) — 37,545 Loss from discontinued operations before income taxes (270) (1,381) (431) (69,311) Income tax (benefit) expense (2,726) 1,908 (2,750) (3,559) Discontinued operations, net of tax $ 2,456 $ (3,289) $ 2,319 $ (65,752)

Seasonality of operations

Seasonality of operations	9 Months Ended
	Sep. 30, 2024
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Seasonality of operations	Seasonality of operations Some of the Company's operations are highly seasonal and revenues from, and certain expenses for, such operations may fluctuate significantly among quarterly periods. Accordingly, the interim results for particular businesses, and for the Company as a whole, may not be indicative of results for the full fiscal year.

Receivables and allowance for e

Receivables and allowance for expected credit losses	9 Months Ended
	Sep. 30, 2024
Credit Loss [Abstract]
Receivables and allowance for expected credit loss	Receivables and allowance for expected credit losses Receivables consist primarily of trade and contracting services 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 $79.9 million, $51.1 million and $45.7 million at September 30, 2024 and 2023, and December 31, 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 Construction Total (In thousands) At December 31, 2023 $ 414 $ 1,189 $ — $ 7,967 $ 9,570 Current expected credit loss provision 782 1,916 — (411) 2,287 Less write-offs charged against the allowance 659 1,455 — 48 2,162 Credit loss recoveries collected 147 314 — — 461 At March 31, 2024 $ 684 $ 1,964 $ — $ 7,508 $ 10,156 Current expected credit loss provision 190 214 — 277 681 Less write-offs charged against the allowance 463 969 — 541 1,973 Credit loss recoveries collected 80 196 — 13 289 At June 30, 2024 $ 491 $ 1,405 $ — $ 7,257 $ 9,153 Current expected credit loss provision 520 1,330 — 84 1,934 Less write-offs charged against the allowance 594 2,121 — 84 2,799 Credit loss recoveries collected 86 255 — 43 384 At September 30, 2024 $ 503 $ 869 $ — $ 7,300 $ 8,672 Electric Natural gas Pipeline Construction Total (In thousands) At December 31, 2022 $ 375 $ 1,615 $ 2 $ 2,162 $ 4,154 Current expected credit loss provision 615 2,324 — 826 3,765 Less write-offs charged against the allowance 667 1,225 — 51 1,943 Credit loss recoveries collected 145 229 — 1 375 At March 31, 2023 $ 468 $ 2,943 $ 2 $ 2,938 $ 6,351 Current expected credit loss provision 182 90 — 1,825 2,097 Less write-offs charged against the allowance 316 1,454 — 103 1,873 Credit loss recoveries collected 79 161 — 58 298 At June 30, 2023 $ 413 $ 1,740 $ 2 $ 4,718 $ 6,873 Current expected credit loss provision 513 1,661 — 1,733 3,907 Less write-offs charged against the allowance 572 2,758 — 27 3,357 Credit loss recoveries collected 75 233 — — 308 At September 30, 2023 $ 429 $ 876 $ 2 $ 6,424 $ 7,731

Inventories and natural gas in

Inventories and natural gas in storage	9 Months Ended
	Sep. 30, 2024
Inventory Disclosure [Abstract]
Inventories and natural gas in storage	Inventories and natural gas in storage Natural gas in storage for the Company's regulated operations is generally valued at lower of cost or market using the last-in, first-out method or lower of cost or net realizable value using the average cost or first-in, first-out method. The majority of all other inventories are valued at the lower of cost or net realizable value using the average cost method. The portion of the cost of natural gas in storage expected to be used within 12 months was included in inventories. Inventories on the Consolidated Balance Sheets were as follows: September 30, 2024 September 30, 2023 December 31, 2023 (In thousands) Natural gas in storage (current) $ 40,770 $ 29,821 $ 39,377 Merchandise for resale 38,311 36,815 34,955 Materials and supplies 6,264 7,824 5,460 Other 6,544 5,775 7,600 Total $ 91,889 $ 80,235 $ 87,392

Earnings per share

Earnings per share	9 Months Ended
	Sep. 30, 2024
Earnings Per Share [Abstract]
Earnings per share	Earnings per share Basic earnings per share is computed by dividing net income by the weighted average number of shares of common stock outstanding during the applicable period. Diluted earnings per share is computed by dividing net income by the total of the weighted average number of shares of common stock outstanding during the applicable period, plus the effect of non-vested performance share awards and restricted stock units. Net income was the same for both the basic and diluted earnings per share calculations. A reconciliation of the weighted average common shares outstanding used in the basic and diluted earnings per share calculations follows: Three Months Ended Nine Months Ended September 30, September 30, 2024 2023 2024 2023 (In thousands, except per share amounts) Weighted average common shares outstanding - basic 203,888 203,638 203,852 203,633 Effect of dilutive performance share awards and restricted stock units 790 248 599 258 Weighted average common shares outstanding - diluted 204,678 203,886 204,451 203,891 Earnings per share - basic: Income from continuing operations $ .31 $ .38 $ 1.10 $ 1.52 Discontinued operations, net of tax .01 (.01) .01 (.32) Earnings per share - basic $ .32 $ .37 $ 1.11 $ 1.20 Earnings per share - diluted: Income from continuing operations $ .31 $ .38 $ 1.10 $ 1.52 Discontinued operations, net of tax .01 (.01) .01 (.32) Earnings per share - diluted $ .32 $ .37 $ 1.11 $ 1.20 Shares excluded from the calculation of diluted earnings per share — — — — Dividends declared per common share $ .1300 $ .1250 $ .3800 $ .5700

Revenue from contracts with cus

Revenue from contracts with customers	9 Months Ended
	Sep. 30, 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. The Company recognizes revenue from the sale of emissions allowances allocated under the environmental programs in certain states. The Company has the right to payment when the allowances are sold at auction. Revenue is recognized on a point in time basis within the quarter that the auction is held. The revenues associated with the sale of these allowances are deferred as a component of the respective jurisdiction’s regulatory asset or liability for environmental compliance. For more information on the Company’s regulatory assets and liabilities, see Note 10. Changes in cost estimates on certain contracts may result in the issuance of change orders, which can be approved or unapproved by the customer, or the assertion of contract claims. The Company recognizes amounts associated with change orders and claims as revenue if it is probable that the contract price will be adjusted and the amount of any such adjustment can be reasonably estimated. Change orders and claims are negotiated in the normal course of business and represent management’s estimates of additional contract revenues that have been earned and are probable of collection. The Company received notification in 2023 from a customer on a large project with a contract that was billed on a time and materials basis with no stated maximum price, that it is withholding payment of approximately $31.2 million on remaining outstanding billings, including retention. The Company believes it has substantial defenses against these claims based upon the terms of the contract and the Company's belief that it has fully performed under the terms of the contract. The Company believes collection of the remaining outstanding billings, including retention is probable and, as a result, the Company has recognized the revenue from this project in its results. However, there is uncertainty surrounding this matter, including the potential long-term nature of dispute resolution, the Company filing a lien on the property and the broad range of possible consideration amounts as a result of negotiations and potential litigation to resolve the dispute. Disaggregation In the following tables, revenue is disaggregated by the type of customer or service provided. The Company believes this level of disaggregation best depicts how the nature, amount, timing and uncertainty of revenue and cash flows are affected by economic factors. The table also includes a reconciliation of the disaggregated revenue by reportable segments. For more information on the Company's business segments, see Note 15. Three Months Ended September 30, 2024 Electric Natural gas Pipeline Construction Other Total (In thousands) Residential utility sales $ 37,076 $ 61,928 $ — $ — $ — $ 99,004 Commercial utility sales 46,648 37,687 — — — 84,335 Industrial utility sales 9,702 6,869 — — — 16,571 Other utility sales 2,045 — — — — 2,045 Natural gas transportation — 15,279 41,936 — — 57,215 Natural gas storage — — 6,053 — — 6,053 Electrical & mechanical specialty contracting — — — 534,613 — 534,613 Transmission & distribution specialty contracting — — — 216,062 — 216,062 Other 16,182 9,736 3,537 169 1,433 31,057 Intersegment eliminations (96) (104) (3,931) — (1,432) (5,563) Revenues from contracts with customers 111,557 131,395 47,595 750,844 1 1,041,392 Other revenues (3,173) 2,122 33 10,142 — 9,124 Total external operating revenues $ 108,384 $ 133,517 $ 47,628 $ 760,986 $ 1 $ 1,050,516 Three Months Ended September 30, 2023 Electric Natural gas Pipeline Construction Other Total (In thousands) Residential utility sales $ 34,303 $ 68,733 $ — $ — $ — $ 103,036 Commercial utility sales 49,754 40,360 — — — 90,114 Industrial utility sales 10,747 7,272 — — — 18,019 Other utility sales 1,865 — — — — 1,865 Natural gas transportation — 13,050 35,338 — — 48,388 Natural gas storage — — 4,808 — — 4,808 Electrical & mechanical specialty contracting — — — 514,378 — 514,378 Transmission & distribution specialty contracting — — — 192,056 — 192,056 Other 14,701 3,881 3,916 (89) 1,689 24,098 Intersegment eliminations (27) (69) (3,701) — (1,689) (5,486) Revenues from contracts with customers 111,343 133,227 40,361 706,345 — 991,276 Other revenues (3,254) 1,669 43 11,061 — 9,519 Total external operating revenues $ 108,089 $ 134,896 $ 40,404 $ 717,406 $ — $ 1,000,795 Nine Months Ended September 30, 2024 Electric Natural gas Pipeline Construction Other Total (In thousands) Residential utility sales $ 107,735 $ 431,721 $ — $ — $ — $ 539,456 Commercial utility sales 129,783 264,091 — — — 393,874 Industrial utility sales 32,809 30,716 — — — 63,525 Other utility sales 6,046 — — — — 6,046 Natural gas transportation — 43,194 128,979 — — 172,173 Natural gas storage — — 16,766 — — 16,766 Electrical & mechanical specialty contracting — — — 1,476,006 — 1,476,006 Transmission & distribution specialty contracting — — — 583,803 — 583,803 Other 44,998 18,705 9,903 260 4,283 78,149 Intersegment eliminations (188) (209) (43,296) (336) (4,265) (48,294) Revenues from contracts with customers 321,183 788,218 112,352 2,059,733 18 3,281,504 Revenues out of scope (5,915) 6,200 119 29,978 — 30,382 Total external operating revenues $ 315,268 $ 794,418 $ 112,471 $ 2,089,711 $ 18 $ 3,311,886 Nine Months Ended September 30, 2023 Electric Natural gas Pipeline Construction Other Total (In thousands) Residential utility sales $ 102,953 $ 517,351 $ — $ — $ — $ 620,304 Commercial utility sales 124,363 316,483 — — — 440,846 Industrial utility sales 31,880 33,293 — — — 65,173 Other utility sales 5,349 — — — — 5,349 Natural gas transportation — 38,225 104,716 — — 142,941 Natural gas storage — — 12,427 — — 12,427 Electrical & mechanical specialty contracting — — — 1,672,948 — 1,672,948 Transmission & distribution specialty contracting — — — 511,563 — 511,563 Other 38,111 11,874 9,713 121 6,412 66,231 Intersegment eliminations (82) (208) (37,889) — (6,412) (44,591) Revenues from contracts with customers 302,574 917,018 88,967 2,184,632 — 3,493,191 Revenues out of scope (7,799) 2,469 119 34,040 — 28,829 Total external operating revenues $ 294,775 $ 919,487 $ 89,086 $ 2,218,672 $ — $ 3,522,020 Contract balances The timing of revenue recognition may differ from the timing of invoicing to customers. The timing of invoicing to customers does not necessarily correlate with the timing of revenues being recognized under the cost-to-cost method of accounting. Contracts from contracting services are billed as work progresses in accordance with agreed upon contractual terms. Generally, billing to the customer occurs contemporaneous to revenue recognition. A variance in timing of the billings may result in a contract asset or a contract liability. A contract asset occurs when revenues are recognized under the cost-to-cost measure of progress, which exceeds amounts billed on uncompleted contracts. Such amounts will be billed as standard contract terms allow, usually based on various measures of performance or achievement. A contract liability occurs when there are billings in excess of revenues recognized under the cost-to-cost measure of progress on uncompleted contracts. Contract liabilities decrease as revenue is recognized from the satisfaction of the related performance obligation. The changes in contract assets and liabilities were as follows: September 30, 2024 December 31, 2023 Change Location on Consolidated Balance Sheets (In thousands) Contract assets $ 174,782 $ 158,861 $ 15,921 Receivables, net Contract liabilities - current (226,754) (202,144) (24,610) Accounts payable Contract liabilities - noncurrent (2,114) (291) (1,823) Noncurrent liabilities - other Net contract liabilities $ (54,086) $ (43,574) $ (10,512) The Company recognized $47.4 million and $169.0 million in revenue for the three and nine months ended September 30, 2024, respectively, which was previously included in contract liabilities at December 31, 2023. The Company recognized $6.3 million and $164.3 million in revenue for the three and nine months ended September 30, 2023, respectively, which was previously included in contract liabilities at December 31, 2022. The Company recognized a net increase in revenues of $25.8 million and $71.8 million for the three and nine months ended September 30, 2024, respectively, from performance obligations satisfied in prior periods. The Company recognized a net increase in revenues of $20.2 million and $41.7 million for the three and nine months ended September 30, 2023, respectively, from performance obligations satisfied in prior periods. Remaining performance obligations The remaining performance obligations, also referred to as backlog, at the construction services segment include unrecognized revenues that the Company reasonably expects to be realized. These unrecognized revenues can include: projects that have a written award, a letter of intent, a notice to proceed, an agreed upon work order to perform work on mutually accepted terms and conditions and change orders or claims to the extent management believes additional contract revenues will be earned and are deemed probable of collection. Excluded from remaining performance obligations are potential orders under master service agreements. The majority of the Company's construction contracts have an original duration of less than two years. The remaining performance obligations at the pipeline segment include firm transportation and storage contracts with fixed pricing and fixed volumes. The Company has applied the practical expedient that does not require additional disclosures for contracts with an original duration of less than 12 months, to certain firm transportation, storage and non-regulated contracts. The Company's firm transportation and storage contracts included in the remaining performance obligations have weighted average remaining durations of less than five years and two years, respectively. At September 30, 2024, the Company's remaining performance obligations were $3.5 billion. The Company expects to recognize the following revenue amounts in future periods related to these remaining performance obligations: $2.3 billion within the next 12 months or less; $681.1 million within the next 13 to 24 months; and $551.1 million in 25 months or more.

Leases

Leases	9 Months Ended
	Sep. 30, 2024
Leases [Abstract]
Leases	Leases The Company's leases primarily include operating leases for equipment, buildings, easements and vehicles. The Company leases certain equipment to third parties through its utility and construction services segments, which are considered short-term operating leases with terms of less than 12 months. The Company recognized revenue from operating leases of $10.3 million and $30.3 million for the three and nine months ended September 30, 2024, respectively. The Company recognized revenue from operating leases of $11.2 million and $34.5 million for the three and nine months ended September 30, 2023, respectively. At September 30, 2024, the Company had $8.6 million of lease receivables with a majority due within 12 months.

Regulatory assets and liabiliti

Regulatory assets and liabilities	9 Months Ended
	Sep. 30, 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: Estimated Recovery or Refund Period as of September 30, 2024 * September 30, 2024 September 30, 2023 December 31, 2023 (In thousands) Regulatory assets: Current: Natural gas costs recoverable through rate adjustments Up to 1 year $ 111,946 $ 107,101 $ 98,844 Environmental compliance programs Up to 1 year 80,198 3,972 5,525 Conservation programs Up to 1 year 19,059 14,411 14,425 Demand cost deferral Up to 1 year 13,898 13,254 5,207 Electric fuel and purchased power deferral Up to 1 year 4,497 17,775 33,918 Cost recovery mechanisms Up to 1 year 4,332 9,461 9,153 Other Up to 1 year 7,078 3,274 5,420 241,008 169,248 172,492 Noncurrent: Pension and postretirement benefits ** 142,511 144,448 142,511 Cost recovery mechanisms Up to 25 years 82,907 68,539 85,944 Plant costs/asset retirement obligations Over plant lives 45,249 43,520 46,009 Manufactured gas plant site remediation - 25,789 24,577 26,127 Taxes recoverable from customers Over plant lives 12,316 12,266 12,249 Natural gas costs recoverable through rate adjustments Up to 2 years 11,707 64,914 55,493 Electric fuel and purchased power deferral Up to 2 years 8,335 — — Environmental compliance programs - 2,858 36,605 66,806 Long-term debt refinancing costs Up to 36 years 2,159 2,747 2,600 Plant to be retired - 22 19,947 772 Other Up to 15 years 9,725 11,406 8,588 343,578 428,969 447,099 Total regulatory assets $ 584,586 $ 598,217 $ 619,591 Regulatory liabilities: Current: Environmental compliance programs Up to 1 year $ 77,392 $ — $ — Natural gas costs refundable through rate adjustments Up to 1 year 54,197 20,445 43,161 Provision for rate refund Up to 1 year 8,868 2,717 6,866 Margin sharing Up to 1 year 3,945 2,697 5,243 Conservation programs Up to 1 year 2,662 1,976 2,130 Cost recovery mechanisms Up to 1 year 2,634 5,754 6,284 Taxes refundable to customers Up to 1 year 2,195 1,513 2,149 Other Up to 1 year 5,175 9,911 4,928 157,068 45,013 70,761 Noncurrent: Plant removal and decommissioning costs Over plant lives 224,839 220,499 220,147 Taxes refundable to customers Over plant lives 184,715 194,804 193,578 Cost recovery mechanisms Up to 18 years 28,397 20,012 21,791 Accumulated deferred investment tax credit Over plant lives 17,679 14,800 15,740 Pension and postretirement benefits ** 6,043 7,120 6,044 Environmental compliance programs - — 36,126 61,941 Other Up to 14 years 2,117 1,751 1,809 463,790 495,112 521,050 Total regulatory liabilities $ 620,858 $ 540,125 $ 591,811 Net regulatory position $ (36,272) $ 58,092 $ 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. At September 30, 2024 and 2023, and December 31, 2023, approximately $178.8 million, $211.8 million and $194.3 million, respectively, of regulatory assets were not earning a rate of return; however, these regulatory assets 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. 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	9 Months Ended
	Sep. 30, 2024
Accounting Policies [Abstract]
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 10.

Fair value measurements

Fair value measurements	9 Months Ended
	Sep. 30, 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 $63.7 million, $62.7 million and $66.2 million, at September 30, 2024 and 2023, and December 31, 2023, respectively, are classified as Investments on the Consolidated Balance Sheets. The net unrealized gain on these investments was $2.6 million and $5.8 million for the three and nine months ended September 30, 2024, respectively. The net unrealized loss on these investments was $1.4 million for the three months ended and an unrealized gain of $3.5 million for the nine months ended September 30, 2023. 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: September 30, 2024 Cost Gross Gross Fair Value (In thousands) Mortgage-backed securities $ 8,104 $ 41 $ 312 $ 7,833 U.S. Treasury securities 3,897 74 — 3,971 Total $ 12,001 $ 115 $ 312 $ 11,804 September 30, 2023 Cost Gross Gross Fair Value (In thousands) Mortgage-backed securities $ 8,386 $ — $ 750 $ 7,636 U.S. Treasury securities 3,307 11 23 3,295 Total $ 11,693 $ 11 $ 773 $ 10,931 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 On May 31, 2023, the Company completed the Knife River separation and 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 Company did not retain a controlling interest in Knife River and therefore the fair value of its retained shares and subsequent fair value changes are included in assets of and results from continuing operations, respectively. At September 30, 2023, the fair value of the Company's retained shares in Knife River common stock of $276.2 million was reflected in Retained shares in Knife River on the Consolidated Balance Sheet and was remeasured at fair value based on Knife River's closing stock price on September 30, 2023, with an unrealized gain of $30.2 million and $170.2 million for the three and nine months ended September 30, 2023, respectively, which is recorded in Unrealized gain on retained shares in Knife River on the Consolidated Statements of Income. The Company's assets measured at fair value on a recurring basis were as follows: Fair Value Measurements at September 30, 2024, Using Quoted Prices in Significant Significant Balance at September 30, 2024 (In thousands) Assets: Money market funds $ — $ 11,033 $ — $ 11,033 Insurance contracts* — 63,658 — 63,658 Available-for-sale securities: Mortgage-backed securities — 7,833 — 7,833 U.S. Treasury securities — 3,971 — 3,971 Total assets measured at fair value $ — $ 86,495 $ — $ 86,495 * The insurance contracts invest approximately 55 percent in fixed-income investments, 18 percent in common stock of large-cap companies, 10 percent in target date investments, 8 percent in common stock of mid-cap companies, 4 percent in common stock of small-cap companies, 4 percent in cash equivalents, and 1 percent in international investments. Fair Value Measurements at September 30, 2023, Using Quoted Prices in Significant Significant Balance at September 30, 2023 (In thousands) Assets: Retained shares in Knife River $ 276,213 $ — $ — $ 276,213 Money market funds — 25,818 — 25,818 Insurance contracts* — 62,736 — 62,736 Available-for-sale securities: Mortgage-backed securities — 7,637 — 7,637 U.S. Treasury securities — 3,295 — 3,295 Total assets measured at fair value $ 276,213 $ 99,486 $ — $ 375,699 * The insurance contracts invest approximately 50 percent in fixed-income investments, 19 percent in common stock of large-cap companies, 10 percent in target date investments, 10 percent in common stock of mid-cap companies, 6 percent in common stock of small-cap companies, 3 percent in cash equivalents, 1 percent in international investments, and 1 percent in high-yield investments. Fair Value Measurements at December 31, 2023, Using Quoted Prices in Significant Significant Balance at December 31, 2023 (In thousands) Assets: Money market funds $ — $ 6,409 $ — $ 6,409 Insurance contracts* — 66,283 — 66,283 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 $ — $ 84,014 $ — $ 84,014 * 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 was as follows: September 30, 2024 September 30, 2023 December 31, 2023 (In thousands) Carrying amount $ 2,452,297 $ 2,341,147 $ 2,298,223 Fair value $ 2,207,359 $ 1,960,926 $ 2,046,039 The carrying amounts of the Company's remaining financial instruments included in current assets and current liabilities approximate their fair values.

Debt

Debt	9 Months Ended
	Sep. 30, 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 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 September 30, 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. 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 $150.0 million 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 $125.0 million term loan agreement. Long-term debt 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. 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. WBI Energy Transmission 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. Montana-Dakota 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 total capitalization to be greater than 65 percent. The covenants also include certain restrictions on the sale of certain assets, loans and investments. Long-term Debt Outstanding Long-term debt outstanding was as follows: Weighted Average Interest Rate at September 30, 2024 September 30, 2024 September 30, 2023 December 31, 2023 (In thousands) Senior Notes due on dates ranging from August 23, 2025 to June 15, 2062 4.57 % $ 1,947,000 $ 1,757,000 $ 1,882,000 Term Loan Agreements due on dates ranging from May 31, 2025 to April 1, 2039 5.67 % 255,600 381,300 196,300 Credit agreements due on June 20, 2029 6.57 % 163,500 38,900 46,100 Commercial paper supported by revolving credit agreement 5.31 % 57,800 97,700 144,200 Medium-Term Notes due on dates ranging from September 15, 2027 to March 16, 2029 7.32 % 35,000 35,000 35,000 Other notes due on dates ranging from May 31, 2028 to November 30, 2038 6.00 % 350 37,884 980 Less unamortized debt issuance costs 6,953 6,637 6,357 Total long-term debt 2,452,297 2,341,147 2,298,223 Less current maturities 218,777 61,319 61,319 Net long-term debt $ 2,233,520 $ 2,279,828 $ 2,236,904 Schedule of Debt Maturities Long-term debt maturities, which excludes unamortized debt issuance costs and discount, at September 30, 2024, were as follows: Remainder of 2024 2025 2026 2027 2028 Thereafter (In thousands) Long-term debt maturities $ — $ 351,700 $ 144,700 $ 24,700 $ 137,500 $ 1,800,650

Cash flow information

Cash flow information	9 Months Ended
	Sep. 30, 2024
Supplemental Cash Flow Information [Abstract]
Cash flow information	Cash flow information Cash expenditures for interest and income taxes were as follows: Nine Months Ended September 30, 2024 2023 (In thousands) Interest, net* $ 74,504 $ 84,352 Income taxes paid, net** $ 53,553 $ 40,290 * AFUDC - borrowed was $8.4 million and $7.4 million for the nine months ended September 30, 2024 and 2023, respectively. Interest, net also includes interest classified as discontinued operations in 2023. ** Income taxes paid, including discontinued operations, was $39.4 million for the nine months ended September 30, 2023. Noncash investing and financing transactions were as follows: September 30, 2024 September 30, 2023 December 31, 2023 (In thousands) Right-of-use assets obtained in exchange for new operating lease liabilities $ 39,558 $ 36,307 $ 46,181 Property, plant and equipment additions in accounts payable $ 49,686 $ 37,598 $ 46,622

Business segment data

Business segment data	9 Months Ended
	Sep. 30, 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 units due to differences in products, services and regulation. The internal reporting of these operating segments is defined based on the reporting and review process used by the Company's chief executive officer. The Company's operations are located within the United States. 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 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 construction services segment provides a full spectrum of construction services through its electrical and mechanical and transmission and distribution specialty contracting services across the United States. These specialty contracting services are provided to utilities, manufacturing, transportation, commercial, industrial, institutional, renewable and governmental customers. Its electrical and mechanical contracting services include construction and maintenance of electrical and communication wiring and infrastructure, fire suppression systems, and mechanical piping and services. Its transmission and distribution contracting services include construction and maintenance of overhead and underground electrical, gas and communication infrastructure, as well as manufacturing and supplying transmission and distribution line construction equipment and tools. 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 real and 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 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, Fidelity and the refining business which do not meet the criteria for income (loss) from discontinued operations. Discontinued operations includes Knife River's operations, associated separation costs and interest on debt facilities repaid in connection with the Knife River separation. 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 of the Notes to Consolidated Financial Statements in the 2023 Annual Report. Information on the Company's segments was as follows: Three Months Ended Nine Months Ended September 30, September 30, 2024 2023 2024 2023 (In thousands) External operating revenues: Regulated operations: Electric $ 108,384 $ 108,089 $ 315,268 $ 294,775 Natural gas distribution 133,517 134,896 794,418 919,487 Pipeline 44,152 36,549 102,929 79,697 286,053 279,534 1,212,615 1,293,959 Non-regulated operations: Pipeline 3,476 3,855 9,542 9,389 Construction services 760,986 717,406 2,089,711 2,218,672 Other 1 — 18 — 764,463 721,261 2,099,271 2,228,061 Total external operating revenues $ 1,050,516 $ 1,000,795 $ 3,311,886 $ 3,522,020 Intersegment operating revenues: Regulated operations: Electric $ 96 $ 27 $ 188 $ 82 Natural gas distribution 104 69 209 208 Pipeline 3,904 3,666 43,033 37,624 4,104 3,762 43,430 37,914 Non-regulated operations: Pipeline 27 35 263 265 Construction services — — 336 — Other 1,432 1,689 4,265 6,412 1,459 1,724 4,864 6,677 Total intersegment operating revenues $ 5,563 $ 5,486 $ 48,294 $ 44,591 Operating income (loss): Electric $ 32,079 $ 28,718 $ 73,498 $ 71,372 Natural gas distribution (14,695) (15,258) 44,747 45,674 Pipeline 22,179 17,767 68,101 44,693 Construction services 53,709 50,091 143,902 139,619 Other (2,468) 3,286 (13,751) (16,201) Total operating income $ 90,804 $ 84,604 $ 316,497 $ 285,157 Income (loss) from continuing operations: Regulated operations: Electric $ 24,292 $ 20,942 $ 57,689 $ 53,887 Natural gas distribution (17,481) (17,764) 17,581 18,007 Pipeline 14,810 11,450 47,054 29,029 21,621 14,628 122,324 100,923 Non-regulated operations: Pipeline 374 508 447 337 Construction services 41,767 35,975 108,953 105,951 Other (1,603) 27,107 (8,093) 102,515 40,538 63,590 101,307 208,803 Income from continuing operations 62,159 78,218 223,631 309,726 Discontinued operations, net of tax 2,456 (3,289) 2,319 (65,752) Net income $ 64,615 $ 74,929 $ 225,950 $ 243,974 A reconciliation of reportable segment operating revenues to consolidated operating revenues is as follows: Three Months Ended Nine Months Ended September 30, September 30, 2024 2023 2024 2023 (In thousands) Operating revenues reconciliation: Total reportable segment operating revenues $ 1,054,646 $ 1,004,592 $ 3,355,897 $ 3,560,199 Other revenue 1,433 1,689 4,283 6,412 Elimination of intersegment operating revenues (5,563) (5,486) (48,294) (44,591) Total consolidated operating revenues $ 1,050,516 $ 1,000,795 $ 3,311,886 $ 3,522,020

Employee benefit plans

Employee benefit plans	9 Months Ended
	Sep. 30, 2024
Retirement Benefits [Abstract]
Employee benefit plans	Employee benefit plans Pension and other postretirement plans The Company has noncontributory qualified defined benefit pension plans and other postretirement benefit plans for certain eligible employees. Components of net periodic benefit cost (credit) for the Company's pension benefit plans were as follows: Three Months Ended Nine Months Ended September 30, September 30, 2024 2023 2024 2023 (In thousands) Components of net periodic benefit cost (credit): Interest cost $ 3,200 $ 3,380 $ 9,600 $ 10,140 Expected return on assets (4,028) (4,299) (12,084) (12,897) Amortization of net actuarial loss 1,037 773 3,111 2,319 Net periodic benefit cost (credit) $ 209 $ (146) $ 627 $ (438) Components of net periodic benefit credit for the Company's other postretirement benefit plans were as follows: Three Months Ended Nine Months Ended September 30, September 30, 2024 2023 2024 2023 (In thousands) Components of net periodic benefit credit: Service cost $ 126 $ 131 $ 378 $ 405 Interest cost 459 489 1,377 1,467 Expected return on assets (1,329) (1,334) (3,987) (4,026) Amortization of prior service credit (330) (330) (990) (989) Amortization of net actuarial gain (72) (96) (216) (408) Net periodic benefit credit, including amount capitalized (1,146) (1,140) (3,438) (3,551) Less amount capitalized 25 23 72 76 Net periodic benefit credit $ (1,171) $ (1,163) $ (3,510) $ (3,627) The components of net periodic benefit cost (credit), other than the service cost component, are included in Other income on the Consolidated Statements of Income. The service cost component is included in Operation and maintenance expense on the Consolidated Statements of Income. Nonqualified defined benefit plans In addition to the qualified defined benefit pension plans reflected in the table at the beginning of this note, the Company also has unfunded, nonqualified defined benefit plans for executive officers and certain key management employees. The Company's net periodic benefit cost for these plans was $733,000 and $759,000 for the three months ended September 30, 2024 and 2023, respectively, and $2.2 million and $2.3 million for the nine months ended September 30, 2024 and 2023, respectively. The components of net periodic benefit cost for these plans are included in Other income on the Consolidated Statements of Income.

Regulatory matters

Regulatory matters	9 Months Ended
	Sep. 30, 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 including updates to those reported in the 2023 Annual Report and should be read in conjunction with previous filings. 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. This matter is pending before the MTPSC. 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. This matter is pending before the NDPSC. 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. SDPUC On August 15, 2023, Montana-Dakota filed a request with the SDPUC for an electric general rate increase of approximately $3.0 million annually or 17.3 percent above current rates. The requested increase is primarily to recover investments in production, transmission and distribution facilities and the associated depreciation, operation and maintenance expense and taxes associated with the increased investment. On January 26, 2024, Montana-Dakota filed a notice of intent to implement interim rates of $2.7 million annually or 15.4 percent above current rates. The interim rates, subject to refund, were effective March 1, 2024. On July 26, 2024, an all-party settlement agreement was filed reflecting an annual revenue increase of $1.4 million or 8.6 percent overall. The reduction from the original filing includes changes to the overall return, lower depreciation rates and other settled items. On August 13, 2024, the SDPUC approved the settlement with rates effective on and after September 1, 2024. On August 15, 2023, Montana-Dakota filed a request with the SDPUC for a natural gas general rate increase of approximately $7.4 million annually or 11.2 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 January 26, 2024, Montana-Dakota filed a notice of intent to implement interim rates, subject to refund, which were effective March 1, 2024. On July 26, 2024, an all-party settlement agreement was filed reflecting an annual revenue increase of $5.4 million or 8.1 percent overall. The reduction from the original filing includes lower depreciation rates, changes to the overall return and other settled items. On August 13, 2024, the SDPUC approved the settlement with rates effective on and after September 1, 2024. 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 November 5, 2024, Cascade provided formal notice to the Administrative Law Judge that a settlement in principle has been reached. This matter is pending before the WUTC. WYPSC On October 31, 2024, Montana-Dakota filed a request with the WYPSC for a natural gas general rate increase of approximately $2.6 million annually or 14.0 percent above current rates. The requested increase is primarily to recover investments in system upgrades and pipeline replacement projects enhancing the reliability, safety and integrity of the natural gas system, as well as increased costs to operate and maintain that system. This matter is pending before the WYPSC. FERC On August 29, 2024, Montana-Dakota filed an update to its transmission formula rate under the MISO tariff for its multi-value project and network upgrade changes for $19.7 million to be effective January 1, 2025.

Contingencies

Contingencies	9 Months Ended
	Sep. 30, 2024
Commitments and Contingencies Disclosure [Abstract]
Contingencies	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 September 30, 2024 and 2023, and December 31, 2023, the Company accrued liabilities, which have not been discounted, of $23.5 million, $21.0 million and $22.5 million, respectively. At September 30, 2024 and 2023, and December 31, 2023, the Company also recorded corresponding insurance receivables of $1.5 million, $98,000 and $202,000, respectively, and regulatory assets of $20.9 million, $20.1 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 The Company is a party to claims for the cleanup of environmental contamination at certain manufactured gas plant sites. There were no material changes to the Company's environmental matters that were previously reported in the 2023 Annual Report. Guarantees Certain subsidiaries of the Company have outstanding guarantees to third parties that guarantee the performance of other subsidiaries of the Company. These guarantees are related to construction contracts, insurance deductibles and loss limits, and certain other guarantees. At September 30, 2024, the fixed maximum amounts guaranteed under these agreements aggregate $557.5 million. Certain of the guarantees also have no fixed maximum amounts specified. At September 30, 2024, the amounts of scheduled expiration of the maximum amounts guaranteed under these agreements aggregate to $13.3 million in 2024; $186.7 million in 2025; $312.6 million in 2026; $43.5 million in 2027; $1.0 million in 2028; and $400,000 thereafter. There were no amounts outstanding under the previously mentioned guarantees at September 30, 2024. In the event of default under these guarantee obligations, the subsidiary issuing the guarantee for that particular obligation would be required to make payments under its guarantee. 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 September 30, 2024, the fixed maximum amounts guaranteed under these letters of credit aggregated $14.3 million, with the scheduled expiration of the maximum amounts guaranteed under these letters aggregate $12.3 million in 2024 and $2.0 million in 2025. There were no amounts outstanding under the previously mentioned letters of credit at September 30, 2024. In the event of default under these letter of credit obligations, the subsidiary guaranteeing the letter of credit would be obligated for reimbursement of payments made under the letter of credit. In addition, Centennial and Everus Construction have issued guarantees to third parties related to the routine purchase of maintenance items, materials and lease obligations for which no fixed maximum amounts have been specified. These guarantees have no scheduled maturity date. In the event a subsidiary of the Company defaults under these obligations, Centennial or Everus Construction would be required to make payments under these guarantees. Any amounts outstanding by subsidiaries of the Company were reflected on the Consolidated Balance Sheet at September 30, 2024. In the normal course of business, Centennial has surety bonds related to construction contracts and reclamation obligations of its subsidiaries. In the event a subsidiary of Centennial does not fulfill a bonded obligation, Centennial would be responsible to the surety bond company for completion of the bonded contract or obligation. A large portion of the surety bonds is expected to expire within the next 12 months; however, Centennial will likely continue to enter into surety bonds for its subsidiaries in the future. At September 30, 2024, approximately $848.2 million of surety bonds were outstanding, which were not reflected on the Consolidated Balance Sheet. 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 September 30, 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 $26.1 million.

Subsequent event

Subsequent event	9 Months Ended
	Sep. 30, 2024
Subsequent Events [Abstract]
Subsequent event	Subsequent event 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 distribution is expected to be tax-free to the Company's stockholders for U.S. federal income tax purposes, except for cash received in lieu of fractional shares. More information on the separation and distribution can be found within Everus' Form 10, which is not incorporated by reference herein. On November 1, 2024, the Company repaid its outstanding balance of $190.0 million on its $375.0 million term loan agreement which the Company entered into on May 31, 2023, with a SOFR-based variable interest rate and a maturity date of May 31, 2025. The Company's repayment was facilitated by the repayment of debt proceeds from Everus in connection with the separation and the term loan agreement was subsequently terminated.

Pay vs Performance Disclosure

Pay vs Performance Disclosure - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2024	Sep. 30, 2023
Pay vs Performance Disclosure
Net income	$ 64,615	$ 60,436	$ 100,898	$ 74,929	$ 130,692	$ 38,353	$ 225,950	$ 243,974

Insider Trading Arrangements

Insider Trading Arrangements	3 Months Ended
	Sep. 30, 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

Basis of presentation (Policies

Basis of presentation (Policies)	9 Months Ended
	Sep. 30, 2024
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of presentation	The accompanying consolidated interim financial statements were prepared in accordance with GAAP for interim financial information and with the instructions to Form 10-Q and Rule 10-01 of Regulation S-X. Interim financial statements do not include all disclosures provided in annual financial statements and, accordingly, these financial statements should be read in conjunction with those appearing in the 2023 Annual Report. The information is unaudited but includes all adjustments that are, in the opinion of management, necessary for a fair presentation of the accompanying consolidated interim financial statements and are of a normal recurring nature. Depreciation and amortization expense is reported separately on the Consolidated Statements of Income and therefore is excluded from the other line items within operating expenses.
New accounting standards	The following table provides a brief description of the accounting pronouncements applicable to the Company and the potential impact on its Consolidated 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 was beyond the 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 does not expect the guidance to have a material impact on its results of operations, financial position, cash flows or disclosures. Recently issued accounting standards not yet adopted ASU 2023-05 Business Combinations - Joint Venture Formations - Recognition and Initial Measurement In August 2023, the FASB issued guidance on accounting for contributions made to a joint venture, upon formation, in a joint venture's separate financial statement in order to provide decision-useful information to investors and other allocators of capital (collectively investors) in a joint venture's financial statements and reduce diversity in practice. The new basis of accounting will require that a joint venture, upon formation, will recognize and initially measure its assets and liabilities at fair value (with the exceptions to fair value measurement that are consistent with the business combinations guidance). A joint venture that was formed before January 1, 2025 may elect to apply the guidance retrospectively if it has sufficient information. Effective prospectively for all joint venture formations with a formation date on or after January 1, 2025. The Company is currently evaluating the impact the guidance will have on its interim and annual disclosures for the year ended December 31, 2025. 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. Effective for fiscal year December 31, 2024 and interim periods beginning January 1, 2025, with prior periods disclosed in the period of adoption. The Company is currently evaluating the impact the guidance will have on its disclosures for the year ended December 31, 2024 and future interim periods. ASU 2023-09 Income Taxes - Improvements to Income Tax Disclosures an Amendment, 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. December 31, 2025 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 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.
Discontinued operations	As a result of the separation, the historical results of operations are shown in discontinued operations, net of tax, other than allocated general corporate overhead costs of the Company, which do not meet the criteria for income (loss) from discontinued operations.
Expected credit loss	The Company's expected credit losses are determined through a review using historical credit loss experience; changes in asset specific characteristics; current conditions; and reasonable and supportable future forecasts, among other specific account data, and is performed at least quarterly. The Company develops and documents its methodology to determine its allowance for expected credit losses at each of its reportable business segments. Risk characteristics used by the business segments may include customer mix, knowledge of customers and general economic conditions of the various local economies, among others. Specific account balances are written off when management determines the amounts to be uncollectible.
Inventories and natural gas in storage	Natural gas in storage for the Company's regulated operations is generally valued at lower of cost or market using the last-in, first-out method or lower of cost or net realizable value using the average cost or first-in, first-out method. The majority of all other inventories are valued at the lower of cost or net realizable value using the average cost method.
Earnings per share	Basic earnings per share is computed by dividing net income by the weighted average number of shares of common stock outstanding during the applicable period. Diluted earnings per share is computed by dividing net income by the total of the weighted average number of shares of common stock outstanding during the applicable period, plus the effect of non-vested performance share awards and restricted stock units.
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. The Company recognizes revenue from the sale of emissions allowances allocated under the environmental programs in certain states. The Company has the right to payment when the allowances are sold at auction. Revenue is recognized on a point in time basis within the quarter that the auction is held. The revenues associated with the sale of these allowances are deferred as a component of the respective jurisdiction’s regulatory asset or liability for environmental compliance. For more information on the Company’s regulatory assets and liabilities, see Note 10.
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 10.
Fair value measurements	The Company measures its investments in certain fixed-income and equity securities at fair value with changes in fair value recognized in income.
Investments	The Company did not elect the fair value option, which records gains and losses in income, for its available-for-sale securities, which include mortgage-backed securities and U.S. Treasury securities. These available-for-sale securities are recorded at fair value and are classified as Investments on the Consolidated Balance Sheets.
Business segment data	The Company's reportable segments are those that are based on the Company's method of internal reporting, which generally segregates the strategic business units due to differences in products, services and regulation. The internal reporting of these operating segments is defined based on the reporting and review process used by the Company's chief executive officer.
Contingencies	The Company is party to claims and lawsuits arising out of its business and that of its consolidated subsidiaries, which may include, but are not limited to, matters involving property damage, personal injury, and environmental, contractual, statutory and regulatory obligations. The Company accrues a liability for those contingencies when the incurrence of a loss is probable and the amount can be reasonably estimated. If a range of amounts can be reasonably estimated and no amount within the range is a better estimate than any other amount, then the minimum of the range is accrued. The Company does not accrue liabilities when the likelihood that the liability has been incurred is probable but the amount cannot be reasonably estimated or when the liability is believed to be only reasonably possible or remote. For contingencies where an unfavorable outcome is probable or reasonably possible and which are material, the Company discloses the nature of the contingency and, in some circumstances, an estimate of the possible loss. Accruals are based on the best information available, but in certain situations management is unable to estimate an amount or range of a reasonably possible loss including, but not limited to when: (1) the damages are unsubstantiated or indeterminate, (2) the proceedings are in the early stages, (3) numerous parties are involved, or (4) the matter involves novel or unsettled legal theories.
Variable interest entity	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.

Discontinued operations (Tables

Discontinued operations (Tables)	9 Months Ended
	Sep. 30, 2024
Discontinued Operations and Disposal Groups [Abstract]
Schedule of Discontinued Operations, Including Balance Sheet and Income Statement	The reconciliation of the major classes of income and expense constituting pretax loss from discontinued operations to the after-tax loss from discontinued operations on the Consolidated Statements of Income were as follows: Three Months Ended Nine Months Ended September 30, September 30, 2024 2023 2024 2023 (In thousands) Operating revenues $ — $ — $ — $ 735,259 Operating expenses 270 1,447 431 769,407 Operating (loss) income (270) (1,447) (431) (34,148) Other income — — — 2,382 Interest expense — (66) — 37,545 Loss from discontinued operations before income taxes (270) (1,381) (431) (69,311) Income tax (benefit) expense (2,726) 1,908 (2,750) (3,559) Discontinued operations, net of tax $ 2,456 $ (3,289) $ 2,319 $ (65,752)

Receivables and allowance for_2

Receivables and allowance for expected credit losses (Tables)	9 Months Ended
	Sep. 30, 2024
Credit Loss [Abstract]
Schedule of Accounts Receivable, Allowance for Credit Loss	Details of the Company's expected credit losses were as follows: Electric Natural gas Pipeline Construction Total (In thousands) At December 31, 2023 $ 414 $ 1,189 $ — $ 7,967 $ 9,570 Current expected credit loss provision 782 1,916 — (411) 2,287 Less write-offs charged against the allowance 659 1,455 — 48 2,162 Credit loss recoveries collected 147 314 — — 461 At March 31, 2024 $ 684 $ 1,964 $ — $ 7,508 $ 10,156 Current expected credit loss provision 190 214 — 277 681 Less write-offs charged against the allowance 463 969 — 541 1,973 Credit loss recoveries collected 80 196 — 13 289 At June 30, 2024 $ 491 $ 1,405 $ — $ 7,257 $ 9,153 Current expected credit loss provision 520 1,330 — 84 1,934 Less write-offs charged against the allowance 594 2,121 — 84 2,799 Credit loss recoveries collected 86 255 — 43 384 At September 30, 2024 $ 503 $ 869 $ — $ 7,300 $ 8,672 Electric Natural gas Pipeline Construction Total (In thousands) At December 31, 2022 $ 375 $ 1,615 $ 2 $ 2,162 $ 4,154 Current expected credit loss provision 615 2,324 — 826 3,765 Less write-offs charged against the allowance 667 1,225 — 51 1,943 Credit loss recoveries collected 145 229 — 1 375 At March 31, 2023 $ 468 $ 2,943 $ 2 $ 2,938 $ 6,351 Current expected credit loss provision 182 90 — 1,825 2,097 Less write-offs charged against the allowance 316 1,454 — 103 1,873 Credit loss recoveries collected 79 161 — 58 298 At June 30, 2023 $ 413 $ 1,740 $ 2 $ 4,718 $ 6,873 Current expected credit loss provision 513 1,661 — 1,733 3,907 Less write-offs charged against the allowance 572 2,758 — 27 3,357 Credit loss recoveries collected 75 233 — — 308 At September 30, 2023 $ 429 $ 876 $ 2 $ 6,424 $ 7,731

Inventories and natural gas i_2

Inventories and natural gas in storage (Tables)	9 Months Ended
	Sep. 30, 2024
Inventory Disclosure [Abstract]
Schedule of Inventories	Inventories on the Consolidated Balance Sheets were as follows: September 30, 2024 September 30, 2023 December 31, 2023 (In thousands) Natural gas in storage (current) $ 40,770 $ 29,821 $ 39,377 Merchandise for resale 38,311 36,815 34,955 Materials and supplies 6,264 7,824 5,460 Other 6,544 5,775 7,600 Total $ 91,889 $ 80,235 $ 87,392

Earnings per share (Tables)

Earnings per share (Tables)	9 Months Ended
	Sep. 30, 2024
Earnings Per Share [Abstract]
Schedule of Weighted average common shares outstanding	A reconciliation of the weighted average common shares outstanding used in the basic and diluted earnings per share calculations follows: Three Months Ended Nine Months Ended September 30, September 30, 2024 2023 2024 2023 (In thousands, except per share amounts) Weighted average common shares outstanding - basic 203,888 203,638 203,852 203,633 Effect of dilutive performance share awards and restricted stock units 790 248 599 258 Weighted average common shares outstanding - diluted 204,678 203,886 204,451 203,891 Earnings per share - basic: Income from continuing operations $ .31 $ .38 $ 1.10 $ 1.52 Discontinued operations, net of tax .01 (.01) .01 (.32) Earnings per share - basic $ .32 $ .37 $ 1.11 $ 1.20 Earnings per share - diluted: Income from continuing operations $ .31 $ .38 $ 1.10 $ 1.52 Discontinued operations, net of tax .01 (.01) .01 (.32) Earnings per share - diluted $ .32 $ .37 $ 1.11 $ 1.20 Shares excluded from the calculation of diluted earnings per share — — — — Dividends declared per common share $ .1300 $ .1250 $ .3800 $ .5700

Revenue from contracts with c_2

Revenue from contracts with customers (Tables)	9 Months Ended
	Sep. 30, 2024
Revenue from Contract with Customer [Abstract]
Schedule of Disaggregation of revenue	In the following tables, revenue is disaggregated by the type of customer or service provided. The Company believes this level of disaggregation best depicts how the nature, amount, timing and uncertainty of revenue and cash flows are affected by economic factors. The table also includes a reconciliation of the disaggregated revenue by reportable segments. For more information on the Company's business segments, see Note 15. Three Months Ended September 30, 2024 Electric Natural gas Pipeline Construction Other Total (In thousands) Residential utility sales $ 37,076 $ 61,928 $ — $ — $ — $ 99,004 Commercial utility sales 46,648 37,687 — — — 84,335 Industrial utility sales 9,702 6,869 — — — 16,571 Other utility sales 2,045 — — — — 2,045 Natural gas transportation — 15,279 41,936 — — 57,215 Natural gas storage — — 6,053 — — 6,053 Electrical & mechanical specialty contracting — — — 534,613 — 534,613 Transmission & distribution specialty contracting — — — 216,062 — 216,062 Other 16,182 9,736 3,537 169 1,433 31,057 Intersegment eliminations (96) (104) (3,931) — (1,432) (5,563) Revenues from contracts with customers 111,557 131,395 47,595 750,844 1 1,041,392 Other revenues (3,173) 2,122 33 10,142 — 9,124 Total external operating revenues $ 108,384 $ 133,517 $ 47,628 $ 760,986 $ 1 $ 1,050,516 Three Months Ended September 30, 2023 Electric Natural gas Pipeline Construction Other Total (In thousands) Residential utility sales $ 34,303 $ 68,733 $ — $ — $ — $ 103,036 Commercial utility sales 49,754 40,360 — — — 90,114 Industrial utility sales 10,747 7,272 — — — 18,019 Other utility sales 1,865 — — — — 1,865 Natural gas transportation — 13,050 35,338 — — 48,388 Natural gas storage — — 4,808 — — 4,808 Electrical & mechanical specialty contracting — — — 514,378 — 514,378 Transmission & distribution specialty contracting — — — 192,056 — 192,056 Other 14,701 3,881 3,916 (89) 1,689 24,098 Intersegment eliminations (27) (69) (3,701) — (1,689) (5,486) Revenues from contracts with customers 111,343 133,227 40,361 706,345 — 991,276 Other revenues (3,254) 1,669 43 11,061 — 9,519 Total external operating revenues $ 108,089 $ 134,896 $ 40,404 $ 717,406 $ — $ 1,000,795 Nine Months Ended September 30, 2024 Electric Natural gas Pipeline Construction Other Total (In thousands) Residential utility sales $ 107,735 $ 431,721 $ — $ — $ — $ 539,456 Commercial utility sales 129,783 264,091 — — — 393,874 Industrial utility sales 32,809 30,716 — — — 63,525 Other utility sales 6,046 — — — — 6,046 Natural gas transportation — 43,194 128,979 — — 172,173 Natural gas storage — — 16,766 — — 16,766 Electrical & mechanical specialty contracting — — — 1,476,006 — 1,476,006 Transmission & distribution specialty contracting — — — 583,803 — 583,803 Other 44,998 18,705 9,903 260 4,283 78,149 Intersegment eliminations (188) (209) (43,296) (336) (4,265) (48,294) Revenues from contracts with customers 321,183 788,218 112,352 2,059,733 18 3,281,504 Revenues out of scope (5,915) 6,200 119 29,978 — 30,382 Total external operating revenues $ 315,268 $ 794,418 $ 112,471 $ 2,089,711 $ 18 $ 3,311,886 Nine Months Ended September 30, 2023 Electric Natural gas Pipeline Construction Other Total (In thousands) Residential utility sales $ 102,953 $ 517,351 $ — $ — $ — $ 620,304 Commercial utility sales 124,363 316,483 — — — 440,846 Industrial utility sales 31,880 33,293 — — — 65,173 Other utility sales 5,349 — — — — 5,349 Natural gas transportation — 38,225 104,716 — — 142,941 Natural gas storage — — 12,427 — — 12,427 Electrical & mechanical specialty contracting — — — 1,672,948 — 1,672,948 Transmission & distribution specialty contracting — — — 511,563 — 511,563 Other 38,111 11,874 9,713 121 6,412 66,231 Intersegment eliminations (82) (208) (37,889) — (6,412) (44,591) Revenues from contracts with customers 302,574 917,018 88,967 2,184,632 — 3,493,191 Revenues out of scope (7,799) 2,469 119 34,040 — 28,829 Total external operating revenues $ 294,775 $ 919,487 $ 89,086 $ 2,218,672 $ — $ 3,522,020
Schedule of Contract balances	The changes in contract assets and liabilities were as follows: September 30, 2024 December 31, 2023 Change Location on Consolidated Balance Sheets (In thousands) Contract assets $ 174,782 $ 158,861 $ 15,921 Receivables, net Contract liabilities - current (226,754) (202,144) (24,610) Accounts payable Contract liabilities - noncurrent (2,114) (291) (1,823) Noncurrent liabilities - other Net contract liabilities $ (54,086) $ (43,574) $ (10,512)

Regulatory assets and liabili_2

Regulatory assets and liabilities (Tables)	9 Months Ended
	Sep. 30, 2024
Regulatory Assets and Liabilities Disclosure [Abstract]
Schedule of Regulatory Assets	The following table summarizes the individual components of unamortized regulatory assets and liabilities: Estimated Recovery or Refund Period as of September 30, 2024 * September 30, 2024 September 30, 2023 December 31, 2023 (In thousands) Regulatory assets: Current: Natural gas costs recoverable through rate adjustments Up to 1 year $ 111,946 $ 107,101 $ 98,844 Environmental compliance programs Up to 1 year 80,198 3,972 5,525 Conservation programs Up to 1 year 19,059 14,411 14,425 Demand cost deferral Up to 1 year 13,898 13,254 5,207 Electric fuel and purchased power deferral Up to 1 year 4,497 17,775 33,918 Cost recovery mechanisms Up to 1 year 4,332 9,461 9,153 Other Up to 1 year 7,078 3,274 5,420 241,008 169,248 172,492 Noncurrent: Pension and postretirement benefits ** 142,511 144,448 142,511 Cost recovery mechanisms Up to 25 years 82,907 68,539 85,944 Plant costs/asset retirement obligations Over plant lives 45,249 43,520 46,009 Manufactured gas plant site remediation - 25,789 24,577 26,127 Taxes recoverable from customers Over plant lives 12,316 12,266 12,249 Natural gas costs recoverable through rate adjustments Up to 2 years 11,707 64,914 55,493 Electric fuel and purchased power deferral Up to 2 years 8,335 — — Environmental compliance programs - 2,858 36,605 66,806 Long-term debt refinancing costs Up to 36 years 2,159 2,747 2,600 Plant to be retired - 22 19,947 772 Other Up to 15 years 9,725 11,406 8,588 343,578 428,969 447,099 Total regulatory assets $ 584,586 $ 598,217 $ 619,591 Regulatory liabilities: Current: Environmental compliance programs Up to 1 year $ 77,392 $ — $ — Natural gas costs refundable through rate adjustments Up to 1 year 54,197 20,445 43,161 Provision for rate refund Up to 1 year 8,868 2,717 6,866 Margin sharing Up to 1 year 3,945 2,697 5,243 Conservation programs Up to 1 year 2,662 1,976 2,130 Cost recovery mechanisms Up to 1 year 2,634 5,754 6,284 Taxes refundable to customers Up to 1 year 2,195 1,513 2,149 Other Up to 1 year 5,175 9,911 4,928 157,068 45,013 70,761 Noncurrent: Plant removal and decommissioning costs Over plant lives 224,839 220,499 220,147 Taxes refundable to customers Over plant lives 184,715 194,804 193,578 Cost recovery mechanisms Up to 18 years 28,397 20,012 21,791 Accumulated deferred investment tax credit Over plant lives 17,679 14,800 15,740 Pension and postretirement benefits ** 6,043 7,120 6,044 Environmental compliance programs - — 36,126 61,941 Other Up to 14 years 2,117 1,751 1,809 463,790 495,112 521,050 Total regulatory liabilities $ 620,858 $ 540,125 $ 591,811 Net regulatory position $ (36,272) $ 58,092 $ 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: Estimated Recovery or Refund Period as of September 30, 2024 * September 30, 2024 September 30, 2023 December 31, 2023 (In thousands) Regulatory assets: Current: Natural gas costs recoverable through rate adjustments Up to 1 year $ 111,946 $ 107,101 $ 98,844 Environmental compliance programs Up to 1 year 80,198 3,972 5,525 Conservation programs Up to 1 year 19,059 14,411 14,425 Demand cost deferral Up to 1 year 13,898 13,254 5,207 Electric fuel and purchased power deferral Up to 1 year 4,497 17,775 33,918 Cost recovery mechanisms Up to 1 year 4,332 9,461 9,153 Other Up to 1 year 7,078 3,274 5,420 241,008 169,248 172,492 Noncurrent: Pension and postretirement benefits ** 142,511 144,448 142,511 Cost recovery mechanisms Up to 25 years 82,907 68,539 85,944 Plant costs/asset retirement obligations Over plant lives 45,249 43,520 46,009 Manufactured gas plant site remediation - 25,789 24,577 26,127 Taxes recoverable from customers Over plant lives 12,316 12,266 12,249 Natural gas costs recoverable through rate adjustments Up to 2 years 11,707 64,914 55,493 Electric fuel and purchased power deferral Up to 2 years 8,335 — — Environmental compliance programs - 2,858 36,605 66,806 Long-term debt refinancing costs Up to 36 years 2,159 2,747 2,600 Plant to be retired - 22 19,947 772 Other Up to 15 years 9,725 11,406 8,588 343,578 428,969 447,099 Total regulatory assets $ 584,586 $ 598,217 $ 619,591 Regulatory liabilities: Current: Environmental compliance programs Up to 1 year $ 77,392 $ — $ — Natural gas costs refundable through rate adjustments Up to 1 year 54,197 20,445 43,161 Provision for rate refund Up to 1 year 8,868 2,717 6,866 Margin sharing Up to 1 year 3,945 2,697 5,243 Conservation programs Up to 1 year 2,662 1,976 2,130 Cost recovery mechanisms Up to 1 year 2,634 5,754 6,284 Taxes refundable to customers Up to 1 year 2,195 1,513 2,149 Other Up to 1 year 5,175 9,911 4,928 157,068 45,013 70,761 Noncurrent: Plant removal and decommissioning costs Over plant lives 224,839 220,499 220,147 Taxes refundable to customers Over plant lives 184,715 194,804 193,578 Cost recovery mechanisms Up to 18 years 28,397 20,012 21,791 Accumulated deferred investment tax credit Over plant lives 17,679 14,800 15,740 Pension and postretirement benefits ** 6,043 7,120 6,044 Environmental compliance programs - — 36,126 61,941 Other Up to 14 years 2,117 1,751 1,809 463,790 495,112 521,050 Total regulatory liabilities $ 620,858 $ 540,125 $ 591,811 Net regulatory position $ (36,272) $ 58,092 $ 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)	9 Months Ended
	Sep. 30, 2024
Fair Value Disclosures [Abstract]
Schedule of Available-for-Sale Securities	Details of available-for-sale securities were as follows: September 30, 2024 Cost Gross Gross Fair Value (In thousands) Mortgage-backed securities $ 8,104 $ 41 $ 312 $ 7,833 U.S. Treasury securities 3,897 74 — 3,971 Total $ 12,001 $ 115 $ 312 $ 11,804 September 30, 2023 Cost Gross Gross Fair Value (In thousands) Mortgage-backed securities $ 8,386 $ — $ 750 $ 7,636 U.S. Treasury securities 3,307 11 23 3,295 Total $ 11,693 $ 11 $ 773 $ 10,931 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 Assets and liabilities measured at fair value on a recurring basis	The Company's assets measured at fair value on a recurring basis were as follows: Fair Value Measurements at September 30, 2024, Using Quoted Prices in Significant Significant Balance at September 30, 2024 (In thousands) Assets: Money market funds $ — $ 11,033 $ — $ 11,033 Insurance contracts* — 63,658 — 63,658 Available-for-sale securities: Mortgage-backed securities — 7,833 — 7,833 U.S. Treasury securities — 3,971 — 3,971 Total assets measured at fair value $ — $ 86,495 $ — $ 86,495 * The insurance contracts invest approximately 55 percent in fixed-income investments, 18 percent in common stock of large-cap companies, 10 percent in target date investments, 8 percent in common stock of mid-cap companies, 4 percent in common stock of small-cap companies, 4 percent in cash equivalents, and 1 percent in international investments. Fair Value Measurements at September 30, 2023, Using Quoted Prices in Significant Significant Balance at September 30, 2023 (In thousands) Assets: Retained shares in Knife River $ 276,213 $ — $ — $ 276,213 Money market funds — 25,818 — 25,818 Insurance contracts* — 62,736 — 62,736 Available-for-sale securities: Mortgage-backed securities — 7,637 — 7,637 U.S. Treasury securities — 3,295 — 3,295 Total assets measured at fair value $ 276,213 $ 99,486 $ — $ 375,699 * The insurance contracts invest approximately 50 percent in fixed-income investments, 19 percent in common stock of large-cap companies, 10 percent in target date investments, 10 percent in common stock of mid-cap companies, 6 percent in common stock of small-cap companies, 3 percent in cash equivalents, 1 percent in international investments, and 1 percent in high-yield investments. Fair Value Measurements at December 31, 2023, Using Quoted Prices in Significant Significant Balance at December 31, 2023 (In thousands) Assets: Money market funds $ — $ 6,409 $ — $ 6,409 Insurance contracts* — 66,283 — 66,283 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 $ — $ 84,014 $ — $ 84,014 * 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 of long term debt outstanding	The estimated fair value of the Company's Level 2 long-term debt was as follows: September 30, 2024 September 30, 2023 December 31, 2023 (In thousands) Carrying amount $ 2,452,297 $ 2,341,147 $ 2,298,223 Fair value $ 2,207,359 $ 1,960,926 $ 2,046,039

Debt (Tables)

Debt (Tables)	9 Months Ended
	Sep. 30, 2024
Debt Disclosure [Abstract]
Schedule of Long-term debt outstanding	Long-term debt outstanding was as follows: Weighted Average Interest Rate at September 30, 2024 September 30, 2024 September 30, 2023 December 31, 2023 (In thousands) Senior Notes due on dates ranging from August 23, 2025 to June 15, 2062 4.57 % $ 1,947,000 $ 1,757,000 $ 1,882,000 Term Loan Agreements due on dates ranging from May 31, 2025 to April 1, 2039 5.67 % 255,600 381,300 196,300 Credit agreements due on June 20, 2029 6.57 % 163,500 38,900 46,100 Commercial paper supported by revolving credit agreement 5.31 % 57,800 97,700 144,200 Medium-Term Notes due on dates ranging from September 15, 2027 to March 16, 2029 7.32 % 35,000 35,000 35,000 Other notes due on dates ranging from May 31, 2028 to November 30, 2038 6.00 % 350 37,884 980 Less unamortized debt issuance costs 6,953 6,637 6,357 Total long-term debt 2,452,297 2,341,147 2,298,223 Less current maturities 218,777 61,319 61,319 Net long-term debt $ 2,233,520 $ 2,279,828 $ 2,236,904
Schedule of debt maturities	Long-term debt maturities, which excludes unamortized debt issuance costs and discount, at September 30, 2024, were as follows: Remainder of 2024 2025 2026 2027 2028 Thereafter (In thousands) Long-term debt maturities $ — $ 351,700 $ 144,700 $ 24,700 $ 137,500 $ 1,800,650

Cash flow information (Tables)

Cash flow information (Tables)	9 Months Ended
	Sep. 30, 2024
Supplemental Cash Flow Information [Abstract]
Schedule of Cash Expenditures for Interest and Income Taxes and Noncash Investing and Financing Transactions	Cash expenditures for interest and income taxes were as follows: Nine Months Ended September 30, 2024 2023 (In thousands) Interest, net* $ 74,504 $ 84,352 Income taxes paid, net** $ 53,553 $ 40,290 * AFUDC - borrowed was $8.4 million and $7.4 million for the nine months ended September 30, 2024 and 2023, respectively. Interest, net also includes interest classified as discontinued operations in 2023. ** Income taxes paid, including discontinued operations, was $39.4 million for the nine months ended September 30, 2023. Noncash investing and financing transactions were as follows: September 30, 2024 September 30, 2023 December 31, 2023 (In thousands) Right-of-use assets obtained in exchange for new operating lease liabilities $ 39,558 $ 36,307 $ 46,181 Property, plant and equipment additions in accounts payable $ 49,686 $ 37,598 $ 46,622

Business segment data (Tables)

Business segment data (Tables)	9 Months Ended
	Sep. 30, 2024
Segment Reporting [Abstract]
Schedule of Information on the Company's businesses	Information on the Company's segments was as follows: Three Months Ended Nine Months Ended September 30, September 30, 2024 2023 2024 2023 (In thousands) External operating revenues: Regulated operations: Electric $ 108,384 $ 108,089 $ 315,268 $ 294,775 Natural gas distribution 133,517 134,896 794,418 919,487 Pipeline 44,152 36,549 102,929 79,697 286,053 279,534 1,212,615 1,293,959 Non-regulated operations: Pipeline 3,476 3,855 9,542 9,389 Construction services 760,986 717,406 2,089,711 2,218,672 Other 1 — 18 — 764,463 721,261 2,099,271 2,228,061 Total external operating revenues $ 1,050,516 $ 1,000,795 $ 3,311,886 $ 3,522,020 Intersegment operating revenues: Regulated operations: Electric $ 96 $ 27 $ 188 $ 82 Natural gas distribution 104 69 209 208 Pipeline 3,904 3,666 43,033 37,624 4,104 3,762 43,430 37,914 Non-regulated operations: Pipeline 27 35 263 265 Construction services — — 336 — Other 1,432 1,689 4,265 6,412 1,459 1,724 4,864 6,677 Total intersegment operating revenues $ 5,563 $ 5,486 $ 48,294 $ 44,591 Operating income (loss): Electric $ 32,079 $ 28,718 $ 73,498 $ 71,372 Natural gas distribution (14,695) (15,258) 44,747 45,674 Pipeline 22,179 17,767 68,101 44,693 Construction services 53,709 50,091 143,902 139,619 Other (2,468) 3,286 (13,751) (16,201) Total operating income $ 90,804 $ 84,604 $ 316,497 $ 285,157 Income (loss) from continuing operations: Regulated operations: Electric $ 24,292 $ 20,942 $ 57,689 $ 53,887 Natural gas distribution (17,481) (17,764) 17,581 18,007 Pipeline 14,810 11,450 47,054 29,029 21,621 14,628 122,324 100,923 Non-regulated operations: Pipeline 374 508 447 337 Construction services 41,767 35,975 108,953 105,951 Other (1,603) 27,107 (8,093) 102,515 40,538 63,590 101,307 208,803 Income from continuing operations 62,159 78,218 223,631 309,726 Discontinued operations, net of tax 2,456 (3,289) 2,319 (65,752) Net income $ 64,615 $ 74,929 $ 225,950 $ 243,974
Schedule of Reconciliation of Revenue from Segments to Consolidated	A reconciliation of reportable segment operating revenues to consolidated operating revenues is as follows: Three Months Ended Nine Months Ended September 30, September 30, 2024 2023 2024 2023 (In thousands) Operating revenues reconciliation: Total reportable segment operating revenues $ 1,054,646 $ 1,004,592 $ 3,355,897 $ 3,560,199 Other revenue 1,433 1,689 4,283 6,412 Elimination of intersegment operating revenues (5,563) (5,486) (48,294) (44,591) Total consolidated operating revenues $ 1,050,516 $ 1,000,795 $ 3,311,886 $ 3,522,020

Employee benefit plans (Tables)

Employee benefit plans (Tables)	9 Months Ended
	Sep. 30, 2024
Retirement Benefits [Abstract]
Schedule of net benefit costs	Components of net periodic benefit cost (credit) for the Company's pension benefit plans were as follows: Three Months Ended Nine Months Ended September 30, September 30, 2024 2023 2024 2023 (In thousands) Components of net periodic benefit cost (credit): Interest cost $ 3,200 $ 3,380 $ 9,600 $ 10,140 Expected return on assets (4,028) (4,299) (12,084) (12,897) Amortization of net actuarial loss 1,037 773 3,111 2,319 Net periodic benefit cost (credit) $ 209 $ (146) $ 627 $ (438) Components of net periodic benefit credit for the Company's other postretirement benefit plans were as follows: Three Months Ended Nine Months Ended September 30, September 30, 2024 2023 2024 2023 (In thousands) Components of net periodic benefit credit: Service cost $ 126 $ 131 $ 378 $ 405 Interest cost 459 489 1,377 1,467 Expected return on assets (1,329) (1,334) (3,987) (4,026) Amortization of prior service credit (330) (330) (990) (989) Amortization of net actuarial gain (72) (96) (216) (408) Net periodic benefit credit, including amount capitalized (1,146) (1,140) (3,438) (3,551) Less amount capitalized 25 23 72 76 Net periodic benefit credit $ (1,171) $ (1,163) $ (3,510) $ (3,627)

Basis of presentation (Details)

Basis of presentation (Details) - Discontinued Operations, Disposed of by Means Other than Sale, Spinoff shares in Millions	Oct. 31, 2024	May 31, 2023 shares
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		4
Retained ownership percentage		0.10
Number of retained shares (in shares)		5.7
Everus | Subsequent Event
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Stock split, conversion ratio	4

Discontinued operations - Narra

Discontinued operations - Narrative (Details) $ in Thousands				3 Months Ended		9 Months Ended
	May 31, 2024 shares	May 31, 2023 shares	Apr. 25, 2023 USD ($)	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)	Dec. 31, 2023 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Long-term debt				$ 2,452,297	$ 2,341,147	$ 2,452,297	$ 2,341,147	$ 2,298,223
Repayment of long-term debt						147,731	434,994
Treasury stock retired (in shares) | shares	538,921
Separation related costs				204	1,000	342	47,100
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		4
Retained ownership percentage		0.10
Number of retained shares (in shares) | shares		5,700,000
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				39	1,300	1,500	1,900
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				$ 15	$ 407	$ 155	$ 684
Knife River Corporation
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Repayment 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 - Sched

Discontinued operations - Schedule of Income and Expense Constituting Pretax Income (Loss) From Discontinued Operations (Details) - Knife River Corporation - Discontinued Operations, Disposed of by Means Other than Sale, Spinoff - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Operating revenues	$ 0	$ 0	$ 0	$ 735,259
Operating expenses	270	1,447	431	769,407
Operating (loss) income	(270)	(1,447)	(431)	(34,148)
Other income	0	0	0	2,382
Interest expense	0	(66)	0	37,545
Loss from discontinued operations before income taxes	(270)	(1,381)	(431)	(69,311)
Income tax (benefit) expense	(2,726)	1,908	(2,750)	(3,559)
Discontinued operations, net of tax	$ 2,456	$ (3,289)	$ 2,319	$ (65,752)

Receivables and allowance for_3

Receivables and allowance for expected credit losses - Narrative (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023	Sep. 30, 2023
Credit Loss [Abstract]
Accounts receivable, noncurrent, 90 days or more past due, still accruing	$ 79.9	$ 45.7	$ 51.1

Receivables and allowance for_4

Receivables and allowance for expected credit losses - Schedule of Accounts Receivable, Allowance for Credit Loss (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2024	Sep. 30, 2023
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Current expected credit loss provision							$ 4,902	$ 9,769
Trade Accounts Receivable
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	$ 9,153	$ 10,156	$ 9,570	$ 6,873	$ 6,351	$ 4,154	9,570	4,154
Current expected credit loss provision	1,934	681	2,287	3,907	2,097	3,765
Less write-offs charged against the allowance	2,799	1,973	2,162	3,357	1,873	1,943
Credit loss recoveries collected	384	289	461	308	298	375
Ending balance	8,672	9,153	10,156	7,731	6,873	6,351	8,672	7,731
Electric | Trade Accounts Receivable
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	491	684	414	413	468	375	414	375
Current expected credit loss provision	520	190	782	513	182	615
Less write-offs charged against the allowance	594	463	659	572	316	667
Credit loss recoveries collected	86	80	147	75	79	145
Ending balance	503	491	684	429	413	468	503	429
Natural gas distribution | Trade Accounts Receivable
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	1,405	1,964	1,189	1,740	2,943	1,615	1,189	1,615
Current expected credit loss provision	1,330	214	1,916	1,661	90	2,324
Less write-offs charged against the allowance	2,121	969	1,455	2,758	1,454	1,225
Credit loss recoveries collected	255	196	314	233	161	229
Ending balance	869	1,405	1,964	876	1,740	2,943	869	876
Pipeline | Trade Accounts Receivable
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	0	0	0	2	2	2	0	2
Current expected credit loss provision	0	0	0	0	0	0
Less write-offs charged against the allowance	0	0	0	0	0	0
Credit loss recoveries collected	0	0	0	0	0	0
Ending balance	0	0	0	2	2	2	0	2
Construction services | Trade Accounts Receivable
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	7,257	7,508	7,967	4,718	2,938	2,162	7,967	2,162
Current expected credit loss provision	84	277	(411)	1,733	1,825	826
Less write-offs charged against the allowance	84	541	48	27	103	51
Credit loss recoveries collected	43	13	0	0	58	1
Ending balance	$ 7,300	$ 7,257	$ 7,508	$ 6,424	$ 4,718	$ 2,938	$ 7,300	$ 6,424

Inventories and natural gas i_3

Inventories and natural gas in storage (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023	Sep. 30, 2023
Inventory Disclosure [Abstract]
Natural gas in storage (current)	$ 40,770	$ 39,377	$ 29,821
Merchandise for resale	38,311	34,955	36,815
Materials and supplies	6,264	5,460	7,824
Other	6,544	7,600	5,775
Total	91,889	87,392	80,235
Natural gas in storage noncurrent	$ 50,100	$ 48,500	$ 47,400

Earnings per share - Schedule o

Earnings per share - Schedule of Weighted Average Number of Shares (Details) - $ / shares shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Earnings Per Share [Abstract]
Weighted average common shares outstanding - basic (in shares)	203,888	203,638	203,852	203,633
Effect of dilutive performance share awards and restricted stock units (in shares)	790	248	599	258
Weighted average common shares outstanding - diluted (in shares)	204,678	203,886	204,451	203,891
Earnings per share - basic:
Income from continuing operations (in usd per share)	$ 0.31	$ 0.38	$ 1.10	$ 1.52
Discontinued operations, net of tax (in usd per share)	0.01	(0.01)	0.01	(0.32)
Earnings per share - basic (in usd per share)	0.32	0.37	1.11	1.20
Earnings per share - diluted:
Income from continuing operations (in usd per share)	0.31	0.38	1.10	1.52
Discontinued operations, net of tax (in usd per share)	0.01	(0.01)	0.01	(0.32)
Earnings per share - diluted (in usd per share)	$ 0.32	$ 0.37	$ 1.11	$ 1.20
Shares excluded from the calculation of diluted earnings per share (in shares)	0	0	0	0
Dividends declared per common share (in usd per share)	$ 0.1300	$ 0.1250	$ 0.3800	$ 0.5700

Revenue from contracts with c_3

Revenue from contracts with customers - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Construction contractor, contract cost, subject to uncertainty, amount	$ 31.2		$ 31.2
Contract with customer, liability, revenue recognized	47.4	$ 6.3	169	$ 164.3
Amounts from performance obligations satisfied in prior periods	25.8	$ 20.2	71.8	$ 41.7
Remaining performance obligation, amount	3,500		3,500
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-10-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation, amount	$ 2,300		$ 2,300
Revenue, remaining performance obligation, expected timing of satisfaction, period	12 months		12 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2025-10-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation, amount	$ 681.1		$ 681.1
Revenue, remaining performance obligation, expected timing of satisfaction, period	12 months		12 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-10-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation, amount	$ 551.1		$ 551.1
Revenue, remaining performance obligation, expected timing of satisfaction, period
Construction services
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Contract with customer, term (less than)	2 years		2 years
Pipeline
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Contract with customer, term (less than)	12 months		12 months
Pipeline | Firm Transportation Contract
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Contract weighted average remaining duration (less than)	5 years		5 years
Pipeline | Firm Storage Contract
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Contract weighted average remaining duration (less than)	2 years		2 years

Revenue from contracts with c_4

Revenue from contracts with customers - Schedule of Disaggregation of revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 1,041,392	$ 991,276	$ 3,281,504	$ 3,493,191
Other revenues	9,124	9,519	30,382	28,829
Total external operating revenues	1,050,516	1,000,795	3,311,886	3,522,020
Intersegment eliminations
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	(5,563)	(5,486)	(48,294)	(44,591)
Total external operating revenues	(5,563)	(5,486)	(48,294)	(44,591)
Operating Segments
Disaggregation of Revenue [Line Items]
Total external operating revenues	1,054,646	1,004,592	3,355,897	3,560,199
Natural gas transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	57,215	48,388	172,173	142,941
Natural gas storage
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	6,053	4,808	16,766	12,427
Electrical & mechanical specialty contracting
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	534,613	514,378	1,476,006	1,672,948
Transmission & distribution specialty contracting
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	216,062	192,056	583,803	511,563
Other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	31,057	24,098	78,149	66,231
Residential utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	99,004	103,036	539,456	620,304
Commercial utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	84,335	90,114	393,874	440,846
Industrial utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	16,571	18,019	63,525	65,173
Other utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	2,045	1,865	6,046	5,349
Electric | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	(96)	(27)	(188)	(82)
Electric | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	111,557	111,343	321,183	302,574
Other revenues	(3,173)	(3,254)	(5,915)	(7,799)
Total external operating revenues	108,384	108,089	315,268	294,775
Electric | Natural gas transportation | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Electric | Natural gas storage | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Electric | Electrical & mechanical specialty contracting | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Electric | Transmission & distribution specialty contracting | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Electric | Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	16,182	14,701	44,998	38,111
Electric | Residential utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	37,076	34,303	107,735	102,953
Electric | Commercial utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	46,648	49,754	129,783	124,363
Electric | Industrial utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	9,702	10,747	32,809	31,880
Electric | Other utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	2,045	1,865	6,046	5,349
Natural gas distribution | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	(104)	(69)	(209)	(208)
Natural gas distribution | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	131,395	133,227	788,218	917,018
Other revenues	2,122	1,669	6,200	2,469
Total external operating revenues	133,517	134,896	794,418	919,487
Natural gas distribution | Natural gas transportation | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	15,279	13,050	43,194	38,225
Natural gas distribution | Natural gas storage | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Natural gas distribution | Electrical & mechanical specialty contracting | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Natural gas distribution | Transmission & distribution specialty contracting | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Natural gas distribution | Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	9,736	3,881	18,705	11,874
Natural gas distribution | Residential utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	61,928	68,733	431,721	517,351
Natural gas distribution | Commercial utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	37,687	40,360	264,091	316,483
Natural gas distribution | Industrial utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	6,869	7,272	30,716	33,293
Natural gas distribution | Other utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Pipeline | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	(3,931)	(3,701)	(43,296)	(37,889)
Pipeline | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	47,595	40,361	112,352	88,967
Other revenues	33	43	119	119
Total external operating revenues	47,628	40,404	112,471	89,086
Pipeline | Natural gas transportation | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	41,936	35,338	128,979	104,716
Pipeline | Natural gas storage | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	6,053	4,808	16,766	12,427
Pipeline | Electrical & mechanical specialty contracting | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Pipeline | Transmission & distribution specialty contracting | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Pipeline | Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	3,537	3,916	9,903	9,713
Pipeline | Residential utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Pipeline | Commercial utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Pipeline | Industrial utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Pipeline | Other utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Construction services | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	(336)	0
Construction services | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	750,844	706,345	2,059,733	2,184,632
Other revenues	10,142	11,061	29,978	34,040
Total external operating revenues	760,986	717,406	2,089,711	2,218,672
Construction services | Natural gas transportation | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Construction services | Natural gas storage | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Construction services | Electrical & mechanical specialty contracting | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	534,613	514,378	1,476,006	1,672,948
Construction services | Transmission & distribution specialty contracting | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	216,062	192,056	583,803	511,563
Construction services | Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	169	(89)	260	121
Construction services | Residential utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Construction services | Commercial utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Construction services | Industrial utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Construction services | Other utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Other | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	(1,432)	(1,689)	(4,265)	(6,412)
Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	1	0	18	0
Other revenues	0	0	0	0
Total external operating revenues	1	0	18	0
Other | Natural gas transportation | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Other | Natural gas storage | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Other | Electrical & mechanical specialty contracting | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Other | Transmission & distribution specialty contracting | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Other | Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	1,433	1,689	4,283	6,412
Other | Residential utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Other | Commercial utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Other | Industrial utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Other | Other utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 0	$ 0	$ 0	$ 0

Revenue from contracts with c_5

Revenue from contracts with customers - Schedule of Contract balances (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2024	Dec. 31, 2023
Revenue from Contract with Customer [Abstract]
Contract assets	$ 174,782	$ 158,861
Change in contract assets	15,921
Contract liabilities - current	(226,754)	(202,144)
Change in contract liabilities - current	(24,610)
Contract liabilities - noncurrent	(2,114)	(291)
Change in contract liabilities - noncurrent	(1,823)
Net contract liabilities	(54,086)	$ (43,574)
Change in net contract assets (liabilities)	$ (10,512)

Leases (Details)

Leases (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Leases [Abstract]
Operating lease, lease income	$ 10.3	$ 11.2	$ 30.3	$ 34.5
Lease receivables	$ 8.6		$ 8.6

Regulatory assets and liabili_3

Regulatory assets and liabilities - Schedule of Unamortized Regulatory Assets and Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023	Sep. 30, 2023
Regulatory Asset [Abstract]
Current regulatory assets	$ 241,008	$ 172,492	$ 169,248
Regulatory assets	343,578	447,099	428,969
Total regulatory assets	584,586	619,591	598,217
Regulatory Liability [Abstract]
Regulatory liabilities due within one year	157,068	70,761	45,013
Regulatory liabilities	463,790	521,050	495,112
Total regulatory liabilities	620,858	591,811	540,125
Net regulatory position	$ (36,272)	27,780	58,092
Environmental compliance programs
Regulatory Liability [Abstract]
Estimated Recovery or Refund Period	1 year
Regulatory liabilities due within one year	$ 77,392	0	0
Regulatory liabilities	$ 0	61,941	36,126
Natural gas costs refundable through rate adjustments
Regulatory Liability [Abstract]
Estimated Recovery or Refund Period	1 year
Regulatory liabilities due within one year	$ 54,197	43,161	20,445
Provision for rate refund
Regulatory Liability [Abstract]
Estimated Recovery or Refund Period	1 year
Regulatory liabilities due within one year	$ 8,868	6,866	2,717
Margin sharing
Regulatory Liability [Abstract]
Estimated Recovery or Refund Period	1 year
Regulatory liabilities due within one year	$ 3,945	5,243	2,697
Conservation programs
Regulatory Liability [Abstract]
Estimated Recovery or Refund Period	1 year
Regulatory liabilities due within one year	$ 2,662	2,130	1,976
Cost recovery mechanisms
Regulatory Liability [Abstract]
Regulatory liabilities due within one year	2,634	6,284	5,754
Regulatory liabilities	$ 28,397	21,791	20,012
Taxes recoverable from customers
Regulatory Liability [Abstract]
Estimated Recovery or Refund Period	1 year
Regulatory liabilities due within one year	$ 2,195	2,149	1,513
Regulatory liabilities	184,715	193,578	194,804
Other
Regulatory Liability [Abstract]
Regulatory liabilities due within one year	5,175	4,928	9,911
Regulatory liabilities	2,117	1,809	1,751
Plant removal and decommissioning costs
Regulatory Liability [Abstract]
Regulatory liabilities	224,839	220,147	220,499
Accumulated deferred investment tax credit
Regulatory Liability [Abstract]
Regulatory liabilities	17,679	15,740	14,800
Pension and postretirement benefits
Regulatory Liability [Abstract]
Regulatory liabilities	$ 6,043	6,044	7,120
Minimum | Cost recovery mechanisms
Regulatory Liability [Abstract]
Estimated Recovery or Refund Period	1 year
Minimum | Other
Regulatory Liability [Abstract]
Estimated Recovery or Refund Period	1 year
Maximum | Cost recovery mechanisms
Regulatory Liability [Abstract]
Estimated Recovery or Refund Period	18 years
Maximum | Other
Regulatory Liability [Abstract]
Estimated Recovery or Refund Period	14 years
Natural gas costs recoverable through rate adjustments
Regulatory Asset [Abstract]
Current regulatory assets	$ 111,946	98,844	107,101
Regulatory assets	$ 11,707	55,493	64,914
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]
Estimated Recovery or Refund Period	1 year
Current regulatory assets	$ 80,198	5,525	3,972
Regulatory assets	$ 2,858	66,806	36,605
Conservation programs
Regulatory Asset [Abstract]
Estimated Recovery or Refund Period	1 year
Current regulatory assets	$ 19,059	14,425	14,411
Demand cost deferral
Regulatory Asset [Abstract]
Estimated Recovery or Refund Period	1 year
Current regulatory assets	$ 13,898	5,207	13,254
Electric fuel and purchased power deferral
Regulatory Asset [Abstract]
Current regulatory assets	4,497	33,918	17,775
Regulatory assets	$ 8,335	0	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
Cost recovery mechanisms
Regulatory Asset [Abstract]
Current regulatory assets	$ 4,332	9,153	9,461
Regulatory assets	$ 82,907	85,944	68,539
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	25 years
Other
Regulatory Asset [Abstract]
Current regulatory assets	$ 7,078	5,420	3,274
Regulatory assets	$ 9,725	8,588	11,406
Other | Minimum
Regulatory Asset [Abstract]
Estimated Recovery or Refund Period	1 year
Other | Maximum
Regulatory Asset [Abstract]
Estimated Recovery or Refund Period	15 years
Pension and postretirement benefits
Regulatory Asset [Abstract]
Regulatory assets	$ 142,511	142,511	144,448
Plant costs/asset retirement obligations
Regulatory Asset [Abstract]
Regulatory assets	45,249	46,009	43,520
Manufactured gas plant site remediation
Regulatory Asset [Abstract]
Regulatory assets	25,789	26,127	24,577
Taxes recoverable from customers
Regulatory Asset [Abstract]
Regulatory assets	$ 12,316	12,249	12,266
Long-term debt refinancing costs
Regulatory Asset [Abstract]
Estimated Recovery or Refund Period	36 years
Regulatory assets	$ 2,159	2,600	2,747
Plant removal and decommissioning costs
Regulatory Asset [Abstract]
Regulatory assets	$ 22	$ 772	$ 19,947

Regulatory assets and liabili_4

Regulatory assets and liabilities - Narrative (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023	Sep. 30, 2023
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory assets not earning a rate of return	$ 178.8	$ 194.3	$ 211.8

Fair value measurements - Narra

Fair value measurements - Narrative (Details) $ in Thousands, shares in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2024 USD ($)	Mar. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)	May 31, 2023 shares
Available-for-sale securities [Line Items]
Investments used to satisfy nonqualified benefit plans obligations	$ 63,700		$ 66,200	$ 62,700	$ 63,700	$ 62,700
Net unrealized gain (loss) on investments used to satisfy obligations under nonqualified benefit plans	2,600			(1,400)	5,800	3,500
Investment withdrawal, reduction in cost basis		$ 9,000	20,000
Retained shares in Knife River	0		$ 0	276,213	0	276,213
Unrealized gain on retained shares in Knife River	$ 0			30,150	$ 0	170,170
Discontinued Operations, Disposed of by Means Other than Sale, Spinoff | Knife River Corporation
Available-for-sale securities [Line Items]
Retained ownership percentage							0.10
Number of retained shares (in shares) | shares							5.7
Retained shares in Knife River				276,200		$ 276,200
Unrealized gain on retained shares in Knife River				$ 30,200

Fair value measurements - Sched

Fair value measurements - Schedule of Available-for-Sale Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023	Sep. 30, 2023
Available-for-sale securities [Abstract]
Cost	$ 12,001	$ 11,755	$ 11,693
Gross Unrealized Gains	115	45	11
Gross Unrealized Losses	312	478	773
Fair Value	11,804	11,322	10,931
Mortgage-backed securities
Available-for-sale securities [Abstract]
Cost	8,104	8,234	8,386
Gross Unrealized Gains	41	17	0
Gross Unrealized Losses	312	470	750
Fair Value	7,833	7,781	7,636
U.S. Treasury securities
Available-for-sale securities [Abstract]
Cost	3,897	3,521	3,307
Gross Unrealized Gains	74	28	11
Gross Unrealized Losses	0	8	23
Fair Value	$ 3,971	$ 3,541	$ 3,295

Fair value measurements - Sch_2

Fair value measurements - Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023	Sep. 30, 2023
Concentration risks, percentage [Abstract]
Percentage in fixed-income and other investments	55%	60%	50%
Percentage investment in common stock of large-cap companies	18%	15%	19%
Percentage investment in target date investments	10%	8%	10%
Percentage investment in common stock of mid-cap companies	8%	7%	10%
Percentage investment in common stock of small-cap companies	4%	5%	6%
Percentage investment in cash and cash equivalents	4%	3%	3%
Percentage investment in international investments	1%	1%	1%
Percentage investment in high-yield investments		1%	1%
Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	$ 86,495	$ 84,014	$ 375,699
Fair Value, Inputs, Level 1 | Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	0	0	276,213
Fair value, inputs, level 2 | Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	86,495	84,014	99,486
Fair Value, Inputs, Level 3 | Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	0	0	0
Retained shares in Knife River | Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure			276,213
Retained shares in Knife River | Fair Value, Inputs, Level 1 | Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure			276,213
Retained shares in Knife River | Fair value, inputs, level 2 | Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure			0
Retained shares in Knife River | Fair Value, Inputs, Level 3 | Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure			0
Money market funds | Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	11,033	6,409	25,818
Money market funds | Fair Value, Inputs, Level 1 | Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	0	0	0
Money market funds | Fair value, inputs, level 2 | Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	11,033	6,409	25,818
Money market funds | Fair Value, Inputs, Level 3 | Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	0	0	0
Insurance contracts | Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	63,658	66,283	62,736
Insurance contracts | Fair Value, Inputs, Level 1 | Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	0	0	0
Insurance contracts | Fair value, inputs, level 2 | Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	63,658	66,283	62,736
Insurance contracts | Fair Value, Inputs, Level 3 | Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	0	0	0
Mortgage-backed securities | Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	7,833	7,781	7,637
Mortgage-backed securities | Fair Value, Inputs, Level 1 | Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	0	0	0
Mortgage-backed securities | Fair value, inputs, level 2 | Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	7,833	7,781	7,637
Mortgage-backed securities | Fair Value, Inputs, Level 3 | Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	0	0	0
U.S. Treasury securities | Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	3,971	3,541	3,295
U.S. Treasury securities | Fair Value, Inputs, Level 1 | Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	0	0	0
U.S. Treasury securities | Fair value, inputs, level 2 | Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	3,971	3,541	3,295
U.S. Treasury securities | Fair Value, Inputs, Level 3 | Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	$ 0	$ 0	$ 0

Fair value measurements - Sch_3

Fair value measurements - Schedule of Fair Value, by Balance Sheet Grouping (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023	Sep. 30, 2023
Fair value, balance sheet grouping [Line Items]
Long-term debt	$ 2,452,297	$ 2,298,223	$ 2,341,147
Carrying amount
Fair value, balance sheet grouping [Line Items]
Long-term debt	2,452,297	2,298,223	2,341,147
Fair value
Fair value, balance sheet grouping [Line Items]
Long-term debt, fair value	$ 2,207,359	$ 2,046,039	$ 1,960,926

Debt - Short-Term Debt (Details

Debt - Short-Term Debt (Details) - USD ($) $ in Thousands			1 Months Ended			9 Months Ended
	Jan. 19, 2024	Dec. 05, 2023	May 31, 2023	Apr. 30, 2023	Mar. 31, 2023	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023	Jan. 20, 2023
Short-Term Debt [Line Items]
Short-term borrowings						$ 0	$ 306,400	$ 95,000
Repayment of short-term borrowings						$ 95,000	$ 193,500
Term Loan Agreement | Cascade Natural Gas
Short-Term Debt [Line Items]
Short-term borrowings									$ 150,000
Repayment of short-term borrowings	$ 50,000	$ 100,000
Term Loan Agreement | Intermountain Gas Company
Short-Term Debt [Line Items]
Short-term borrowings									$ 125,000
Repayment of short-term borrowings	$ 45,000		$ 30,000	$ 30,000	$ 20,000

Debt - Long-Term Debt (Details)

Debt - Long-Term Debt (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Jul. 11, 2024	Jun. 20, 2024	Jun. 19, 2024	Apr. 01, 2024	Dec. 31, 2023	Sep. 30, 2023
Long-term debt outstanding [Line Items]
Long-term debt	$ 2,452,297					$ 2,298,223	$ 2,341,147
Revolving Credit Facility | Cascade Natural Gas
Long-term debt outstanding [Line Items]
Line of credit facility, maximum borrowing capacity			$ 175,000	$ 100,000
Ratio of total debt to total capitalization			65%
Revolving Credit Facility | Intermountain Gas Company
Long-term debt outstanding [Line Items]
Line of credit facility, maximum borrowing capacity			$ 175,000	$ 100,000
Ratio of total debt to total capitalization			65%
Term Loan Agreement | WBI Energy Transmission
Long-term debt outstanding [Line Items]
Ratio of total debt to total capitalization					65%
Long-term debt					$ 60,000
Interest rate, stated percentage					4.52%
Debt instrument, annual principal payment					$ 4,000
Senior Notes | Montana-Dakota Utilities Co.
Long-term debt outstanding [Line Items]
Ratio of total debt to total capitalization		65%
Long-term debt		$ 125,000
Interest rate, stated percentage		5.96%

Debt - Schedule of Long-Term De

Debt - Schedule of Long-Term Debt Outstanding (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023	Sep. 30, 2023
Long-term debt outstanding [Line Items]
Less unamortized debt issuance costs	$ 6,953	$ 6,357	$ 6,637
Total long-term debt	2,452,297	2,298,223	2,341,147
Less current maturities	218,777	61,319	61,319
Long-term debt	$ 2,233,520	2,236,904	2,279,828
Senior Notes
Long-term debt outstanding [Line Items]
Weighted Average Interest Rate	4.57%
Long-term debt, gross	$ 1,947,000	1,882,000	1,757,000
Term Loan Agreements
Long-term debt outstanding [Line Items]
Weighted Average Interest Rate	5.67%
Long-term debt, gross	$ 255,600	196,300	381,300
Credit Agreements
Long-term debt outstanding [Line Items]
Weighted Average Interest Rate	6.57%
Long-term debt, gross	$ 163,500	46,100	38,900
Commercial Paper
Long-term debt outstanding [Line Items]
Weighted Average Interest Rate	5.31%
Long-term debt, gross	$ 57,800	144,200	97,700
Medium-term Notes
Long-term debt outstanding [Line Items]
Weighted Average Interest Rate	7.32%
Long-term debt, gross	$ 35,000	35,000	35,000
Other Notes
Long-term debt outstanding [Line Items]
Weighted Average Interest Rate	6%
Long-term debt, gross	$ 350	$ 980	$ 37,884

Debt - Schedule of Debt Maturit

Debt - Schedule of Debt Maturities (Details) $ in Thousands	Sep. 30, 2024 USD ($)
Debt Disclosure [Abstract]
Remainder of 2024	$ 0
2025	351,700
2026	144,700
2027	24,700
2028	137,500
Thereafter	$ 1,800,650

Cash flow information - Schedul

Cash flow information - Schedule of Cash Flow, Supplemental Disclosures (Details) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023
Supplemental Cash Flow Information [Abstract]
Interest, net	$ 74,504	$ 84,352
Income taxes paid, net	53,553	40,290
AFUDC borrowed	8,400	7,400
Income taxes paid, including discontinued operations		39,400
Right-of-use assets obtained in exchange for new operating lease liabilities	39,558	36,307	$ 46,181
Property, plant and equipment additions in accounts payable	$ 49,686	$ 37,598	$ 46,622

Business segment data - Schedul

Business segment data - Schedule of Segment Reporting Information, by Segment (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2024	Sep. 30, 2023
Segment Reporting Information [Line Items]
Revenues	$ 1,050,516			$ 1,000,795			$ 3,311,886	$ 3,522,020
Operating income	90,804			84,604			316,497	285,157
Income from continuing operations	62,159			78,218			223,631	309,726
Discontinued operations, net of tax	2,456			(3,289)			2,319	(65,752)
Net income	64,615	$ 60,436	$ 100,898	74,929	$ 130,692	$ 38,353	225,950	243,974
Operating Segments
Segment Reporting Information [Line Items]
Revenues	1,054,646			1,004,592			3,355,897	3,560,199
Operating Segments | Electric
Segment Reporting Information [Line Items]
Revenues	108,384			108,089			315,268	294,775
Operating income	32,079			28,718			73,498	71,372
Operating Segments | Natural gas distribution
Segment Reporting Information [Line Items]
Revenues	133,517			134,896			794,418	919,487
Operating income	(14,695)			(15,258)			44,747	45,674
Operating Segments | Pipeline
Segment Reporting Information [Line Items]
Revenues	47,628			40,404			112,471	89,086
Operating income	22,179			17,767			68,101	44,693
Operating Segments | Construction services
Segment Reporting Information [Line Items]
Revenues	760,986			717,406			2,089,711	2,218,672
Operating income	53,709			50,091			143,902	139,619
Operating Segments | Other
Segment Reporting Information [Line Items]
Revenues	1			0			18	0
Operating income	(2,468)			3,286			(13,751)	(16,201)
Intersegment eliminations
Segment Reporting Information [Line Items]
Revenues	(5,563)			(5,486)			(48,294)	(44,591)
Regulated operation
Segment Reporting Information [Line Items]
Revenues	286,053			279,534			1,212,615	1,293,959
Income from continuing operations	21,621			14,628			122,324	100,923
Regulated operation | Operating Segments
Segment Reporting Information [Line Items]
Revenues	286,053			279,534			1,212,615	1,293,959
Regulated operation | Operating Segments | Electric
Segment Reporting Information [Line Items]
Revenues	108,384			108,089			315,268	294,775
Income from continuing operations	24,292			20,942			57,689	53,887
Regulated operation | Operating Segments | Natural gas distribution
Segment Reporting Information [Line Items]
Revenues	133,517			134,896			794,418	919,487
Income from continuing operations	(17,481)			(17,764)			17,581	18,007
Regulated operation | Operating Segments | Pipeline
Segment Reporting Information [Line Items]
Revenues	44,152			36,549			102,929	79,697
Income from continuing operations	14,810			11,450			47,054	29,029
Regulated operation | Intersegment eliminations
Segment Reporting Information [Line Items]
Revenues	(4,104)			(3,762)			(43,430)	(37,914)
Regulated operation | Intersegment eliminations | Electric
Segment Reporting Information [Line Items]
Revenues	(96)			(27)			(188)	(82)
Regulated operation | Intersegment eliminations | Natural gas distribution
Segment Reporting Information [Line Items]
Revenues	(104)			(69)			(209)	(208)
Regulated operation | Intersegment eliminations | Pipeline
Segment Reporting Information [Line Items]
Revenues	(3,904)			(3,666)			(43,033)	(37,624)
Nonregulated operation
Segment Reporting Information [Line Items]
Revenues	764,463			721,261			2,099,271	2,228,061
Income from continuing operations	40,538			63,590			101,307	208,803
Nonregulated operation | Operating Segments
Segment Reporting Information [Line Items]
Revenues	764,463			721,261			2,099,271	2,228,061
Nonregulated operation | Operating Segments | Pipeline
Segment Reporting Information [Line Items]
Revenues	3,476			3,855			9,542	9,389
Income from continuing operations	374			508			447	337
Nonregulated operation | Operating Segments | Construction services
Segment Reporting Information [Line Items]
Revenues	760,986			717,406			2,089,711	2,218,672
Income from continuing operations	41,767			35,975			108,953	105,951
Nonregulated operation | Operating Segments | Other
Segment Reporting Information [Line Items]
Revenues	1			0			18	0
Income from continuing operations	(1,603)			27,107			(8,093)	102,515
Nonregulated operation | Intersegment eliminations
Segment Reporting Information [Line Items]
Revenues	(1,459)			(1,724)			(4,864)	(6,677)
Nonregulated operation | Intersegment eliminations | Pipeline
Segment Reporting Information [Line Items]
Revenues	(27)			(35)			(263)	(265)
Nonregulated operation | Intersegment eliminations | Construction services
Segment Reporting Information [Line Items]
Revenues	0			0			(336)	0
Nonregulated operation | Intersegment eliminations | Other
Segment Reporting Information [Line Items]
Revenues	$ (1,432)			$ (1,689)			$ (4,265)	$ (6,412)

Business segment data - Sched_2

Business segment data - Schedule of Operating Revenues Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	$ 1,050,516	$ 1,000,795	$ 3,311,886	$ 3,522,020
Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	1,054,646	1,004,592	3,355,897	3,560,199
Corporate, Non-Segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	1,433	1,689	4,283	6,412
Intersegment eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	$ (5,563)	$ (5,486)	$ (48,294)	$ (44,591)

Employee benefit plans - Schedu

Employee benefit plans - Schedule of Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Pension benefits
Defined benefit plan disclosure, net periodic benefit cost [Line Items]
Interest cost	$ 3,200	$ 3,380	$ 9,600	$ 10,140
Expected return on assets	(4,028)	(4,299)	(12,084)	(12,897)
Amortization of net actuarial gain (loss)	1,037	773	3,111	2,319
Net periodic benefit cost (credit)	209	(146)	627	(438)
Other postretirement benefits
Defined benefit plan disclosure, net periodic benefit cost [Line Items]
Service cost	126	131	378	405
Interest cost	459	489	1,377	1,467
Expected return on assets	(1,329)	(1,334)	(3,987)	(4,026)
Amortization of prior service credit	(330)	(330)	(990)	(989)
Amortization of net actuarial gain (loss)	(72)	(96)	(216)	(408)
Net periodic benefit credit, including amount capitalized	(1,146)	(1,140)	(3,438)	(3,551)
Less amount capitalized	25	23	72	76
Net periodic benefit cost (credit)	$ (1,171)	$ (1,163)	$ (3,510)	$ (3,627)

Employee benefit plans - Narrat

Employee benefit plans - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Supplemental employee retirement plans
Defined benefit plan disclosure, net periodic benefit cost [Line Items]
Net periodic benefit cost (credit)	$ 733	$ 759	$ 2,200	$ 2,300

Regulatory matters - MTPSC (Det

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

Regulatory matters - NDPSC (Det

Regulatory matters - NDPSC (Details) - NDPSC - Montana-Dakota Utilities Co. $ in Millions	Nov. 01, 2024 USD ($)	Dec. 13, 2023 USD ($)	Nov. 01, 2023 USD ($)	Sep. 16, 2024 USD ($)
Public Utilities, General Disclosures [Line Items]
Public utilities, annual revenue increase (decrease)				$ 9.4
Public utilities, annual revenue increase (decrease), percentage				0.061
Natural gas distribution | Pending Rate Case
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 | Subsequent Event
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 - SDPUC (Det

Regulatory matters - SDPUC (Details) - SDPUC - Montana-Dakota Utilities Co. $ in Millions	Jan. 26, 2024 USD ($)	Aug. 15, 2023 USD ($)	Jul. 26, 2024 USD ($)
Public Utilities, General Disclosures [Line Items]
Public utilities, interim rate increase (decrease), amount	$ 2.7
Public utilities, interim rate increase (decrease), percentage	15.40%
Public utilities, annual revenue increase (decrease)			$ 1.4
Public utilities, annual revenue increase (decrease), percentage			0.086
Electric
Public Utilities, General Disclosures [Line Items]
Public utilities, requested rate increase (decrease), amount		$ 3
Public utilities, requested rate increase (decrease), percentage		17.30%
Natural gas distribution
Public Utilities, General Disclosures [Line Items]
Public utilities, requested rate increase (decrease), amount		$ 7.4
Public utilities, requested rate increase (decrease), percentage		11.20%
Public utilities, annual revenue increase (decrease)			$ 5.4
Public utilities, annual revenue increase (decrease), percentage			0.081

Regulatory matters - WUTC (Deta

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

Regulatory matters - WYPSC (Det

Regulatory matters - WYPSC (Details) - Natural gas distribution - WYPSC - Montana-Dakota Utilities Co. - Subsequent Event $ 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

Contingencies - Litigation (Det

Contingencies - Litigation (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023	Sep. 30, 2023
Commitments and Contingencies Disclosure [Abstract]
Potential liabilities related to litigation and environmental matters	$ 23,500	$ 22,500	$ 21,000
Loss contingency, receivable	1,500	202	98
Loss contingency, regulatory asset	$ 20,900	$ 21,600	$ 20,100

Contingencies - Guarantees (Det

Contingencies - Guarantees (Details)	Sep. 30, 2024 USD ($)
Commitments and Contingencies Disclosure [Abstract]
Guarantor obligations, maximum exposure, undiscounted	$ 557,500,000
Fixed maximum amounts guaranteed by year 2024	13,300,000
Fixed maximum amounts guaranteed by year 2025	186,700,000
Fixed maximum amounts guaranteed by year 2026	312,600,000
Fixed maximum amounts guaranteed by year 2027	43,500,000
Fixed maximum amounts guaranteed by year 2028	1,000,000
Fixed maximum amounts guaranteed, thereafter	400,000
Amount outstanding under guarantees that is reflected on balance sheet	0
Letters of credit	14,300,000
Letters of credit set to expire - 2024	12,300,000
Letters of credit set to expire - 2025	2,000,000
Outstanding letters of credit	0
Amount of surety bonds outstanding	$ 848,200,000

Contingencies - Variable Intere

Contingencies - Variable Interest Entities (Details) $ in Millions	Sep. 30, 2024 USD ($)
Fuel contract
Variable Interest Entities [Line Items]
Variable interest entity, reporting entity involvement, maximum loss exposure, amount	$ 26.1

Subsequent event (Details)

Subsequent event (Details) $ in Thousands			9 Months Ended
	Nov. 01, 2024 USD ($)	Oct. 31, 2024 USD ($)	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)	Dec. 31, 2023 USD ($)
Subsequent Events [Line Items]
Repayment of long-term debt			$ 147,731	$ 434,994
Long-term debt			$ 2,452,297	$ 2,341,147	$ 2,298,223
Subsequent Event | Term Loan Agreement
Subsequent Events [Line Items]
Repayment of long-term debt	$ 190,000
Long-term debt		$ 375,000
Subsequent Event | Discontinued Operations, Disposed of by Means Other than Sale, Spinoff | Everus
Subsequent Events [Line Items]
Stock split, conversion ratio		4