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