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