Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Operating revenues:
Revenues	$ 4,657,340	$ 4,441,784	$ 3,454,436
Operating expenses:
Total operation and maintenance	2,970,872	2,825,694	2,209,931
Purchased natural gas sold	742,965	757,883	483,118
Depreciation and amortization	213,598	210,028	198,240
Taxes, other than income	196,046	186,173	157,991
Electric fuel and purchased power	107,881	92,007	74,105
Operating expenses	4,231,362	4,071,785	3,123,385
Operating income	425,978	369,999	331,051
Realized gain on tax-free exchange of the retained shares in Knife River	186,556	0	0
Other income	41,672	11,228	25,724
Interest expense	114,308	80,698	70,709
Income before income taxes	539,898	300,529	286,066
Income taxes	59,473	49,761	43,544
Income from continuing operations	480,425	250,768	242,522
Discontinued operations, net of tax	(65,718)	116,721	135,609
Net income	$ 414,707	$ 367,489	$ 378,131
Earnings per share - basic:
Income from continuing operations (in usd per share)	$ 2.36	$ 1.23	$ 1.20
Discontinued operations, net of tax (in usd per share)	(0.32)	0.58	0.67
Earnings per share - basic (in usd per share)	2.04	1.81	1.87
Earnings per share - diluted:
Income from continuing operations (in usd per share)	2.36	1.23	1.20
Discontinued operations, net of tax (in usd per share)	(0.33)	0.58	0.67
Earnings per share - diluted (in usd per share)	$ 2.03	$ 1.81	$ 1.87
Weighted average common shares outstanding - basic (in shares)	203,640	203,358	202,076
Weighted average common shares outstanding - diluted (in shares)	203,938	203,462	202,383
Regulated Operation
Operating revenues:
Revenues	$ 1,789,637	$ 1,736,397	$ 1,390,992
Operating expenses:
Total operation and maintenance	397,037	375,347	367,234
Income from continuing operations	166,312	138,501	143,298
Nonregulated Operation
Operating revenues:
Revenues	2,867,703	2,705,387	2,063,444
Operating expenses:
Total operation and maintenance	2,573,835	2,450,347	1,842,697
Income from continuing operations	$ 314,113	$ 112,267	$ 99,224