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)