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		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Operating revenues	$ 0	$ 428,020	$ 0	$ 735,259
Operating expenses	161	416,686	161	767,960
Operating (loss) income	(161)	11,334	(161)	(32,701)
Other income	0	1,889	0	2,381
Interest expense	0	23,544	0	37,611
Loss from discontinued operations before income taxes	(161)	(10,321)	(161)	(67,931)
Income tax (benefit) expense	(23)	6,620	(23)	(5,467)
Discontinued operations, net of tax	$ (138)	$ (16,941)	$ (138)	$ (62,464)