Discontinued operations - Narrative (Details) $ in Thousands				3 Months Ended		6 Months Ended
	May 31, 2024 shares	May 31, 2023 shares	Apr. 25, 2023 USD ($)	Jun. 30, 2024 USD ($)	Jun. 30, 2023 USD ($)	Jun. 30, 2024 USD ($)	Jun. 30, 2023 USD ($)	Dec. 31, 2023 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Long-term debt				$ 2,400,617	$ 2,247,422	$ 2,400,617	$ 2,247,422	$ 2,298,223
Repayment of long-term debt						11,127	506,191
Treasury stock retired (in shares) | shares	538,921
Separation related costs				138	41,200	138	46,100
Discontinued Operations, Disposed of by Means Other than Sale, Spinoff | Knife River Corporation
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Pro rata distribution of shares, percentage		0.90
Stock split, conversion ratio		4
Retained ownership percentage		0.10
Number of retained shares (in shares) | shares		5,700,000
Discontinued Operations, Disposed of by Means Other than Sale, Spinoff | Knife River Corporation | Cash Received, TSA
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Discontinued operation, amount of continuing cash flows after disposal				437	599	1,500	599
Discontinued Operations, Disposed of by Means Other than Sale, Spinoff | Knife River Corporation | Cash Paid, TSA
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Discontinued operation, amount of continuing cash flows after disposal				$ 62	$ 277	$ 140	$ 277
Knife River Corporation
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Repayment of long-term debt			$ 825,000
Knife River Corporation | Revolving Credit Facility
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Line of credit facility, maximum borrowing capacity			350,000
Knife River Corporation | Term Loan Agreement
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Debt instrument, face amount			275,000
Senior Notes | Knife River Corporation
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Long-term debt			$ 425,000