Discontinued Operations and Disposal Groups (Details) - USD ($) $ in Thousands		3 Months Ended	9 Months Ended
	Apr. 25, 2023	Sep. 30, 2023	Sep. 30, 2023	Sep. 30, 2022	May 31, 2023	Dec. 31, 2022
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Discontinued Operations Pro Rata Distribution					90.00%
Retained Shares Ownership Percentage					10.00%
Long-term debt		$ 2,341,147	$ 2,341,147	$ 2,278,730		$ 2,365,667
Repayments of Long-term Debt			$ 434,994	0
Treasury Stock, Shares, Retired		538,921	538,921
Restructuring and Related Cost, Incurred Cost		$ 1,000	$ 47,100
Retained Shares [Abstract]					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		1,300	1,900
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		407	684
Knife River Corporation
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Repayments of Long-term Debt	$ 825,000
Senior Notes
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Long-term debt		$ 1,757,000	$ 1,757,000	$ 1,847,000		$ 1,848,500
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
Revolving Credit Facility | Knife River Corporation
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Long-term debt	350,000
Term Loan Agreement | Knife River Corporation
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Long-term debt	$ 275,000