Significant Accounting Policies - Earnings Per Share (Details) - $ / shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average common shares outstanding - basic (in shares)	203,640,000	203,358,000	202,076,000
Effect of dilutive performance share awards (in shares)	298,000	104,000	307,000
Weighted average common shares outstanding - diluted (in shares)	203,938,000	203,462,000	202,383,000
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
Shares excluded from the calculation of diluted earnings per share (in shares)	0	14,000	0
Dividends declared per common share (in usd per share)	$ 0.6950	$ 0.8750	$ 0.8550
Discontinued Operations, Disposed of by Means Other than Sale, Spinoff | Knife River Corporation
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Treasury stock, retired (in shares)	538,921