Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Statement of Comprehensive Income [Abstract]
Net Income	$ 106,854	$ 19,573	$ 219,686	$ 105,771
Other comprehensive income, before tax:
Foreign currency translation adjustments	255	(273)	751	130
Recognition of previously deferred post-retirement benefit plan costs	1,353	1,604	2,578	3,102
Other comprehensive income, before tax	1,608	1,331	3,329	3,232
Income tax effect related to components of other comprehensive income	(414)	(335)	(857)	(814)
Total other comprehensive income	1,194	996	2,472	2,418
Comprehensive income	108,048	20,569	222,158	108,189
Comprehensive (income) loss attributable to redeemable noncontrolling interest	(227)	374	(442)	484
Total comprehensive income	$ 107,821	$ 20,943	$ 221,716	$ 108,673