CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Statement of Comprehensive Income [Abstract]
Net income	$ 478,197	$ 482,763	$ 286,235
Other comprehensive (loss) income, before tax:
Foreign currency translation adjustments	743	138	(774)
Pension and other post-retirement benefit items:
Recognition of previously deferred post-retirement benefit plan costs	5,217	6,209	5,764
Actuarial gain (loss) arising during the period	4,463	22,574	(13,822)
Pension payment timing related charge	946	0	686
Pension and other postretirement benefit items	10,626	28,783	(7,372)
Unrealized gain on available-for-sale investment during the period	20,800	0	0
Other comprehensive income (loss), before tax	32,169	28,921	(8,146)
Income tax effect related to components of other comprehensive income (loss)	(8,309)	(7,400)	2,060
Other comprehensive income (loss), net of tax	23,860	21,521	(6,086)
Comprehensive income	502,057	504,284	280,149
Comprehensive loss attributable to redeemable non-controlling interest	(1,242)	15	0
Total comprehensive income	$ 500,815	$ 504,299	$ 280,149