CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Statement of Comprehensive Income [Abstract]
Net income	$ 476,347	$ 631,198	$ 478,197
Other comprehensive income (loss) before tax:
Foreign currency translation adjustments	0	142	743
Pension and other post-retirement benefit items:
Recognition of previously deferred post-retirement benefit plan costs	5,590	4,158	5,217
Actuarial gain (loss) arising during the period	2,387	(21,892)	4,463
Pension payment timing related charge	0	300	946
Pension and other postretirement benefit items	7,977	(17,434)	10,626
Realized gain on available-for-sale investment during the period	0	(20,800)	0
Unrealized gain on available-for-sale investment during the period	0	0	20,800
Other comprehensive income (loss), before tax	7,977	(38,092)	32,169
Income tax effect related to components of other comprehensive income (loss)	(2,054)	9,775	(8,309)
Other comprehensive income (loss), net of tax	5,923	(28,317)	23,860
Comprehensive income	482,270	602,881	502,057
Comprehensive loss (income) attributable to redeemable non-controlling interest	377	(729)	(1,242)
Total comprehensive income	$ 482,647	$ 602,152	$ 500,815