Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Statement of Comprehensive Income [Abstract]
Net Income	$ 128,699	$ 132,270	$ 348,385	$ 238,041
Other comprehensive income, before tax:
Foreign currency translation adjustments	(53)	(93)	698	37
Recognition of previously deferred post-retirement benefit plan costs	1,290	1,551	3,869	4,653
Pension payment timing related charge	946	0	946	0
Pension and other postretirement benefit items	2,236	1,551	4,815	4,653
Unrealized gain on available-for-sale investment during the period	54,354	0	54,354	0
Other comprehensive income, before tax	56,537	1,458	59,867	4,690
Income tax effect related to components of other comprehensive income	(14,626)	(366)	(15,484)	(1,180)
Other comprehensive income, net of tax	41,911	1,092	44,383	3,510
Comprehensive income	170,610	133,362	392,768	241,551
Comprehensive (income) loss attributable to redeemable noncontrolling interest	(419)	(51)	(861)	433
Total comprehensive income	$ 170,191	$ 133,311	$ 391,907	$ 241,984