Condensed Consolidated Statements of Comprehensive Income (Loss) (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Statement Of Income And Comprehensive Income [Abstract]
Net income (loss)	$ 131,106	$ (16,832)
Other comprehensive income (loss), net of tax:
Net loss arising during the period, net of tax benefit of $0 and $6,817		(19,402)
Effect of pension settlement, net of tax benefit of $0 and $11,177		31,811
Amortization of prior service credit included in net income (loss), net of tax benefit of $73 and $76	(204)	(215)
Amortization of actuarial loss included in net income (loss), net of tax expense of $1,109 and $1,189	3,157	3,384
Cash flow hedges, net of tax expense (benefit) of $4,031 and $(1,810)	64,107	(38,525)
Other comprehensive income (loss), net of tax	67,060	(22,947)
Comprehensive income (loss)	$ 198,166	$ (39,779)