CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE EARNINGS - UNAUDITED - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Statement Of Income And Comprehensive Income [Abstract]
Net (loss) earnings	$ (63,896)	$ 11,073	$ (51,031)	$ 19,738
Other comprehensive earnings (loss):
Changes in fair market value of derivatives, net of tax	(292)	909	100	(2,861)
Changes in unrealized pension cost, net of tax	72,530	1,239	90,976	3,733
Cumulative translation adjustment, net of tax	(10)	99	2	(54)
Other comprehensive earnings	72,228	2,247	91,078	818
Comprehensive earnings	$ 8,332	$ 13,320	$ 40,047	$ 20,556