CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE EARNINGS - UNAUDITED - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Statement Of Income And Comprehensive Income [Abstract]
Net earnings	$ 875	$ 4,857	$ 12,865	$ 8,665
Other comprehensive earnings (loss):
Changes in fair market value of derivatives, net of tax	268	644	392	(3,770)
Changes in unrealized pension cost, net of tax	17,024	1,209	18,446	2,494
Cumulative translation adjustment, net of tax	1	(14)	13	(153)
Other comprehensive earnings (loss)	17,293	1,839	18,851	(1,429)
Comprehensive earnings	$ 18,168	$ 6,696	$ 31,716	$ 7,236