CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE EARNINGS - UNAUDITED - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Statement Of Income And Comprehensive Income [Abstract]
Net earnings	$ 11,073	$ 2,722	$ 19,738	$ 26,084
Other comprehensive earnings:
Changes in fair market value of derivatives, net of tax	909	(740)	(2,861)	(956)
Changes in unrealized pension cost, net of tax	1,239	1,017	3,733	3,065
Cumulative translation adjustment, net of tax	99	(92)	(54)	(88)
Other comprehensive earnings	2,247	185	818	2,021
Comprehensive earnings	$ 13,320	$ 2,907	$ 20,556	$ 28,105