Consolidated Statements of Comprehensive Earnings - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net earnings	$ 34,686	$ 36,146	$ 46,532
Other comprehensive (loss) earnings:
Changes in fair market value of derivatives, net of tax	(1,307)	(509)	795
Changes in unrealized pension cost, net of tax	(2,965)	6,439	(1,830)
Cumulative translation adjustment, net of tax	77	83	(311)
Other comprehensive (loss) earnings	(4,195)	6,013	(1,346)
Comprehensive earnings	$ 30,491	$ 42,159	$ 45,186