Condensed Consolidated Statements of Comprehensive Income (unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Condensed Consolidated Statements of Comprehensive Income (unaudited) [Abstract]
Net earnings	$ 14,012	$ 13,976	$ 40,048	$ 44,063
Other comprehensive income (loss), net of tax:
Net foreign currency translation adjustment	302	375	850	(1,754)
Net change in postretirement benefit plan, net of taxes of $(4) and $1 for the three months ended September 30, 2016 and 2015, and $(9) and $5 for the nine months ended September 30, 2016 and 2015.	9	(3)	(421)	(9)
Other comprehensive income (loss)	311	372	429	(1,763)
Comprehensive income	$ 14,323	$ 14,348	$ 40,477	$ 42,300