Condensed Consolidated Statements of Comprehensive Income (unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Condensed Consolidated Statements of Comprehensive Income (unaudited) [Abstract]
Net earnings	$ 16,043	$ 14,012	$ 48,096	$ 40,048
Other comprehensive income, net of tax:
Net foreign currency translation adjustment	1,502	302	4,740	850
Net change in postretirement benefit plan, net of taxes of $(5) and $(4) for the three months ended September 30, 2017 and 2016, and $(14) and $(9) for the nine months ended September 30, 2017 and 2016.	10	9	31	(421)
Other comprehensive income	1,512	311	4,771	429
Comprehensive income	$ 17,555	$ 14,323	$ 52,867	$ 40,477