Condensed Consolidated Statements of Comprehensive Income (unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Condensed Consolidated Statements of Comprehensive Income (unaudited) [Abstract]
Net earnings	$ 19,346	$ 15,518
Other comprehensive income, net of tax:
Net foreign currency translation adjustment	1,363	541
Net change in postretirement benefit plan, net of taxes of $(4) and $(5) for the three months ended March 31, 2018 and 2017	13	10
Other comprehensive income	1,376	551
Comprehensive income	$ 20,722	$ 16,069