Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net earnings	$ 34,571	$ 32,295	$ 25,938
Other comprehensive income :
Foreign currency translation adjustment	1,844	(328)	(847)
Pension and postretirement benefits, net of tax	(1,102)	1,473	(77)
Comprehensive income	$ 35,313	$ 33,440	$ 25,014