Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Consolidated Statements of Comprehensive Income [Abstract]
Net earnings	$ 90,071	$ 55,972	$ 59,722
Other comprehensive income/(loss), net of tax:
Net foreign currency translation adjustment	5,404	(1,390)	(2,615)
Net change in postretirement benefit plan, net of taxes of $207, $49, and $72 at December 31, 2017, 2016, and 2015, respectively	(197)	(345)	152
Other comprehensive income/(loss)	5,207	(1,735)	(2,463)
Comprehensive income	$ 95,278	$ 54,237	$ 57,259