Condensed Consolidated Statements of Comprehensive Income (unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Condensed Consolidated Statements of Comprehensive Income (unaudited) [Abstract]
Net earnings	$ 16,536	$ 14,150	$ 32,053	$ 26,036
Other comprehensive income (loss), net of tax:
Net foreign currency translation adjustment	2,697	(707)	3,238	548
Net change in postretirement benefit plan, net of taxes of $(4) and $(6) for the three months ended June 30, 2017 and 2016, and $(9) and $(5) for the six months ended June 30, 2017 and 2016.	11	(426)	21	(430)
Other comprehensive income (loss)	2,708	(1,133)	3,259	118
Comprehensive income	$ 19,244	$ 13,017	$ 35,312	$ 26,154