Condensed Consolidated Statements of Comprehensive Income (unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Condensed Consolidated Statements of Comprehensive Income (unaudited) [Abstract]
Net earnings	$ 19,679	$ 16,536	$ 39,025	$ 32,053
Other comprehensive income, net of tax:
Net foreign currency translation adjustment	(2,911)	2,697	(1,548)	3,238
Net change in postretirement benefit plans, net of taxes of $(0) and $(4) for the three months ended June 30, 2018 and 2017, and $(4) and $(9) for the six months ended June 30, 2018 and 2017.	16	11	29	21
Other comprehensive (loss)/income	(2,895)	2,708	(1,519)	3,259
Comprehensive income	$ 16,784	$ 19,244	$ 37,506	$ 35,312