Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement Of Income And Comprehensive Income [Abstract]
Net Income	$ 35,227	$ 76,598	$ 95,393
Other comprehensive loss, gross of tax:
Net gain (loss) on pension benefit obligations	244	(675)	847
Foreign currency translation adjustments	48,059	(16,678)	(25,904)
Unrealized gain (loss) on foreign currency derivative securities	301	(1,395)	10
Unrealized gain (loss) on commodity derivative securities	55	743	(725)
Other comprehensive loss, gross of tax	48,659	(18,005)	(25,772)
Other comprehensive loss, related tax effects:
Net gain (loss) on pension benefit obligations	(60)	185	(234)
Foreign currency translation adjustments	148	297	(417)
Unrealized gain (loss) on foreign currency derivative securities	(81)	375
Unrealized gain (loss) on commodity derivative securities	(19)	(273)	496
Other comprehensive loss, related tax effect	(12)	584	(155)
Other comprehensive loss, net of tax:	48,647	(17,421)	(25,927)
Comprehensive income:	$ 83,874	$ 59,177	$ 69,466