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	$ 7,914	$ 21,554	$ 64,575
Foreign currency translation adjustments	58,609	(27,407)	(38,817)
Net change in:
Deferred gains (losses) on cash flow hedges, net of taxes of $1,930, $(335) and $880, respectively	(5,592)	1,725	(2,581)
Unrecognized retirement obligations, net of taxes of $(6,293), $(7,247) and $(2,920), respectively	10,914	11,562	5,782
Other comprehensive income (loss)	63,931	(14,120)	(35,616)
Comprehensive income	$ 71,845	$ 7,434	$ 28,959