Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 44,315	$ 40,045	$ 43,209
Other comprehensive income (loss):
Foreign currency translation adjustment	16,966	(13,156)	(20,112)
Net gain (loss) on pension and other post-retirement benefits	987	2,369	544
Other comprehensive income (loss) before income tax (benefit) expense	17,953	(10,787)	(19,568)
Income tax (expense) benefit related to items of other comprehensive (loss) income	(363)	(890)	(152)
Other comprehensive income (loss)	17,590	(11,677)	(19,720)
Comprehensive income	$ 61,905	$ 28,368	$ 23,489