Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net Income	$ 19,007	$ 15,384	$ 28,008	$ 25,710
Other Comprehensive income:
Foreign currency translation adjustment	(16,248)	10,275	(8,518)	13,827
Reclassification adjustment from loss on partial settlement of pension plan, net of tax	0	0	3,815	0
Change in defined benefit pension plans, net of tax	0	0	577	0
Change in fair value of derivative financial instruments	748	(161)	1,078	657
Other comprehensive income:	(15,500)	10,114	(3,048)	14,484
Comprehensive income	$ 3,507	$ 25,498	$ 24,960	$ 40,194