CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement of Comprehensive Income [Abstract]
Foreign currency translation adjustments, deferred income taxes	$ (2,579)	$ 1,458	$ (952)	$ 1,851
Net gain (loss) on cash flow hedging instruments, deferred income taxes	(1,046)	611	(1,885)	867
Pension liability adjustments, deferred income taxes	(288)	(522)	(613)	(1,044)
Unrealized gain (loss) on marketable securities, deferred income taxes	$ 4	$ 0	$ 8	$ (3)