CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Foreign currency translation adjustments, deferred income taxes	$ 3,471	$ (13,670)	$ (2,314)
Net gains (losses) on cash flow hedging instruments, deferred income taxes	(759)	(544)	(975)
Pension liability adjustments, deferred income taxes	(4,084)	34	1,443
Unrealized gain (loss) on marketable securities, deferred income taxes	$ (12)	$ (16)	$ 10