Comprehensive Income (Loss) - Components (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Accumulated Other Comprehensive Income (Loss):
Beginning balance			$ 85,580
Net other comprehensive income (loss)	$ (15,763)	$ 20,938	(31,830)	$ 76,660
Ending balance	65,742		65,742
Foreign currency translation adjustment:
Accumulated Other Comprehensive Income (Loss):
Beginning balance	(23,435)	(23,089)	(23,202)	(23,336)
Net other comprehensive income (loss)	(60)	(229)	(293)	18
Ending balance	(23,495)	(23,318)	(23,495)	(23,318)
Unrealized gain (loss) on marketable securities, net
Accumulated Other Comprehensive Income (Loss):
Beginning balance	(224)	409	(64)	(229)
Net other comprehensive income (loss)	68	(512)	(92)	126
Ending balance	(156)	(103)	(156)	(103)
Accumulated Other Comprehensive Income (Loss):
Accumulated Other Comprehensive Income (Loss):
Ending balance	$ (23,651)	$ (23,421)	$ (23,651)	$ (23,421)