Comprehensive Income (Loss) - Components (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Accumulated Other Comprehensive Income (Loss):
Beginning balance			$ 85,580
Net other comprehensive income	$ (3,842)	$ 29,638	(16,067)	$ 55,722
Ending balance	78,546		78,546
Foreign currency translation adjustment:
Accumulated Other Comprehensive Income (Loss):
Beginning balance	(22,953)	(23,206)	(23,202)	(23,336)
Net other comprehensive income	(482)	117	(233)	247
Ending balance	(23,435)	(23,089)	(23,435)	(23,089)
Unrealized gain (loss) on marketable securities, net
Accumulated Other Comprehensive Income (Loss):
Beginning balance	(302)	(185)	(64)	(229)
Net other comprehensive income	78	594	(160)	638
Ending balance	(224)	409	(224)	409
Accumulated Other Comprehensive Income (Loss):
Accumulated Other Comprehensive Income (Loss):
Ending balance	$ (23,659)	$ (22,680)	$ (23,659)	$ (22,680)