Comprehensive Income (Loss) - Components (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Accumulated Other Comprehensive Income (Loss):
Beginning balance	$ 85,580
Net other comprehensive income	(12,225)	$ 26,084
Ending balance	87,054
Foreign currency translation adjustment:
Accumulated Other Comprehensive Income (Loss):
Beginning balance	(23,202)	(23,336)
Net other comprehensive income	249	130
Ending balance	(22,953)	(23,206)
Unrealized gain (loss) on marketable securities, net
Accumulated Other Comprehensive Income (Loss):
Beginning balance	(64)	(229)
Net other comprehensive income	(238)	44
Ending balance	(302)	(185)
Accumulated Other Comprehensive Income (Loss):
Accumulated Other Comprehensive Income (Loss):
Ending balance	$ (23,255)	$ (23,391)