Comprehensive Income (Loss) - Components (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Accumulated Other Comprehensive Loss:
Beginning balance	$ 2,780	$ 85,580
Net other comprehensive income (loss)	(12,805)	(12,225)
Ending balance	(9,582)	87,054
Foreign currency translation adjustment:
Accumulated Other Comprehensive Loss:
Beginning balance	(23,621)	(23,202)
Net other comprehensive income (loss)	(161)	249
Ending balance	(23,782)	(22,953)
Unrealized gain (loss) on marketable securities, net
Accumulated Other Comprehensive Loss:
Beginning balance	205	(64)
Net other comprehensive income (loss)	374	(238)
Ending balance	579	(302)
Accumulated Other Comprehensive Loss:
Accumulated Other Comprehensive Loss:
Beginning balance	(23,416)	(23,266)
Ending balance	$ (23,203)	$ (23,255)