Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net loss	$ (61,335)	$ (66,837)	$ (85,516)
Other comprehensive income, net of tax:
Foreign currency translation adjustment	(3,795)	3,748	686
Net change in unrealized (losses) gains on investments	(434)	88	(247)
Other comprehensive (loss) income, net of tax	(4,229)	3,836	439
Total comprehensive loss	$ (65,564)	$ (63,001)	$ (85,077)