Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Comprehensive Income [Abstract]
Net loss	$ (120,011)	$ (91,248)	$ (69,770)
Other comprehensive (loss) income :
Unrealized loss on available-for-sale securities, net of income tax expense of $0, $2.2 million and $0 for the years ended December 31, 2018, 2017, and 2016, respectively	0	16,039	4,185
Foreign currency translation adjustments	(2,490)	1,539	(445)
Other comprehensive (loss) income	(2,490)	17,578	3,740
Total comprehensive loss	$ (122,501)	$ (73,670)	$ (66,030)