CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (62,906)	$ (55,868)	$ (38,755)
Other comprehensive (loss) income:
Unrealized (losses) gains on available-for-sale investments, net of taxes of zero, $3,825 and zero for 2016, 2015, and 2014, respectively	(7,186)	7,320	(38)
Comprehensive loss	$ (70,092)	$ (48,548)	$ (38,793)