CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (18,166)	$ (15,972)	$ (35,029)	$ (25,432)
Other comprehensive (loss) income:
Unrealized (losses) gains on available-for-sale investments, net of taxes of $(205) and $4,552 for the three months ended June 30, 2016 and 2015, respectively, and $(2,263) and $4,552 for the six months ended June 30, 2016 and 2015, respectively	(389)	7,493	(4,311)	7,512
Comprehensive loss	$ (18,555)	$ (8,479)	$ (39,340)	$ (17,920)