Condensed Consolidated Statements of Comprehensive Loss (Unaudited) - 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	$ (15,383)	$ (11,080)	$ (31,470)	$ (20,151)
Other comprehensive loss:
Unrealized gain (loss) on available-for-sale investments	38	(106)	190	(106)
Comprehensive loss	$ (15,345)	$ (11,186)	$ (31,280)	$ (20,257)