Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (14,013)	$ (9,245)	$ (12,126)	$ (5,319)	$ (4,319)	$ (7,545)	$ (6,981)	$ (7,572)	$ (40,703)	$ (26,417)	$ (26,624)
Change in unrealized gain (loss) on available-for-sale securities, net of tax									25	(37)	(14)
Comprehensive loss									$ (40,678)	$ (26,454)	$ (26,638)