Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (32,644)	$ (21,712)	$ (12,377)
Other comprehensive loss:
Net unrealized loss on available-for-sale securities	(69)
Total comprehensive loss	$ (32,713)	$ (21,712)	$ (12,377)