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	$ (31,553)	$ (41,007)	$ (32,872)
Other comprehensive loss
Unrealized loss on available-for-sale securities	(94)	(2)	(11)
Total comprehensive loss	$ (31,647)	$ (41,009)	$ (32,883)