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	$ (26,887)	$ (15,001)	$ (52,739)
Other comprehensive income (loss):
Unrealized gain (loss) on available-for-sale securities	9	(3)	2
Comprehensive loss	$ (26,878)	$ (15,004)	$ (52,737)