Condensed Consolidated Statements of Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (6,247)	$ (4,547)
Other comprehensive income (loss):
Unrealized gain (loss) on marketable securities	(33)	4
Total comprehensive loss	$ (6,280)	$ (4,543)