Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (16,945)	$ (14,762)
Other comprehensive income (loss):
Unrealized (loss) gain on available-for-sale securities	(2)	1
Total comprehensive loss	$ (16,947)	$ (14,761)