Condensed Consolidated Statements of Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (6,238)	$ (3,413)	$ (16,215)	$ (7,308)
Other comprehensive income:
Unrealized gain on marketable securities	2	2	4	2
Total comprehensive loss	$ (6,236)	$ (3,411)	$ (16,211)	$ (7,306)