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	$ (15,437)	$ (21,013)	$ (21,761)
Change in unrealized gain (loss) on available-for-sale- securities, net of tax	(8)	13	(37)
Other comprehensive income (loss)	(8)	13	(37)
Comprehensive loss, net of income tax	$ (15,445)	$ (21,000)	$ (21,798)