Condensed Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (2,854)	$ (3,988)	$ (8,691)	$ (5,669)
Change in unrealized gain (loss) on available-for-sale-securities, net of tax		(1)	12	29
Other comprehensive income (loss)	0	(1)	12	29
Comprehensive loss, net of income tax	$ (2,854)	$ (3,989)	$ (8,679)	$ (5,640)