CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (4,081)	$ (7,070)	$ (15,307)	$ (29,244)
Other comprehensive income, net of tax:
Unrealized gain on investments	2	19	45	19
Total other comprehensive income	2	19	45	19
Comprehensive loss	$ (4,079)	$ (7,051)	$ (15,262)	$ (29,225)