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	$ (12,706)	$ (7,694)	$ (41,568)	$ (19,218)
Other comprehensive income (loss):
Unrealized (loss) gain on available-for-sale securities	(26)	(28)	35	(24)
Total comprehensive loss	$ (12,732)	$ (7,722)	$ (41,533)	$ (19,242)