CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS (unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (19,486)	$ (19,793)	$ (53,908)	$ (55,709)
Other comprehensive gain (loss):
Unrealized holding gain (loss) on marketable securities		17	(24)	24
Comprehensive loss	$ (19,486)	$ (19,776)	$ (53,932)	$ (55,685)