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	$ (18,033)	$ (21,573)	$ (58,179)	$ (56,759)
Other comprehensive income (loss):
Foreign currency translation adjustment	5		5
Unrealized (loss) gain on marketable securities	(24)	11	(36)	105
Total comprehensive loss	$ (18,052)	$ (21,562)	$ (58,210)	$ (56,654)