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	$ (21,573)	$ (11,917)	$ (56,759)	$ (29,450)
Other comprehensive income:
Unrealized gain on marketable securities	11	23	105	69
Total comprehensive loss	$ (21,562)	$ (11,894)	$ (56,654)	$ (29,381)