Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (44,348)	$ (27,236)	$ (21,698)
Other comprehensive income (loss):
Unrealized gain (loss) on marketable securities	75	(98)	(3)
Total comprehensive loss	$ (44,273)	$ (27,334)	$ (21,701)