Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating expenses:
Research and development	$ 41,078	$ 30,157	$ 33,895
General and administrative	14,339	12,462	14,180
Total operating expenses	55,417	42,619	48,075
Loss from operations	(55,417)	(42,619)	(48,075)
Other income, net	1,780	760	351
Loss before provision for (benefit from) income taxes, net	(53,637)	(41,859)	(47,724)
Provision for (benefit from) income taxes, net	(302)	156	143
Net loss and comprehensive loss	$ (53,335)	$ (42,015)	$ (47,867)
Net loss per common share, basic and diluted	$ (0.75)	$ (0.84)	$ (1.58)
Weighted-average shares used in computing net loss per common share, basic and diluted	70,739,210	49,899,299	30,240,258