Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Operating expenses:
Research and development	$ 8,785	$ 7,194	$ 17,119	$ 15,202
General and administrative	4,178	3,283	7,598	6,429
Total operating expenses	12,963	10,477	24,717	21,631
Loss from operations	(12,963)	(10,477)	(24,717)	(21,631)
Other income	582	185	854	281
Loss before provision for (benefit from) income taxes, net	(12,381)	(10,292)	(23,863)	(21,350)
Provision for (benefit from) income taxes, net	(421)	37	(378)	71
Net loss	$ (11,960)	$ (10,329)	$ (23,485)	$ (21,421)
Net loss per common share, basic and diluted	$ (0.16)	$ (0.20)	$ (0.35)	$ (0.45)
Weighted-average shares used in computing net loss per common share, basic and diluted	74,320,415	52,268,443	67,061,904	47,459,428