Condensed Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Statement [Abstract]
Revenue	$ 0	$ 0	$ 0	$ 0
Operating expenses
Research and development	6,640	6,533	13,256	12,339
General and administrative	2,767	2,272	5,638	4,532
Total operating expenses	9,407	8,805	18,894	16,871
Loss from operations	(9,407)	(8,805)	(18,894)	(16,871)
Other income (expense)
Interest income	82	79	162	94
Interest expense	(35)	(112)	(76)	(268)
Other income, net	0	2	22	3
Loss before provision for income taxes	(9,360)	(8,836)	(18,786)	(17,042)
Provision for income taxes	0	0	0	0
Net loss	(9,360)	(8,836)	(18,786)	(17,042)
Unrealized gain (loss) on marketable securities, net of tax	(1)	0	5	0
Comprehensive loss	$ (9,361)	$ (8,836)	$ (18,781)	$ (17,042)
Net loss per common share – basic and diluted (in USD per share)	$ (0.55)	$ (0.75)	$ (1.30)	$ (2.47)
Weighted-average shares used in computing net loss per common share – basic and diluted (in shares)	16,868,643	11,753,259	14,434,365	6,890,166