Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Operating expenses:
Research and development	$ 10,189	$ 11,728	$ 21,780	$ 21,865
General and administrative	6,260	3,479	10,804	6,844
Total operating expenses	16,449	15,207	32,584	28,709
Loss from operations	(16,449)	(15,207)	(32,584)	(28,709)
Other income (expense), net:
Changes in fair value of warrant liabilities			(16,240)
Other income (expense), net	(24)	348	517	673
Total other income (expense), net	(24)	348	(15,723)	673
Loss before provision for (benefit from) income taxes, net	(16,473)	(14,859)	(48,307)	(28,036)
Provision for (benefit from) income taxes, net	(11)	19	67	(126)
Net loss and comprehensive loss	$ (16,462)	$ (14,878)	$ (48,374)	$ (27,910)
Net loss per common share, basic and diluted	$ (1.58)	$ (7.97)	$ (4.71)	$ (14.97)
Weighted-average shares used in computing net loss per common share, basic and diluted	10,395,732	1,867,207	10,276,180	1,864,684