Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Statement [Abstract]
Collaboration revenue	$ 100		$ 100
Operating expenses:
Research and development	10,432	$ 10,113	32,212	$ 31,978
General and administrative	4,112	3,151	14,916	9,995
Total operating expenses	14,544	13,264	47,128	41,973
Loss from operations	(14,444)	(13,264)	(47,028)	(41,973)
Other income (expense), net:
Changes in fair value of warrant liabilities			(16,240)
Other income (expense), net	(22)	288	495	961
Total other income (expense), net	(22)	288	(15,745)	961
Loss before provision for (benefit from) income taxes, net	(14,466)	(12,976)	(62,773)	(41,012)
Provision for (benefit from) income taxes, net	39	(73)	106	(199)
Net loss and comprehensive loss	$ (14,505)	$ (12,903)	$ (62,879)	$ (40,813)
Net loss per common share, basic and diluted	$ (1.39)	$ (6.91)	$ (6.09)	$ (21.88)
Weighted-average shares used in computing net loss per common share, basic and diluted	10,441,384	1,867,176	10,331,650	1,865,503