CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Income Statement [Abstract]
Collaboration revenue	$ 7,917	$ 10,888
Operating expenses:
Research and development	20,214	12,960
General and administrative	12,171	6,379
Total operating expenses	32,385	19,339
Loss from operations	(24,468)	(8,451)
Investment and other income, net	157	61
Gain on extinguishment	2,318	0
Interest expense	(2,096)	(1,090)
Change in fair value of derivative liability	(11)	0
Change in fair value of warrant liability	223	244
Net loss	(23,877)	(9,236)
Reduction (accretion) of redeemable convertible preferred stock to redemption value	10,274	(5,936)
Net loss attributable to common stockholders	$ (13,603)	$ (15,172)
Net loss per share attributable to common stockholders, basic and diluted (in usd per share)	$ (4.50)	$ (25.85)
Weighted-average shares used to compute net loss per share attributable to common stockholders, basic and diluted (in shares)	3,023,023	586,969