CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Statement [Abstract]
Collaboration revenue	$ 607	$ 2,573	$ 1,653	$ 6,065
Operating expenses:
Research and development	2,712	4,229	5,376	10,248
General and administrative	3,021	1,323	5,502	3,389
Total operating expenses	5,733	5,552	10,878	13,637
Loss from operations	(5,126)	(2,979)	(9,225)	(7,572)
Investment and other income, net	7	4	3	10
Interest expense	0	(660)	0	(884)
Change in fair value of derivative liability	0	11	0	11
Change in fair value of warrant liability	0	(8)	0	223
Net loss	(5,119)	(3,654)	(9,222)	(8,234)
Reduction (accretion) of redeemable convertible preferred stock to redemption value	0	(163)	0	10,356
Net income (loss) attributable to common stockholders	$ (5,119)	$ (3,817)	$ (9,222)	$ 2,122
Net loss per common share share attributable to common stockholders, basic (in usd per share)	$ (0.43)	$ (6.48)	$ (0.87)	$ 3.60
Net income (loss) per common share attributable to common stockholders, diluted (in usd per share)	$ (0.43)	$ (6.48)	$ (0.87)	$ (4.46)
Weighted-average shares used to compute net loss per share attributable to common stockholders, basic (in shares)	11,819,152	589,001	10,595,960	589,001
Weighted-average shares used to compute net income (loss) per share attributable to common stockholders, diluted (in shares)	11,819,152	589,001	10,595,960	1,845,467