Condensed Consolidated Statements of Operations and Comprehensive Income (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	$ 1,913	$ 289	$ 3,692	$ 856
Operating expenses:
Research and development	6,156	9,532	18,130	30,048
General and administrative	2,728	2,467	7,850	7,365
Total operating expenses	8,884	11,999	25,980	37,413
Loss from operations	(6,971)	(11,710)	(22,288)	(36,557)
Other income (expense):
Interest expense	(214)	(66)	(560)	(197)
Interest income	11	301	202	1,042
Other income	1,037	0	1,042	0
Loss before taxes	(6,137)	(11,475)	(21,604)	(35,712)
Income tax benefit	0	0	6	0
Net loss	(6,137)	(11,475)	(21,598)	(35,712)
Comprehensive income (loss):
Unrealized gain (loss) on investments	0	5	(16)	37
Unrealized gain (loss) on foreign currency translation	14	(7)	(35)	(17)
Comprehensive loss	$ (6,123)	$ (11,477)	$ (21,649)	$ (35,692)
Weighted-average shares used to compute basic and diluted net loss per share (in shares)	22,277,146	18,586,950	19,826,985	18,281,707
Basic and diluted net loss per share (in dollars per share)	$ (0.28)	$ (0.62)	$ (1.09)	$ (1.95)