STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Statement [Abstract]
Collaboration revenue	$ 398		$ 398
Operating expenses:
Research and development	14,521	$ 13,968	41,427	$ 38,725
General and administrative	8,173	6,353	25,469	18,862
Total operating expenses	22,694	20,321	66,896	57,587
Loss from operations	(22,296)	(20,321)	(66,498)	(57,587)
Other income (expense):
Interest income (expense), net	(444)	7	(444)	412
Other income (expense), net	7	(1)	(15)	(29)
Other income (expense), net	(437)	6	(459)	383
Net loss	$ (22,733)	$ (20,315)	$ (66,957)	$ (57,204)
Basic and diluted net loss per share	$ (0.11)	$ (0.10)	$ (0.31)	$ (0.27)
Weighted average common shares outstanding, basic and diluted	214,542,465	212,837,367	214,310,349	208,497,410