STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Income Statement [Abstract]
Collaboration revenue	$ 398	$ 0
Operating expenses:
Research and development	49,643	52,696
General and administrative	27,564	27,665
Property and equipment and right of use assets impairment	740	0
Total operating expenses	77,947	80,361
Loss from operations	(77,549)	(80,361)
Other income, net	(1,202)	385
Net loss	(78,751)	(79,976)
Net income (loss) applicable to common stockholders	$ (78,751)	$ (79,976)
Basic and diluted net loss per share	$ (0.37)	$ (0.38)
Weighted average common shares outstanding used to compute basic net income (loss) per share	214,399,074	209,636,456