Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($)	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Income Statement [Abstract]
Revenue from collaboration agreements	$ 7,654,000	$ 7,426,000
Operating expenses:
Research and development	26,203,000	20,526,000
General and administrative	12,820,000	7,409,000
Total operating expenses	39,023,000	27,935,000
Loss from operations	(31,369,000)	(20,509,000)
Other (expense) income, net:
Interest expense and amortization of long-term debt − related party	(527,000)	(534,000)
Interest and other income, net	276,000	72,000
Total other (expense) income, net	(251,000)	(462,000)
Loss before income taxes	(31,620,000)	(20,971,000)
Income tax benefit	0	0
Net loss	$ (31,620,000)	$ (20,971,000)
Net loss per share attributable to common stockholders − basic and diluted	$ (0.65)	$ (0.49)
Weighted-average number of shares used in computed net loss per share − basic and diluted	48,734,827	43,084,978
Other comprehensive income (loss)
Unrealized gain (loss) on marketable securities	$ (2,875,000)	$ (107,000)
Comprehensive loss	$ (34,495,000)	$ (21,078,000)