Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Income Statement [Abstract]
Revenue from collaboration agreements	$ 9,781	$ 9,670	$ 17,207	$ 16,486
Operating expenses:
Research and development	23,286	17,760	43,812	34,072
General and administrative	8,611	2,769	16,020	5,611
Total operating expenses	31,897	20,529	59,832	39,683
Loss from operations	(22,116)	(10,859)	(42,625)	(23,197)
Other (expense) income, net:
Interest expense and amortization of long-term debt − related party	(533)	(127)	(1,067)	(127)
Interest and other income, net	69	25	141	284
Total other (expense) income, net	(464)	(102)	(926)	157
Loss before income taxes	(22,580)	(10,961)	(43,551)	(23,040)
Income tax benefit		168		335
Net loss	(22,580)	(10,793)	(43,551)	(22,705)
Unrealized gain (loss) on marketable securities	25	(2)	(82)	(2)
Comprehensive loss	(22,555)	(10,795)	(43,633)	(22,707)
Reconciliation of net loss to net loss attributable to common stockholders:
Net loss	(22,580)	(10,793)	(43,551)	(22,705)
Accrual of preferred stock dividends		(2,908)		(5,019)
Net loss attributable to common stockholders	$ (22,580)	$ (13,701)	$ (43,551)	$ (27,724)
Net loss per share attributable to common stockholders − basic and diluted	$ (0.51)	$ (9.28)	$ (1.00)	$ (18.87)
Weighted-average number of shares used in computed net loss per share − basic and diluted	43,855,420	1,476,378	43,472,327	1,469,571