Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Income Statement [Abstract]
Revenue from collaboration agreements	$ 7,426	$ 6,816
Operating expenses:
Research and development	20,526	16,312
General and administrative	7,409	2,842
Total operating expenses	27,935	19,154
Loss from operations	(20,509)	(12,338)
Other (expense) income, net:
Interest expense and amortization of long-term debt − related party	(534)
Interest and other income, net	72	259
Total other (expense) income, net	(462)	259
Loss before income taxes	(20,971)	(12,079)
Income tax benefit		167
Net loss	(20,971)	(11,912)
Unrealized loss on marketable securities	(107)
Comprehensive loss	(21,078)	(11,912)
Reconciliation of net loss to net loss attributable to common stockholders:
Net loss	(20,971)	(11,912)
Accrual of preferred stock dividends		(2,111)
Net loss attributable to common stockholders	$ (20,971)	$ (14,023)
Net loss per share attributable to common stockholders − basic and diluted	$ (0.49)	$ (9.59)
Weighted-average number of shares used in computed net loss per share − basic and diluted	43,084,978	1,462,759