Income Taxes - Summary of Reconciliation of Income Tax Expense (Benefit) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Income tax benefit at statutory rate	$ (20,699)	$ (8,242)
State income tax, net of federal benefit	(6,823)	(3,783)
Permanent items	8	16
Stock-based compensation	215	56
Orphan drug credit	(2,544)	(925)
Research and development credits	(863)	(763)
Uncertain tax positions	785	548
Change in state rate	74	(34)
Change in valuation allowance	28,090	13,179
Other	1,757	(52)
Income tax expense (benefit)	$ 0	$ 0