Commitments and Contingencies - Additional Information (Details) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Jun. 30, 2018 ft²	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Dec. 31, 2020 ft²
Loss Contingencies [Line Items]
Rent expense | $		$ 420	$ 161	$ 773	$ 516
Plymouth Meeting, PA
Loss Contingencies [Line Items]
Operating lease square feet of office space | ft²	15,000					13,000
Operating lease expiration month and year	2024-05					2024-05