Leases - Additional Information (Detail) $ in Thousands		9 Months Ended
	Nov. 11, 2019 USD ($) ft²	Sep. 30, 2021 USD ($) m² ft²	Dec. 31, 2020 USD ($)
Lessee, Lease, Description [Line Items]
Operating lease, liability		$ 6,108
Right-of-use assets		$ 9,071	$ 7,960
Waltham Lease
Lessee, Lease, Description [Line Items]
Current office space under lease agreement | ft²		6,000
Operating lease expiration (years)		5 years
Current base rent		$ 263
Lease, term of contract (years)		5 years
Vienna Lease
Lessee, Lease, Description [Line Items]
Current office space under lease agreement | m²		400
Current base rent		$ 154
Lease, term of contract (years)		2 years
Office space | m²		1,200
Lease not yet commenced, term of contract		7 years
Building improvements		$ 709
Annual base rent		$ 300
Allston Lease
Lessee, Lease, Description [Line Items]
Current office space under lease agreement | ft²	28,000
Lease not yet commenced	$ 1,000
Lease, renewal term of contract (years)	5 years