Leases - Additional Information (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2021 USD ($) ft² USD_per_sqft	Dec. 31, 2020 USD ($)
Lessee Lease Description [Line Items]
Operating lease right-of-use assets	$ 77,912	$ 39,114
Albany Lease [Member]
Lessee Lease Description [Line Items]
Area of space leased | ft²	39,000
Operating lease, description	In March 2020, the Company entered into an agreement to lease approximately 39,000 square feet of office and laboratory space at 281 Albany Street in Cambridge, Massachusetts under an operating lease agreement (the “281 Albany Lease”). The Company’s obligation to pay rent will start on the date that is six months after the commencement date or the date on which the Company occupies the premises, whichever occurs earlier (the “Rent Commencement Date”).
Term of lease	10 years
Base rent per square foot for first year | USD_per_sqft	99.00
Base rent per square foot for last year | USD_per_sqft	128.87
Operating lease right-of-use assets	$ 40,400
Operating lease, liability	$ 34,800
Incremental borrowing rate	5.52%
Prepaid lease payments	$ 5,600
Amount receivable on cost of construction and tenant improvement	$ 4,400
Operating lease, existence of option to extend	true
Operating lease, options to extend	The Company has the option to extend the 281 Albany Lease for two successive five-year terms.
Albany Lease [Member] | Other Assets [Member]
Lessee Lease Description [Line Items]
Letter of credit	$ 1,900