Leases - Additional Information (Detail) $ in Thousands	1 Months Ended		6 Months Ended
	Apr. 30, 2019	Oct. 31, 2014 USD ($)	Jun. 30, 2020 USD ($) ft² USD_per_sqft	Dec. 31, 2019 USD ($)
Lessee Lease Description [Line Items]
Operating lease right-of-use assets			$ 23,469	$ 19,137
130 Brookline Street [Member]
Lessee Lease Description [Line Items]
Operating lease, description			In October 2014, the Company entered into an agreement to lease office and laboratory space at 130 Brookline Street (the “130 Brookline Lease”) in Cambridge, Massachusetts under an operating lease agreement with a term through January 2020, with an option to extend the term of the lease for an additional five-year period. In April 2019, the Company executed an amendment to the lease to extend the term of the lease for the additional five-year period, through January 2025.
Operating lease expiration		2020-01
Lessee operating lease extended expiration date	Jan. 31, 2025
Operating lease, existence of option to extend		true
Operating lease, options to extend			option to extend the term of the lease for an additional five-year period. In April 2019, the Company executed an amendment to the lease to extend the term of the lease for the additional five-year period, through January 2025.
Operating lease, renewal term	5 years	5 years
130 Brookline Street [Member] | Second Amendment [Member]
Lessee Lease Description [Line Items]
Operating lease, description			In March 2020, the Company entered into a second amendment to the 130 Brookline Lease (the “Second Amendment”). The Second Amendment amends certain terms of the Company’s existing lease, dated October 21, 2014, as amended on April 5, 2019. The Second Amendment extends the term of the 130 Brookline Lease by approximately six years through January 31, 2031.
Lessee operating lease extended expiration date			Jan. 31, 2031
Operating lease, existence of option to extend			true
Operating lease, options to extend			an option to extend the lease for two consecutive five-year terms
Operating lease, renewal term			6 years
Operating lease right-of-use assets			$ 7,300
Operating lease, liability			$ 7,300
130 Brookline Street [Member] | Other Assets [Member]
Lessee Lease Description [Line Items]
Lease security deposit		$ 300
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 281 Albany Lease is expected to commence on October 1, 2020, and 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”).
Expected commencement date			Oct. 01, 2020
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
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