Leases - Additional Information (Detail)				1 Months Ended		3 Months Ended	12 Months Ended
	Dec. 16, 2019 USD ($) ft² Option	Jan. 01, 2019 USD ($)	Jan. 17, 2018 USD ($) ft²	Jul. 31, 2016 USD ($)	Aug. 31, 2015 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Lessee Lease Description [Line Items]
Lease payments							$ 1,234,000
Lease not yet commenced, total future minimum lease payments							$ 4,300,000
Lease not yet commenced, expected to commence, year and month							2020-06
Lease not yet commenced, term of contract							7 years
Rent expense								$ 800,000
Meiji License Agreement [Member]
Lessee Lease Description [Line Items]
Embedded finance leases fixed assets related payments						$ 1,600,000
Finance lease liability							$ 0
Office Space [Member]
Lessee Lease Description [Line Items]
Operating lease beginning date					2016-01
Operating lease expiration date					2020-12
Operating lease, existence of option to extend					true
Security deposit					$ 200,000
Annual rent escalations and tenant incentives					700,000
Amount reimbursed					$ 300,000
Operating lease decrease in right of use assets		$ 200,000
Office Space [Member] | Lease Agreements [Member] | Cambridge, Massachusetts [Member] | U.S. REIF Central Plaza Massachusetts, LLC [Member]
Lessee Lease Description [Line Items]
Operating lease beginning date	2020-06
Operating lease expiration date	2027-05
Operating lease, existence of option to extend	true
Operating lease decrease in right of use assets		$ 400,000
Area of office space | ft²	7,800		7,800
Term of lease			7 years
Lease expiration term			2025-12
Leasehold improvements receivable from the Landlord	$ 400,000		$ 400,000
Lease expiration date	May 31, 2027
Number of renewal options | Option	2
Lease renewal term	5 years
Operating lease, option to extend							the Company has two consecutive options to extend the Lease Term for an additional period of five years (the “Option Terms”), subject to certain conditions, upon notice to the Landlord.
Operating leases annual base rent initial	$ 600,000
Operating leases annual base rent final	$ 700,000
Operating lease percentage of annual base rent	100.00%
Laboratory Space [Member]
Lessee Lease Description [Line Items]
Lease expiration date							Nov. 30, 2019
Lease payments				$ 300,000