Commitments and Contingencies - Additional Information (Detail) $ in Thousands		1 Months Ended			3 Months Ended		6 Months Ended
	Aug. 20, 2019 USD ($)	Oct. 31, 2020 USD ($)	Jun. 30, 2020 lease	Jul. 31, 2019 agreement	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($) lease	Jun. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)	Jan. 01, 2019 USD ($)
Other Commitments [Line Items]
Research and development expense					$ 25,225	$ 26,108	$ 44,356	$ 59,644
Operating lease liabilities					4,495		4,495
Operating lease right-of-use assets					$ 3,641		$ 3,641		$ 4,279
New Stamford Lease [Member]
Other Commitments [Line Items]
Number of renewable terms | lease			1
Operating Lease, renewable term			5 years			5 years		5 years
Operating lease, expiration date			Dec. 31, 2023
Operating lease liabilities		$ 1,934
Operating lease right-of-use assets		1,934
Lease incentives		$ 0
Stamford Operating Lease [Member]
Other Commitments [Line Items]
Number of renewable terms | lease							1
Operating Lease, renewable term					5 years		5 years
Operating lease, expiration date							Dec. 31, 2023
Deferred lease obligation										$ 864
Operating lease cost						$ 236		$ 470
Stamford Operating Lease [Member] | Research and Development [Member]
Other Commitments [Line Items]
Operating lease cost						165		329
Stamford Operating Lease [Member] | General and Administrative [Member]
Other Commitments [Line Items]
Operating lease cost						71		141
Stamford Operating Lease [Member] | ASC 842 [Member]
Other Commitments [Line Items]
Operating lease liabilities										5,198
Stamford Operating Lease [Member] | Standby Letter of Credit [Member]
Other Commitments [Line Items]
Letter of credit, renewal term							automatically renewed annually through November 2023.
Letter of credit, expiration date							Nov. 30, 2023
Stamford Operating Lease [Member] | Leasehold Improvements [Member]
Other Commitments [Line Items]
Tenant improvement expenses										$ 698
Stamford Operating Lease and New Stamford Lease [Member]
Other Commitments [Line Items]
Operating lease cost					$ 406		$ 812
Stamford Operating Lease and New Stamford Lease [Member] | Research and Development [Member]
Other Commitments [Line Items]
Operating lease cost					284		568
Stamford Operating Lease and New Stamford Lease [Member] | General and Administrative [Member]
Other Commitments [Line Items]
Operating lease cost					122		244
Non-Exclusive License Agreement | Enteris Biopharma, Inc. [Member]
Other Commitments [Line Items]
Upfront fee	$ 8,000
Upfront fee payment, cash	4,000
Upfront fee payment, stock	$ 4,000
Percentage of Payment, In Stock	50.00%
Payment of milestone payment					$ 10,000	0	$ 10,000	0
Payments for Royalties						$ 0		$ 0
MSA | Patheon and Patheon Manufacturing Services LLC [Member]
Other Commitments [Line Items]
Number of related product agreements | agreement				2