Subsequent Events - Additional Information (Details) - Collaborative Arrangement - USD ($)	Feb. 27, 2020	Dec. 31, 2019	Dec. 31, 2016	Jan. 31, 2016
Bristol Myers Squibb Company
Subsequent Event [Line Items]
Contingent milestone payments receivable			$ 15,000,000.0	$ 10,000,000.0
Immuno Gen Inc
Subsequent Event [Line Items]
Milestone payments payable		$ 0
Subsequent Event | Bristol Myers Squibb Company
Subsequent Event [Line Items]
Contingent milestone payments receivable	$ 10,000,000.0
Subsequent Event | Immuno Gen Inc
Subsequent Event [Line Items]
Milestone payments payable	$ 3,000,000.0