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Leases - Additional Information (Detail)
$ in Thousands
1 Months Ended
Jan. 31, 2019
USD ($)
ft²
Jan. 31, 2018
USD ($)
ft²
Mar. 31, 2019
USD ($)
Dec. 31, 2018
USD ($)
Nov. 30, 2018
Commitment And Contingencies [Line Items]          
Remaining lease terms     4 years 1 month 6 days    
Future minimum rent commitment     $ 9,244 $ 7,308  
Future minimum lease commitment     1,243 $ 1,313  
Cambridge, Massachusetts [Member]          
Commitment And Contingencies [Line Items]          
Lease term of contract         48 months
Future minimum lease commitment     $ 1,243    
Lab Space [Member] | Cambridge, Massachusetts [Member]          
Commitment And Contingencies [Line Items]          
Area of lease agreement | ft²   9,500      
Lease term   5 years      
Lessee, Operating Lease, Existence of Option to Extend [true false]   true      
Lease renewal term   2 years      
Future minimum rent commitment   $ 3,100      
Office Space [Member] | Cambridge, Massachusetts [Member]          
Commitment And Contingencies [Line Items]          
Area of lease agreement | ft² 5,000 16,000      
Future minimum rent commitment $ 2,600 $ 3,600      
Lease expiration period 2025-01 2022-02      
Minimum [Member]          
Commitment And Contingencies [Line Items]          
Remaining lease terms     1 year    
Maximum [Member]          
Commitment And Contingencies [Line Items]          
Remaining lease terms     6 years