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Leases - Additional Information (Detail)
$ in Thousands
 3 Months Ended
Mar. 13, 2019
USD ($)
ft²
m²
Aug. 31, 2017
USD ($)
ft²
Mar. 31, 2019
USD ($)
Jan. 01, 2019
USD ($)
Lessee, Lease, Description [Line Items]        
Right-of-use assets     $ 2,705  
Operating lease liabilities     4,116  
Lease liability, net of current portion     3,275  
Current portion of lease liability     841  
Accounting Standards Update 2016-02 [Member]        
Lessee, Lease, Description [Line Items]        
Right-of-use assets     2,026 $ 2,026
Operating lease liabilities     $ 2,538 2,538
Lease liability, net of current portion       1,925
Current portion of lease liability       613
Net deferred, accrued and prepaid rent       $ 512
Cambridge Lease Agreement [Member]        
Lessee, Lease, Description [Line Items]        
Lease expiration date   Jul. 31, 2022    
Current office space under lease agreement | ft²   13,000    
Option to extend the lease agreement     The Company has the option to extend the lease for one period of five additional years.  
Lease, renewal term of contract   5 years    
Base rent   $ 810    
Waltham Lease [Member]        
Lessee, Lease, Description [Line Items]        
Current office space under lease agreement | ft² 6,000      
Base rent $ 459      
Agreement commencement date Jan. 01, 2019      
Operating lease expiration 5 years      
Vienna Lease [Member]        
Lessee, Lease, Description [Line Items]        
Current office space under lease agreement | m² 400      
Base rent $ 155      
Agreement commencement date Mar. 01, 2019      
Lease, term of contract 2 years      
Period for written notice for cancellable 3 months