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Commitments and Contingencies - Additional Information (Detail)
 3 Months Ended
Feb. 12, 2019
USD ($)
ft²
Oct. 01, 2015
Mar. 31, 2020
USD ($)
Mar. 31, 2019
USD ($)
Other Commitments [Line Items]        
Total lease payments over the initial term     $ 10,837,000  
Lease expense     303,000 $ 140,000
Operating cash flows from operating leases     300,000 100,000
Additional right-of-use-assets     0 0
Research and Development [Member]        
Other Commitments [Line Items]        
Lease expense     0 100,000
General and Administrative [Member]        
Other Commitments [Line Items]        
Lease expense     $ 300,000  
General and Administrative [Member] | Maximum [Member]        
Other Commitments [Line Items]        
Lease expense       $ 100,000
Boston [Member] | Massachusetts [Member] | Shigo Center Plaza Owners LLC [Member]        
Other Commitments [Line Items]        
Area of office space | ft² 17,705      
Operating lease term 124 months      
Lease extension period 60 months      
Letter of credit $ 1,300,000      
Operating lease, existence of option to extend true      
Lease rent payment start date Jun. 21, 2019      
Total lease payments over the initial term $ 10,700,000      
Sandiego [Member] | California [Member]        
Other Commitments [Line Items]        
Lease expiration date   Dec. 31, 2024