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Leases - Narrative (Details)
$ in Thousands
 1 Months Ended 3 Months Ended
Jul. 31, 2019
USD ($)
ft²
Mar. 31, 2021
USD ($)
Mar. 31, 2020
USD ($)
Dec. 31, 2020
USD ($)
Operating Leased Assets [Line Items]        
Lessee-paid construction costs   $ 735 $ 673  
Operating lease, weighted average discount rate, percent   8.90% 8.90%  
65 Grove Street, Watertown,MA        
Operating Leased Assets [Line Items]        
Area of additional office space leased | ft² 25,078      
Lessee-paid construction costs $ 800      
Term of contract 8 years      
Letter of credit        
Operating Leased Assets [Line Items]        
Long-term restricted cash   $ 1,400   $ 1,400