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Leases - Additional Information (Details)
$ in Thousands
 1 Months Ended 12 Months Ended
Sep. 30, 2020
ft²
Dec. 31, 2017
ft²
Nov. 30, 2015
Dec. 31, 2020
USD ($)
Dec. 31, 2019
USD ($)
Jan. 31, 2018
ft²
Operating Leased Assets [Line Items]            
Operating lease option to terminate     true true    
Letter of credit       $ 878    
Letter of credit expiry date       Sep. 30, 2028    
Operating lease, payments       $ 4,878 $ 2,602  
Weighted-average remaining lease term       8 years 3 months 18 days 9 years 3 months 18 days  
Weighted-average discount rate       10.40% 10.40%  
215 First Street [Member]            
Operating Leased Assets [Line Items]            
Operating lease agreement expiration date     2020-12      
399 Binney Street [Member]            
Operating Leased Assets [Line Items]            
Operating lease agreement expiration date 2029-04 2029-04        
Land subject to ground leases | ft² 1,824 44,336       44,807