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Leases - Additional Information (Details)
$ in Millions
12 Months Ended
Dec. 31, 2020
USD ($)
ft²
Dec. 31, 2019
USD ($)
Dec. 31, 2018
USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]      
Operating lease cost $ 2.3 $ 2.3  
Short-term lease cost 0.4 0.4  
Non-lease component expense 1.5 1.4  
Rent expense     $ 3.6
Operating lease, payments $ 2.6 $ 2.5  
Washington, D.C. Lease      
New Accounting Pronouncements or Change in Accounting Principle [Line Items]      
Leased square footage | ft² 33,534    
Renewal term of lease agreement 5 years    
London Lease      
New Accounting Pronouncements or Change in Accounting Principle [Line Items]      
Leased square footage | ft² 2,880    
Renewal term of lease agreement 3 years    
Sublease | Washington, D.C. Lease      
New Accounting Pronouncements or Change in Accounting Principle [Line Items]      
Leased square footage | ft² 9,928