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Summary of Significant Accounting Policies - Summary of Concentration Risk (Details) - Customer Concentration Risk
3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2021
Sep. 30, 2020
Sep. 30, 2021
Sep. 30, 2020
Dec. 31, 2020
Service revenue percentage | Customer A          
Concentration Risk [Line Items]          
Concentration risk 27.00% 33.00% 27.00% 33.00%  
Service revenue percentage | Customer B          
Concentration Risk [Line Items]          
Concentration risk 11.00% 11.00% 11.00% 13.00%  
Accounts receivable percentage | Customer A          
Concentration Risk [Line Items]          
Concentration risk     26.00%   22.00%
Accounts receivable percentage | Customer B          
Concentration Risk [Line Items]          
Concentration risk     13.00%   16.00%