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Accounts Receivable - Concentration of Credit Risk (Details) - Credit Concentration Risk - Accounts receivable, net
9 Months Ended 12 Months Ended
Sep. 30, 2021
Dec. 31, 2020
29 days or less past due    
Concentration Risk [Line Items]    
Concentration risk, percentage 99.00% 97.00%
59 days or less past due    
Concentration Risk [Line Items]    
Concentration risk, percentage 99.00% 98.00%