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Significant Accounting Policies - Accounts and Receivable and Allowance for Doubtful Accounts (Details) - Allowance for doubtful accounts
$ in Thousands
9 Months Ended
Sep. 30, 2021
USD ($)
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]  
Balance at Beginning of Period $ 9,502
Charged to Costs and Expenses 7,221
Write-offs (593)
Balance at End of Period $ 16,130