Quarterly report pursuant to Section 13 or 15(d)

Accounts Receivable, Net (Details)

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Accounts Receivable, Net (Details) - USD ($)
$ in Thousands
Dec. 31, 2021
Sep. 30, 2021
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Allowance for credit losses $ (7,742) $ (8,044)
Accounts receivable, net 849,410 834,819
Billed and billable receivables    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Accounts Receivable Gross 717,804 718,728
Unbilled receivables    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Accounts Receivable Gross $ 139,348 $ 124,135