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 | 
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available. 
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- Definition Amount, before allowance for credit loss, of right to consideration from customer for product sold and service rendered in normal course of business, classified as current. Reference 1: http://www.xbrl.org/2003/role/disclosureRef 
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- Definition Amount, after allowance for credit loss, of right to consideration from customer for product sold and service rendered in normal course of business, classified as current. Reference 1: http://www.xbrl.org/2003/role/disclosureRef 
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- Definition Amount of allowance for credit loss on accounts receivable, classified as current. Reference 1: http://www.xbrl.org/2003/role/disclosureRef 
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