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Major Clients (Details) - Revenue - Customer Concentration Risk | 12 Months Ended
--- | ---
Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2019
Percentage of total revenue |  |  |
Period for which criteria of threshold percentage for disclosure not met in past | 5 years |  |
Maximum |  |  |
Percentage of total revenue |  |  |
Percentage of revenue accounted for by no other single client (as a percent) | 10.00% |  |
Agencies of U.S. Federal Government |  |  |
Percentage of total revenue |  |  |
Concentration (as a percent) | 8.00% | 8.00% | 9.00%

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- Definition Represents the period for which criteria of threshold percentage for disclosure not met in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
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