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Business Overview - Narrative (Details) | 9 Months Ended
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Jun. 30, 2021 employee location customer market business_area | Jun. 30, 2020
Concentration Risk [Line Items] |  |
Number of market focus areas | business_area | 3 |
Number of market leveraging core competencies | market | 7 |
Number of largest customers | customer | 3 |
Revenue from Contract with Customer | Customer concentration |  |
Concentration Risk [Line Items] |  |
Percent of total revenue | 100.00% | 100.00%
Revenue from Contract with Customer | Customer concentration | Federal Government |  |
Concentration Risk [Line Items] |  |
Percent of total revenue | 99.00% |
U.S. |  |
Concentration Risk [Line Items] |  |
Number of employees | employee | 2,200 |
Number of locations in which entity operates | 30 |
Overseas |  |
Concentration Risk [Line Items] |  |
Number of locations in which entity operates | 1 |

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