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Income Taxes - Narrative (Details) | 12 Months Ended | 24 Months Ended | 33 Months Ended
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Sep. 30, 2020 | Sep. 30, 2019 | Sep. 30, 2018 | Sep. 30, 2020 | Sep. 30, 2020
Income Tax Disclosure [Abstract] |  |  |  |  |
Statutory income tax rate | 21.00% | 21.00% | 24.53% | 21.00% | 21.00%
Returns open to examination, minimum (years) | 3 years |  |  |  |
Returns open to examination, maximum (years) | 5 years |  |  |  |
Returns open to examination, state impact of federal changes, maximum (years) | 2 years |  |  |  |

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