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Income Taxes - Narrative (Details) - USD ($) $ in Thousands | 12 Months Ended
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Sep. 30, 2019 | Sep. 30, 2018 | Sep. 30, 2017
Income Tax Disclosure [Abstract] |  |  |
Statutory income tax rate | 21.00% | 24.53% | 35.00%
Liability for uncertain tax positions | $ 0 | $ 2,679 |
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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