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Income Taxes (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended | 12 Months Ended
--- | --- | --- | ---
Mar. 31, 2018 | Mar. 31, 2017 | Mar. 31, 2018 | Mar. 31, 2017 | Sep. 30, 2018 | Sep. 30, 2017
Income Taxes |  |  |  |  |  |
Effective income tax rate (as a percent) | 70.60% | 31.00% | 9084.70% | 32.50% |  |
U.S. federal statutory rate (as a percent) |  |  |  |  |  | 35.00%
Income tax benefit related to new tax act | $ 1.4 |  | $ 501.8 |  |  |
Forecast |  |  |  |  |  |
Income Taxes |  |  |  |  |  |
U.S. federal statutory rate (as a percent) |  |  |  |  | 24.50% |

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