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Income Taxes - Narrative (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended | 12 Months Ended
--- | --- | --- | ---
Mar. 31, 2019 | Apr. 01, 2018 | Mar. 31, 2019 | Apr. 01, 2018 | Sep. 30, 2018
Income Tax Disclosure [Abstract] |  |  |  |  |
Effective tax rate (as a percent) |  |  | (0.80%) | 11.00% |
Statutory federal tax rate |  |  |  |  | 24.50%
Deferred tax benefit from tax reform remeasurement | $ 2.6 | $ 10.1 |  |  |
Deferred tax liability valuation allowance | $ 22.3 |  | $ 22.3 |  |
Effective income tax rate excluding revaluation of deferred taxes (as a percent) | 24.80% | 23.00% |  |  |
Liability for uncertain tax positions | $ 12.1 |  | $ 12.1 |  | $ 9.4
Period during which unrecognized tax benefits would affect the effective tax rate |  |  | 12 months |  |

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- Definition Tax Cuts And Jobs Act Of 2017, Incomplete Accounting, Change In Tax Rate, Provisional Income Tax Expense (Benefit) + References No definition available. + Details
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