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Income Taxes (Details) - USD ($) $ in Millions | 3 Months Ended
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Dec. 31, 2016 | Dec. 31, 2015
Income Taxes |  |
Effective tax rate (as a percent) | 27.40% | 62.90%
Federal statutory rate (as a percent) | 35.00% |
Favorable tax impact driven by changes in geographical mix | $ 4.1 |
Gross Book Tax Differences of Foreign Subsidiaries | 1,600.0 |
Undistributed earnings related to foreign subsidiaries | $ 113.2 |

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