Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended	12 Months Ended
	Mar. 31, 2017	Mar. 31, 2017	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Effective tax rate (as a percent)	109.00%			123.00%
U.S. statutory tax rate (as a percent)		35.00%
Unrecognized tax benefits, exclusive of interest and penalties	$ 11.1	$ 11.1		$ 10.2
Unrecognized tax benefits from permanent tax adjustments that, if recognized, would affect the effective rate	8.3	8.3
Estimated unrecognized tax benefits resulting from possible resolution of reviews by domestic and international taxing authorities	6.3	6.3
Deferred tax liability from repatriate of earnings	26.7	26.7
Additional income tax expense (benefit)					$ 35.8
Deferred tax asset valuation allowance	$ 9.0	$ 9.0
Forecast
Repatriated earnings			$ 105.0