Income Taxes - Net Deferred Income Tax Liability (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016
Income Tax Disclosure [Abstract]
Other non-current assets	$ 18.1	$ 10.8
Deferred tax liabilities	37.3	42.8
Net Deferred Income Tax Liability	$ 19.2	$ 32.0