Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Income Tax Disclosure [Abstract]
Income tax expense	$ 1.1	$ 2.3	$ 3.3	$ 2.1	$ 2.4	$ 6.8	$ 5.5	$ 3.3	$ 8.8	$ 18.0	$ 22.4
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax									0.0	0.0	(0.4)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized (Gain) Loss Arising During Period, Tax									1.0	0.2	(0.8)
Adjustments to Additional Paid in Capital, Income Tax Benefit from Share-based Compensation									(0.1)	(0.8)	(0.5)
Other Comprehensive Income (Loss), Tax									9.9	17.4	20.7
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense									0.0
Operating Loss Carryforwards	30.1				15.7				30.1	15.7
Deferred Tax Assets, Operating Loss Carryforwards, Domestic	21.9				12.4				21.9	12.4
Deferred Tax Assets, Net of Valuation Allowance, Operating Loss Carryforwards, State and Local	4.4								4.4
Deferred Tax Assets, Tax Credit Carryforwards, Alternative Minimum Tax	1.3								1.3
Deferred Tax Assets, Valuation Allowance	4.0				3.6				4.0	3.6
Valuation Allowance, Deferred Tax Asset, Change in Amount									0.4
Income (Loss) from Continuing Operations before Income Taxes, Domestic									(24.7)	(9.7)	$ 16.5
Deferred Tax Liabilities, Gross	4.9								4.9
Deferred Tax Liabilities, Unrealized Gains on Trading Securities	3.1								3.1
Undistributed Earnings of Foreign Subsidiaries	$ 321.3				$ 294.3				$ 321.3	$ 294.3