Income Taxes - Deferred Tax Assets and Liabilites (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016
Tax Credit Carryforward [Line Items]
Deferred Tax Assets, Tax Credit Carryforwards, Research	$ 0.4
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Share-based Compensation Cost	3.7	$ 4.3
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Pensions	0.1	1.9
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Employee Compensation	2.0	2.0
Deferred Tax Assets, Operating Loss Carryforwards, Foreign	5.6	2.0
Deferred Tax Assets, Operating Loss Carryforwards, State and Local	6.6	4.9
Deferred Tax Assets, Operating Loss Carryforwards, Domestic	21.9	12.4
Deferred Tax Assets, Intangible Assets	6.1	8.3
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Allowance for Doubtful Accounts	1.4	1.6
Deferred Tax Assets, Tax Credit Carryforwards, Alternative Minimum Tax	1.6	1.4
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits	3.6	3.3
Deferred Tax Assets, Other	1.9	1.8
Deferred Tax Assets, Gross	54.5	43.9
Deferred Tax Assets, Valuation Allowance	(4.0)	(3.6)
Deferred Tax Assets, Net of Valuation Allowance	50.5	40.3
Deferred Tax Liabilities, Unrealized Gains on Trading Securities	3.2	1.3
Deferred Tax Liabilities, Prepaid Expenses	2.5	1.9
Deferred Tax Liabilities, Property, Plant and Equipment	2.2	2.6
Deferred Tax Liabilities, Gross	7.9	5.8
Deferred tax assets, Net	$ 42.6	$ 34.5