Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017
Gross Deferred Tax Assets
Tax loss carryforwards	$ 0.4	$ 0.5
Tax credit carryforwards	3.1	0.9
Retirement benefits and compensation accruals	9.3	10.9
Reserves and accruals	6.2	0.0
Other	4.0	1.5
Valuation allowance	(1.4)	(0.9)
Deferred Tax Assets	21.6	12.9
Gross Deferred Tax Liabilities
Intangible assets	4.1	9.1
Plant and equipment	35.2	22.9
Unremitted earnings of foreign entities	0.0	0.7
Accounting method change	0.3	0.8
Deferred tax liability, accounting method change	4.6	0.0
Other	0.4	0.2
Deferred Tax Liabilities	44.6	35.3
Net Deferred Income Tax Liability	23.0	22.4
Deferred Tax Liabilities, Deferred Expense, Reserves and Accruals	$ 0.0	$ 1.6