Schedule II-Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Allowance for doubtful accounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	$ 1.0	$ 0.8	$ 0.8
Change Charged to Expense	0.1	0.2	0.0
Other Changes	0.0	0.0	0.0
Balance at End of Period	1.1	1.0	0.8
Allowance for deferred tax assets
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	0.9	55.6	77.7
Change Charged to Expense	0.5	0.9	(20.8)
Other Changes	0.0	(55.6)	(1.3)
Balance at End of Period	$ 1.4	$ 0.9	$ 55.6