Income Taxes - Additional Disclosures (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Operating Loss Carryforwards [Line Items]
Income tax expense (benefit) allocated to discontinued operations	$ 0.2	$ 0.1	$ (15.1)
Increase to the valuation allowance	2.4
Undistributed losses of foreign subsidiaries	50.0
Undistributed earnings of foreign subsidiaries, estimated taxes recognized upon distribution	2.5
Decrease in unrecognized tax benefits reasonably possible in next 12 months	1.8
State Jurisdiction
Operating Loss Carryforwards [Line Items]
Operating loss carryforward	121.0
Foreign Tax Authority
Operating Loss Carryforwards [Line Items]
Operating loss carryforward	40.3
Tax credit carryforward	$ 2.6