Income Taxes - Additional Disclosures (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Operating Loss Carryforwards [Line Items]
Increase (decrease) to the valuation allowance	$ (0.4)
Undistributed losses of foreign subsidiaries	63.0
Undistributed earnings of foreign subsidiaries, estimated taxes recognized upon distribution	3.5
Income tax penalties and interest expense	1.2	$ 0.2	$ (0.3)
Accrued interest and penalties	1.5	$ 0.3
State Jurisdiction
Operating Loss Carryforwards [Line Items]
Operating loss carryforward	123.0
Foreign Tax Authority
Operating Loss Carryforwards [Line Items]
Operating loss carryforward	42.0
Tax credit carryforward	$ 1.7