Income Taxes - Unrecognized Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Income Tax Disclosure [Abstract]
Unrecognized tax benefits, beginning balance	$ 1.5	$ 1.5	$ 0.0
Unrecognized tax benefits, increase resulting from current period tax positions	0.0	0.0	1.5
Unrecognized tax benefits, ending balance	$ 1.5	$ 1.5	$ 1.5