Income Taxes - Schedule of Components of Income Tax Expense (Benefit) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Current:
Federal	$ 22.7	$ 7.5	$ (28.1)
State	3.4	4.7	3.8
Deferred:
Federal	(22.4)	(3.7)	28.4
State	(4.2)	(2.9)	0.5
Valuation Allowance	5.1	0.0	0.0
Total income tax expense (benefit)	$ 4.6	$ 5.6	$ 4.6