Income Taxes - Schedule of Components of Income Tax Expense (Benefit) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Current:
Federal	$ 23.1	$ 22.7	$ 7.5
State	5.3	3.4	4.7
Deferred:
Federal	(0.8)	(22.4)	(3.7)
State	1.3	(4.2)	(2.9)
Valuation allowance	1.2	5.1	0.0
Total income tax (benefit) expense	$ 30.1	$ 4.6	$ 5.6