Income Taxes - Schedule of Components of Income Tax Expense (Benefit) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Current:
Federal	$ (1.3)	$ 23.1	$ 22.7
State	5.6	5.3	3.4
Deferred:
Federal	19.9	(0.8)	(22.4)
State	(1.9)	1.3	(4.2)
Valuation allowance	3.0	1.2	5.1
Total income tax (benefit) expense	$ 25.3	$ 30.1	$ 4.6