Income Taxes - Schedule of Components of Income Tax Expense (Benefit) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Current:
Federal	$ 7.5	$ (28.1)	$ 12.5
State	4.7	3.8	5.0
Deferred:
Federal	(3.7)	28.4	(19.6)
State	(2.9)	0.5	(7.5)
Total income tax expense (benefit)	$ 5.6	$ 4.6	$ (9.6)