Income Taxes - Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Income Tax Disclosure [Abstract]
Current federal tax expense (benefit)	$ 74.3	$ 73.1	$ 49.1
Current state and local tax expense (benefit)	19.2	17.8	10.9
Current foreign tax expense (benefit)	(0.3)	0.7	0.9
Current income tax expense (benefit), total	93.2	91.6	60.9
Deferred federal income tax expense (benefit)	(16.7)	(7.1)	(4.9)
Deferred state and local income tax expense (benefit)	(3.7)	(1.6)	(1.1)
Deferred income taxes, total	(20.4)	(8.7)	(6.0)
Income tax expense, total	$ 72.8	$ 82.9	$ 54.9