Income Taxes - Rate (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Income Tax Disclosure [Abstract]
Effective income tax rate reconciliation at federal statutory income tax rate, amount	$ 60.7	$ 69.2	$ 46.3
State income taxes, net of effect on federal tax	12.6	13.5	8.4
Non-deductible compensation	5.6	3.2	1.9
Other, net (none in excess of 5% of computed tax)	(6.1)	(3.0)	(1.7)
Income tax expense, total	$ 72.8	$ 82.9	$ 54.9