Long-Term Debt (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Debt Instrument
Debt, long-term and short-term, combined amount, total	$ 1,090.0	$ 840.0
Unamortized debt issuance expense	(5.7)	(6.9)
Long-term debt	1,084.3	833.1
Long-Term Debt, Maturity, Year Five	1,090.0
Estimated future interest payments on debt	342.7
Estimated future interest payments on debt, next 12 months	74.8
Letter of Credit
Debt Instrument
Maximum borrowing capacity on line of credit	20.0
Revolving Credit Facility
Debt Instrument
Debt, long-term and short-term, combined amount, total	250.0	0.0
Maximum borrowing capacity on line of credit	500.0	250.0
Payments of Financing Costs	2.1			$ 1.5
Proceeds from borrowing under line of credit	700.0	0.0	$ 115.0
Repayments of lines of credit	(450.0)	(25.0)	$ (189.0)
Remaining borrowing capacity on line of credit	247.6	250.0
Letters of credit outstanding, amount	2.4
7.00% Senior Notes Maturing in March 2030
Debt Instrument
Debt, long-term and short-term, combined amount, total	$ 840.0	$ 840.0
Senior Notes [Member] | 7.00% Senior Notes Maturing in March 2030
Debt Instrument
Long-term Debt, Gross				840.0
Payments of debt issuance costs and deferred financing fees				$ (10.2)