Fair Value Measurements and Derivative Instruments - Summary of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - Recurring - USD ($) $ in Millions	Jun. 30, 2025	Sep. 30, 2024
Carrying Value | Other Assets
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total assets	$ 7.8	$ 9.7
Carrying Value | Other Liabilities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total liabilities	9.2	12.7
Carrying Value | Other Liabilities | Interest Rate Derivative Contracts
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total liabilities	1.0	2.5
Carrying Value | Accrued Expenses and Other Current Liabilities | Fuel Derivative Contracts
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total liabilities	0.4	0.5
Investment Held by Rabbi Trust | Carrying Value | Other Assets
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total assets	7.8	9.7
Investment Held by Rabbi Trust | Carrying Value | Other Liabilities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total liabilities	7.8	9.7
Level 1 | Other Assets
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total assets	7.8	9.7
Level 1 | Other Liabilities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total liabilities	7.8	9.7
Level 1 | Other Liabilities | Interest Rate Derivative Contracts
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total liabilities	0.0	0.0
Level 1 | Accrued Expenses and Other Current Liabilities | Fuel Derivative Contracts
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total liabilities	0.0	0.0
Level 1 | Investment Held by Rabbi Trust | Other Assets
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total assets	7.8	9.7
Level 1 | Investment Held by Rabbi Trust | Other Liabilities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total liabilities	7.8	9.7
Level 2 | Other Assets
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total assets	0.0	0.0
Level 2 | Other Liabilities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total liabilities	1.4	3.0
Level 2 | Other Liabilities | Interest Rate Derivative Contracts
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total liabilities	1.0	2.5
Level 2 | Accrued Expenses and Other Current Liabilities | Fuel Derivative Contracts
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total liabilities	0.4	0.5
Level 2 | Investment Held by Rabbi Trust | Other Assets
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total assets	0.0	0.0
Level 2 | Investment Held by Rabbi Trust | Other Liabilities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total liabilities	0.0	0.0
Level 3 | Other Assets
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total assets	0.0	0.0
Level 3 | Other Liabilities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total liabilities	0.0	0.0
Level 3 | Other Liabilities | Interest Rate Derivative Contracts
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total liabilities	0.0	0.0
Level 3 | Accrued Expenses and Other Current Liabilities | Fuel Derivative Contracts
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total liabilities	0.0	0.0
Level 3 | Investment Held by Rabbi Trust | Other Assets
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total assets	0.0	0.0
Level 3 | Investment Held by Rabbi Trust | Other Liabilities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total liabilities	$ 0.0	$ 0.0