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, 2024	Sep. 30, 2023
Carrying Value | Other Assets
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total assets	$ 23.1	$ 32.2
Carrying Value | Other Assets | Interest Rate Derivative Contracts
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total assets	13.3	21.3
Carrying Value | Other Liabilities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total liabilities	10.0	10.9
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	0.2
Investment Held by Rabbi Trust | Carrying Value | Other Assets
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total assets	9.8	10.9
Investment Held by Rabbi Trust | Carrying Value | Other Liabilities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total liabilities	9.8	10.9
Level 1 | Other Assets
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total assets	9.8	10.9
Level 1 | Other Assets | Interest Rate Derivative Contracts
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total assets	0.0	0.0
Level 1 | Other Liabilities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total liabilities	9.8	10.9
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
Level 1 | Investment Held by Rabbi Trust | Other Assets
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total assets	9.8	10.9
Level 1 | Investment Held by Rabbi Trust | Other Liabilities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total liabilities	9.8	10.9
Level 2 | Other Assets
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total assets	13.3	21.3
Level 2 | Other Assets | Interest Rate Derivative Contracts
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total assets	13.3	21.3
Level 2 | Other Liabilities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total liabilities	0.2	0.0
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	0.2
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 Assets | Interest Rate Derivative Contracts
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 | 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
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