Fair Value Measurements and Derivative Instruments - Summary of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - Recurring - USD ($) $ in Millions	Mar. 31, 2025	Sep. 30, 2024
Carrying Value | Other Assets
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total assets	$ 10.1	$ 9.7
Carrying Value | Other Assets | Interest Rate Derivative Contracts
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total assets	2.5
Carrying Value | Other Liabilities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total liabilities	(7.6)	(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		(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		(0.5)
Investment Held by Rabbi Trust | Carrying Value | Other Assets
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total assets	7.6	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	(7.6)	(9.7)
Level 1 | Other Assets
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total assets	7.6	9.7
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
Level 1 | Other Liabilities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total liabilities	(7.6)	(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
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	7.6	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	(7.6)	(9.7)
Level 2 | Other Assets
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total assets	2.5	0.0
Level 2 | Other Assets | Interest Rate Derivative Contracts
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total assets	2.5
Level 2 | Other Liabilities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total liabilities	0.0	(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		(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		(0.5)
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 Assets | Interest Rate Derivative Contracts
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total assets	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
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