Fair Value Measurements and Derivative Instruments - Summary of Effects on Consolidated Financial Statements of Designated As Cash Flow Hedges (Details) - Cash Flow Hedges - Designated - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Mar. 31, 2025	Mar. 31, 2024
Interest Rate Contracts
Derivative Instruments Gain Loss [Line Items]
(Loss) Income recognized in Other comprehensive (loss) income	$ (2.4)	$ 3.6	$ 5.6	$ 0.0
Net income (loss) reclassified from Accumulated other comprehensive income (loss) into Interest expense	1.2	2.8	4.5	8.4
Fuel Contracts
Derivative Instruments Gain Loss [Line Items]
(Loss) Income recognized in Other comprehensive (loss) income	(0.3)	(0.2)	(0.3)	(0.1)
Net income (loss) reclassified from Accumulated other comprehensive income (loss) into Interest expense	$ 0.1	$ 0.1	$ (0.4)	$ 0.1