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		9 Months Ended
	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Interest Rate Contracts
Derivative Instruments Gain Loss [Line Items]
Income (loss) recognized in Other comprehensive income (loss)	$ 3.1	$ (2.4)	$ 6.9	$ 5.6
Net income (loss) reclassified from Accumulated other comprehensive (loss) into Interest expense	0.4	1.2	1.7	4.5
Fuel Contracts [Member]
Derivative Instruments Gain Loss [Line Items]
Income (loss) recognized in Other comprehensive income (loss)	0.7	(0.3)	2.3	(0.3)
Net income (loss) reclassified from Accumulated other comprehensive (loss) into Interest expense	$ 1.4	$ 0.1	$ 1.3	$ (0.4)