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, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Interest Rate Swaps
Derivative Instruments Gain Loss [Line Items]
Income (loss) recognized in Other comprehensive income	$ 1.8	$ (0.2)	$ 5.4	$ (0.3)
Interest Rate Swaps | Interest Expense
Derivative Instruments Gain Loss [Line Items]
Net (loss) income reclassified from Accumulated other comprehensive Income (loss) into Interest expense/Cost of services provided	(0.1)	(0.8)	(1.7)	(6.1)
Fuel Swap Contracts
Derivative Instruments Gain Loss [Line Items]
Income (loss) recognized in Other comprehensive income	0.0	1.2	0.2	3.2
Fuel Swap Contracts | Cost of Services Provided
Derivative Instruments Gain Loss [Line Items]
Net (loss) income reclassified from Accumulated other comprehensive Income (loss) into Interest expense/Cost of services provided	$ 0.0	$ 1.2	$ 1.5	$ 0.8