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
	Dec. 31, 2021	Dec. 31, 2020
Interest Rate Swaps
Derivative Instruments Gain Loss [Line Items]
Income recognized in Other comprehensive income (loss)	$ 1.1	$ (0.2)
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	(0.8)	(4.2)
Fuel Swap Contracts
Derivative Instruments Gain Loss [Line Items]
Income recognized in Other comprehensive income (loss)	0.2	0.2
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	$ 1.5	$ (0.8)