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, 2022	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021
Interest Rate Swaps
Derivative Instruments Gain Loss [Line Items]
Income recognized in Other comprehensive income (loss)	$ 2.6	$ 0.2	$ 3.7	$ 0.0
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	(0.7)	(0.7)	(1.6)	(5.2)
Fuel Swap Contracts
Derivative Instruments Gain Loss [Line Items]
Income recognized in Other comprehensive income (loss)	0.0	1.9	0.2	1.8
Fuel Swap Contracts | Cost of Services Provided
Derivative Instruments Gain Loss [Line Items]
Income recognized in Other comprehensive income (loss)		$ 0.4		$ (0.4)
Net (loss) income reclassified from Accumulated other comprehensive Income (loss) into Interest expense/Cost of services provided	$ 0.0		$ 1.5