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, 2020	Dec. 31, 2019
Interest Rate Swaps
Derivative Instruments Gain Loss [Line Items]
(Loss) income recognized in Other comprehensive income (loss)	$ (0.2)	$ 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	(4.2)	(3.0)
Fuel Swap Contracts
Derivative Instruments Gain Loss [Line Items]
(Loss) income recognized in Other comprehensive income (loss)	0.2	0.1
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	$ (0.8)	$ 0.4