Fair Value Measurements and Derivatives 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, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Interest Rate Swaps
Derivative Instruments Gain Loss [Line Items]
(Loss) income recognized in Other comprehensive income (loss)	$ (8.1)	$ (1.9)	$ (7.9)	$ (6.1)
Interest Rate Swaps | Interest Expense
Derivative Instruments Gain Loss [Line Items]
Net (loss) income reclassified from Accumulated other comprehensive loss into Interest expense	(3.8)	(2.6)	(6.8)	(3.4)
Fuel Swap Contracts
Derivative Instruments Gain Loss [Line Items]
(Loss) income recognized in Other comprehensive income (loss)	(5.5)	$ 0.9	(5.5)	$ 0.9
Fuel Swap Contracts | Interest Expense
Derivative Instruments Gain Loss [Line Items]
Net (loss) income reclassified from Accumulated other comprehensive loss into Interest expense	$ (0.1)		$ 0.2