Fair Value Measurements and Derivatives Instruments - Summary of Effects on Consolidated Financial Statements of Designated As Cash Flow Hedges (Details) - Interest Rate Swaps - Cash Flow Hedges - Designated - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Derivative Instruments Gain Loss [Line Items]
Income (loss) recognized in Other comprehensive income (loss)	$ 0.2	$ (4.2)
Interest Expense
Derivative Instruments Gain Loss [Line Items]
Net (loss) reclassified from Accumulated other comprehensive loss into Interest expense	$ (3.0)	$ (0.8)