Fair Value Measurements and Derivative 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	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2019	Sep. 30, 2018
Derivative Instruments Gain Loss [Line Items]
(Loss) income recognized in Other comprehensive income (loss)	$ (3.4)	$ (10.2)	$ 9.8
Interest Expense
Derivative Instruments Gain Loss [Line Items]
Net loss reclassified from Accumulated other comprehensive loss into Interest expense	$ (7.4)	$ (8.1)	$ (9.8)