Financial Derivatives - Summary of Combined Fair Values, Net of Tax of Interest Rate Derivative Instruments (Details) - USD ($) $ in Millions		Jun. 30, 2021	Sep. 30, 2020	Jun. 30, 2020
Designated as Hedging Instrument [Member] | Interest Rate Swaps [Member] | Fair Value, Inputs, Level 2 [Member]
Derivative [Line Items]
Derivative fair value, net of tax	[1]	$ (8.9)	$ (15.0)	$ (16.3)

[1] Assets are included in the consolidated balance sheets in prepaid expenses and other current assets, while liabilities are included in accrued expenses.