Derivative Financial Instruments - Fair Value of Derivative Instruments in the Consolidated Balance Sheet (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020
Derivatives designated as hedging instruments | Interest rate swap contract | Other long-term assets
Derivative Asset [Abstract]
Derivative Assets	$ 12,335	$ 0
Derivative Liability [Abstract]
Derivative Liabilities	0	0
Derivatives designated as hedging instruments | Interest rate swap contract | Accrued expenses and other current liabilities
Derivative Asset [Abstract]
Derivative Assets	0	0
Derivative Liability [Abstract]
Derivative Liabilities	2,995	11,992
Derivatives designated as hedging instruments | Interest rate swap contract | Other long-term liabilities
Derivative Asset [Abstract]
Derivative Assets	0	0
Derivative Liability [Abstract]
Derivative Liabilities	0	26,000
Derivatives not designated as hedging instruments | Foreign exchange contracts | Accrued expenses and other current liabilities
Derivative Asset [Abstract]
Derivative Assets	0	0
Derivative Liability [Abstract]
Derivative Liabilities	388	165
Derivatives not designated as hedging instruments | Foreign exchange contracts | Prepaid expenses and other current assets
Derivative Asset [Abstract]
Derivative Assets	0	27
Derivative Liability [Abstract]
Derivative Liabilities	$ 0	$ 0