Derivative Financial Instruments - Fair Value of Derivative Instruments in the Consolidated Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Sep. 30, 2020
Derivatives designated as hedging instruments | Interest rate swap contract | Accrued expenses, income taxes payable and other current liabilities
Derivatives, Fair Value [Line Items]
Derivative Assets	$ 0	$ 0
Derivative Liabilities	2,869	11,992
Derivatives designated as hedging instruments | Interest rate swap contract | Other long-term liabilities
Derivatives, Fair Value [Line Items]
Derivative Assets	0	0
Derivative Liabilities	3,813	26,000
Derivatives not designated as hedging instruments | Foreign exchange contracts | Accrued expenses, income taxes payable and other current liabilities
Derivatives, Fair Value [Line Items]
Derivative Assets	0	0
Derivative Liabilities	52	165
Derivatives not designated as hedging instruments | Foreign exchange contracts | Prepaid expenses and other current assets
Derivatives, Fair Value [Line Items]
Derivative Assets	289	27
Derivative Liabilities	$ 0	$ 0