PROPERTY, PLANT AND EQUIPMENT - Summary of Property Plant and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Sep. 30, 2020
Property, Plant and Equipment [Line Items]
Property plant and equipment gross	$ 825,668	$ 815,517
Accumulated depreciation and amortization	(482,962)	(471,553)
Total	342,706	343,964
Land, building and building improvements
Property, Plant and Equipment [Line Items]
Property plant and equipment gross	168,557	167,005
Machinery and equipment
Property, Plant and Equipment [Line Items]
Property plant and equipment gross	603,270	595,126
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property plant and equipment gross	$ 53,841	$ 53,386