PROPERTY, PLANT AND EQUIPMENT - Summary of Property Plant and Equipment (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Sep. 30, 2020
Property, Plant and Equipment [Line Items]
Property plant and equipment gross	$ 840,875	$ 815,517
Accumulated depreciation and amortization	(502,113)	(471,553)
Total	338,762	343,964
Land, building and building improvements
Property, Plant and Equipment [Line Items]
Property plant and equipment gross	169,588	167,005
Machinery and equipment
Property, Plant and Equipment [Line Items]
Property plant and equipment gross	615,780	595,126
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property plant and equipment gross	$ 55,507	$ 53,386