PROPERTY, PLANT AND EQUIPMENT - Summary of Property Plant and Equipment (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Sep. 30, 2020
Property, Plant and Equipment [Line Items]
Property plant and equipment gross	$ 834,220	$ 815,517
Accumulated depreciation and amortization	(493,215)	(471,553)
Total	341,005	343,964
Land, building and building improvements
Property, Plant and Equipment [Line Items]
Property plant and equipment gross	169,081	167,005
Machinery and equipment
Property, Plant and Equipment [Line Items]
Property plant and equipment gross	611,187	595,126
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property plant and equipment gross	$ 53,952	$ 53,386