PROPERTY, PLANT AND EQUIPMENT (Details) - USD ($)	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Property, Plant and Equipment, Net, by Type [Abstract]
Total property, plant and equipment	$ 695,226,000	$ 571,031,000
Less: accumulated depreciation	(333,159,000)	(294,213,000)
Net property, plant and equipment	362,067,000	276,818,000	$ 111,403,000
Depreciation expense	39,929,000	37,584,000	17,255,000
Impairment of assets	2,314,000	67,372,000	0
Impairment expense	2,314,000	67,372,000	0
Wood Treatment
Property, Plant and Equipment, Net, by Type [Abstract]
Net property, plant and equipment	450,000
Impairment of assets	2,314,000	67,372,000	$ 0
Impairment expense	450,000	4,063,000
Land
Property, Plant and Equipment, Net, by Type [Abstract]
Total property, plant and equipment	36,775,000	36,276,000
Buildings
Property, Plant and Equipment, Net, by Type [Abstract]
Total property, plant and equipment	166,907,000	142,585,000
Machinery and equipment
Property, Plant and Equipment, Net, by Type [Abstract]
Total property, plant and equipment	280,432,000	257,706,000
Vehicles
Property, Plant and Equipment, Net, by Type [Abstract]
Total property, plant and equipment	18,719,000	13,497,000
Furniture and fixtures
Property, Plant and Equipment, Net, by Type [Abstract]
Total property, plant and equipment	9,865,000	9,615,000
Information systems
Property, Plant and Equipment, Net, by Type [Abstract]
Total property, plant and equipment	56,573,000	46,516,000
Finance leases
Property, Plant and Equipment, Net, by Type [Abstract]
Total property, plant and equipment	2,514,000	1,200,000
Construction in progress
Property, Plant and Equipment, Net, by Type [Abstract]
Total property, plant and equipment	$ 123,441,000	$ 63,636,000