LONG-LIVED ASSET IMPAIRMENT -WOOD TREATMENT - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Impaired Long-Lived Assets Held and Used [Line Items]
Goodwill	$ 718,647	$ 710,071	$ 101,083
Recognized tax benefit	(30,519)	(23,891)	$ (51,668)
Intangible assets	623,794	706,874
Wood Treatment
Impaired Long-Lived Assets Held and Used [Line Items]
Total long-lived assets	2,314	67,372
Goodwill	35,000
Recognized tax benefit	608	$ 17,072
Intangible assets	$ 3,800