BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Long-Lived Asset and Finite-Lived Intangible Asset Impairments (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Sep. 30, 2025	Mar. 28, 2025	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Finite-Lived Intangible Assets [Line Items]
Asset impairment charges			$ 214,386	$ 0	$ 0
HDPE Business
Finite-Lived Intangible Assets [Line Items]
Asset impairment charges	$ 66,717	$ 127,733	$ 194,450
Minimum | Customer relationships
Finite-Lived Intangible Assets [Line Items]
Weighted Average Useful Life (Years)	6 years		6 years
Minimum | Other
Finite-Lived Intangible Assets [Line Items]
Weighted Average Useful Life (Years)	1 year		1 year
Maximum | Customer relationships
Finite-Lived Intangible Assets [Line Items]
Weighted Average Useful Life (Years)	14 years		14 years
Maximum | Other
Finite-Lived Intangible Assets [Line Items]
Weighted Average Useful Life (Years)	20 years		20 years