EMPLOYEE BENEFIT PLANS - ASSUMED HCCTR (Details) - OPEB - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
HCCTR	7.40%	6.60%	6.90%
Ultimate HCCTR	4.50%	4.50%	4.50%
Effect of a 1 percentage point increase in the HCCTR on:
Year-end benefit obligation	$ 30,818	$ 26,710	$ 43,217
Total service and interest cost	2,117	2,544	2,959
Effect of a 1 percentage point decrease in the HCCTR on:
Year-end benefit obligation	(25,283)	(21,853)	(34,669)
Total service and interest costs	$ (1,700)	$ (1,966)	$ (2,253)