EMPLOYEE BENEFIT PLANS - AMOUNTS NOT YET RECOGNIZED AS NET PERIODIC COST (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Pension | Regulatory Assets
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net actuarial loss	$ 22,172	$ 24,577
Prior service cost (credit)	0	61
Regulatory Assets, Total	22,172	24,638	$ 35,321
Pension | Accumulated Other Comprehensive Income (Loss)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net actuarial loss	1,557	742
Prior service cost (credit)	0	0
Accumulated Other Comprehensive Income (Loss), Total	1,557	742	5,003
OPEB | Regulatory Assets
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net actuarial loss	54,056	30,046
Prior service cost (credit)	(53,046)	0
Regulatory Assets, Total	1,010	30,046	20,110
OPEB | Accumulated Other Comprehensive Income (Loss)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net actuarial loss	18,414	5,498
Prior service cost (credit)	(16,821)	0
Accumulated Other Comprehensive Income (Loss), Total	$ 1,593	$ 5,498	$ (6,822)