EMPLOYEE BENEFIT PLANS - AMOUNTS NOT YET RECOGNIZED AS NET PERIODIC COST (Details) - USD ($) $ in Thousands	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Pension | Regulatory Assets
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net actuarial loss (gain)	$ 7,810	$ 22,172
Prior service cost (credit)	0	0
Regulatory Assets, Total	7,810	22,172	$ 24,638
Pension | Accumulated Other Comprehensive Income (Loss)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net actuarial loss (gain)	(1,955)	1,557
Prior service cost (credit)	0	0
Accumulated Other Comprehensive Income (Loss), Total	(1,955)	1,557	742
OPEB | Regulatory Assets
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net actuarial loss (gain)	76,120	54,056
Prior service cost (credit)	(43,245)	(53,046)
Regulatory Assets, Total	32,875	1,010	30,046
OPEB | Accumulated Other Comprehensive Income (Loss)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net actuarial loss (gain)	26,443	18,414
Prior service cost (credit)	(13,542)	(16,821)
Accumulated Other Comprehensive Income (Loss), Total	$ 12,901	$ 1,593	$ 5,498