EMPLOYEE BENEFIT PLANS - AMOUNTS NOT YET RECOGNIZED AS NET PERIODIC COST (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Regulatory Assets | Pension
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net actuarial loss (gain)	$ 35,157	$ 55,922
Prior service cost (credit)	164	265
Regulatory Assets, Total	35,321	56,187	$ 103,564
Regulatory Assets | OPEB
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net actuarial loss (gain)	20,110	60,468
Prior service cost (credit)	0	(133)
Regulatory Assets, Total	20,110	60,335	83,301
Accumulated Other Comprehensive Income (Loss) | Pension
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net actuarial loss (gain)	5,003	22,790
Prior service cost (credit)	0	0
Accumulated Other Comprehensive Income (Loss), Total	5,003	22,790	33,004
Accumulated Other Comprehensive Income (Loss) | OPEB
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net actuarial loss (gain)	(6,822)	12,707
Prior service cost (credit)	0	(11)
Accumulated Other Comprehensive Income (Loss), Total	$ (6,822)	$ 12,696	$ 13,823