EMPLOYEE BENEFIT PLANS, AMOUNTS NOT YET RECOGNIZED AS NET PERIODIC COST (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Sep. 30, 2014
Regulatory Assets [Member] | Pension [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net actuarial loss	$ 86,070	$ 60,797
Prior service cost (credit)	890	997
Net transition obligation	0	0
Regulatory Assets, Total	86,960	61,794
Regulatory Assets [Member] | OPEB [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net actuarial loss	52,462	45,809
Prior service cost (credit)	(1,725)	(2,035)
Net transition obligation	0	0
Regulatory Assets, Total	50,737	43,774
Accumulated Other Comprehensive Income (Loss) [Member] | Pension [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net actuarial loss	25,632	17,570
Prior service cost (credit)	8	11
Net transition obligation	0	0
Accumulated Other Comprehensive Income (Loss), Total	25,640	17,581
Accumulated Other Comprehensive Income (Loss) [Member] | OPEB [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net actuarial loss	1,495	425
Prior service cost (credit)	(253)	(308)
Net transition obligation	0	0
Accumulated Other Comprehensive Income (Loss), Total	$ 1,242	$ 117