EMPLOYEE BENEFIT PLANS - AMOUNTS EXPECTED TO BE RECOGNIZED IN NET PERIODIC BENEFIT COST (Details) $ in Thousands	12 Months Ended
	Sep. 30, 2018 USD ($)
Pension
Regulatory Assets
Net actuarial loss	$ 4,662
Prior service cost (credit)	102
Total	4,764
Accumulated Other Comprehensive Income (Loss)
Net actuarial loss	1,103
Prior service cost (credit)	0
Total	1,103
OPEB
Regulatory Assets
Net actuarial loss	5,527
Prior service cost (credit)	(312)
Total	5,215
Accumulated Other Comprehensive Income (Loss)
Net actuarial loss	643
Prior service cost (credit)	(53)
Total	$ 590