EMPLOYEE BENEFIT PLANS - AMOUNTS NOT YET RECOGNIZED AS NET PERIODIC COST (Details) - OPEB - USD ($) $ in Thousands	Mar. 31, 2020	Sep. 30, 2019	Sep. 30, 2018
Regulatory Assets
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net actuarial loss	$ 69,594	$ 112,109
Prior service cost (credit)	(435)	(480)
Regulatory Assets, Total	69,159	111,629	$ 68,685
Accumulated Other Comprehensive Income (Loss)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net actuarial loss	8,958	16,367
Prior service cost (credit)	(35)	(39)
Accumulated Other Comprehensive Income (Loss), Total	$ 8,923	$ 16,328	$ 7,659

Amount, before tax, of accumulated other comprehensive (income) loss for defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

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Amount, before tax, of accumulated other comprehensive income (loss) for gain (loss) of defined benefit plan, that has not been recognized in net periodic benefit (cost) credit.

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Amount, before tax, of accumulated other comprehensive (income) loss for cost (credit) of benefit change attributable to participants' prior service from plan amendment or plan initiation of defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

+ References

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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The amount for the individual regulatory asset as itemized in a table of regulatory assets as of the end of the period.

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