PENSION AND OTHER POSTRETIREMENT BENEFITS - Postretirement Health and Life Insurance Benefits (Details) - Other Postretirement Benefits - USD ($) $ in Thousands	3 Months Ended
Jun. 30, 2018	Jun. 30, 2017
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 4	$ 3
Interest expense	83	84
Amortization of prior service cost	(177)	(178)
Actuarial loss	109	115
Net periodic pension cost (benefit)	$ 19	$ 24

Amount of gain (loss) from change in actuarial assumptions which (increases) decreases benefit obligation of defined benefit plan. Assumptions include, but are not limited to, interest, mortality, employee turnover, salary, and temporary deviation from substantive plan.

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Amount of prior service cost (credit) recognized in net periodic benefit cost (credit) of defined benefit plan.

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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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Amount of cost recognized for passage of time related to defined benefit plan.

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Amount of net periodic benefit cost (credit) for defined benefit plan.

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Amount of cost for actuarial present value of benefits attributed to service rendered by employee for defined benefit plan.

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