PENSION AND OTHER POSTRETIREMENT BENEFITS - Postretirement Health and Life Insurance Benefits (Details) - Other Postretirement Benefits - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 4	$ 3	$ 7	$ 7
Interest expense	83	85	166	169
Amortization of prior service cost	(177)	(178)	(355)	(355)
Actuarial loss	109	115	219	230
Net periodic pension cost (benefit)	$ 19	$ 25	$ 37	$ 51