BENEFIT PLANS (Components of Net Periodic Benefit Cost- Other Postretirement Benefits) (Details) - Postretirement Benefits [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Components of Net Periodic Benefit Cost
Service cost	$ 1,167	$ 1,123	$ 1,894
Interest cost	1,260	1,209	2,485
Amortization of prior service cost (credit)	(4,236)	(4,236)	(4,232)
Amortization of actuarial (gain) loss	(1,587)	(1,751)	37
Net periodic benefit cost (credit)	(3,396)	(3,655)	184
Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income
Net actuarial loss (gain)	342	(111)	(35,209)
Reclassification of actuarial gain (loss)	1,587	1,751	(37)
Reclassification of prior service (cost) credit	4,236	4,236	4,232
Amount recognized in other comprehensive income	6,165	5,876	(31,014)
Amount recognized in net periodic pension benefit cost and other comprehensive income	$ 2,769	$ 2,221	$ (30,830)
Weighted-average assumptions used to determine net periodic benefit cost for years ended December 31
Discount rate — PBO	3.59%	3.69%	3.50%
Discount rate — service cost	3.96%	3.77%	3.50%
Discount rate — interest cost	2.89%	2.81%	3.50%
Weighted-average assumptions used to determine benefit obligation at December 31
Discount rate	3.33%	3.58%	3.69%