BENEFIT PLANS (Components of Net Periodic Benefit Cost- Pension Benefits) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Weighted-average assumptions used to determine net periodic benefit cost for years ended December 31
Expected return on plan assets	7.00%
Pension Benefits [Member]
Components of Net Periodic Benefit Cost
Service cost	$ 6,715	$ 5,343	$ 4,851
Interest cost	36,230	36,505	44,065
Expected return on plan assets	(48,506)	(51,562)	(54,736)
Settlement charge	0	0	2,031
Amortization of prior service cost (credit)	1,340	(43)	48
Amortization of actuarial loss	7,397	6,163	21,641
Net periodic benefit cost (credit)	3,176	(3,594)	17,900
Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income
Net actuarial loss (gain)	7,879	33,682	(3,615)
Prior service cost	10,868	0	0
Reclassification of actuarial gain (loss)	(7,397)	(6,163)	(23,672)
Reclassification of prior service (cost) credit	(1,340)	43	(48)
Amount recognized in other comprehensive income	10,010	27,562	(27,335)
Amount recognized in net periodic pension benefit cost and other comprehensive income	$ 13,186	$ 23,968	$ (9,435)
Weighted-average assumptions used to determine net periodic benefit cost for years ended December 31
Discount rate — PBO	4.29%	4.55%	4.14%
Discount rate — service cost	4.63%	4.68%	4.14%
Discount rate — interest cost	3.63%	3.79%	4.14%
Expected return on plan assets	7.00%	7.50%	7.50%
Weighted-average assumptions used to determine benefit obligation at December 31
Discount rate	3.72%	4.29%	4.54%