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BENEFIT PLANS, Assumptions (Details) - SERP [Member]
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Weighted-average assumptions used to determine net periodic benefit cost [Abstract]      
Discount rate 4.30% 4.58% 4.09%
Rate of compensation increase [1] [1] 3.50%
Weighted-average assumptions used to determine benefit obligations [Abstract]      
Discount rate 3.68% 4.30%  
Rate of compensation increase [1]  
[1] n/a