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Benefit Plans, Assumptions (Details) - SERP [Member]
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Weighted-average assumptions used to determine net periodic benefit cost [Abstract]      
Discount rate 3.68% 4.30% 4.58%
Rate of compensation increase [1]
Weighted-average assumptions used to determine benefit obligations [Abstract]      
Discount rate 4.36% 3.68%  
Rate of compensation increase [1]  
[1] n/a