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EMPLOYEE BENEFIT PLANS - Weighted average assumptions used to determine the projected benefit obligation and net benefit cost (Details) - Retirement Income Plan
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
PROJECTED BENEFIT OBLIGATION:        
Discount rate 3.70% 4.65% 4.05%  
Rate of compensation increase  
NET BENEFIT COST:        
Discount rate 4.65% 4.05% 4.50%  
Expected return on plan assets 7.00% 7.00% 7.00% 7.00%
Rate of compensation increase