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RETIREMENT PLANS: (Details 10)
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Retirement Benefits [Abstract]      
Discount rate (percent)   4.22% 3.60%
Initial weighted health care cost trend rate (percent)   .05 .05
Ultimate health care cost trend rate (percent) 500.00% 500.00%  
Year that the rate is assumed to stabilize and remain unchanged (percent) 2019 2018