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Operating Segments, Geographic Analysis and Major Customers (Concentration) (Details) - Total operating revenues - Operating revenues
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Shell      
Concentration Risk      
Percentage of concentration 26.00% 26.00% 17.00%
Equinor      
Concentration Risk      
Percentage of concentration 21.00% 18.00%  
Chevron      
Concentration Risk      
Percentage of concentration 17.00% 21.00% 29.00%
Petrobras      
Concentration Risk      
Percentage of concentration     14.00%