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Inventory- Schedule of Inventory (Details) - USD ($)
$ in Thousands
Mar. 31, 2018
Dec. 31, 2017
Inventory    
Crude oil inventory $ 10,390 $ 10,427
Equipment and materials 12,649 8,940
Total inventory 23,039 19,367
Long-term inventory    
Linefill in third-party pipelines 12,506 12,200
Long-term inventory 12,506 12,200
Total $ 35,545 $ 31,567