Quarterly report pursuant to Section 13 or 15(d)

Property and equipment - Summary (Details)

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Property and equipment - Summary (Details) - USD ($)
$ in Thousands
Sep. 30, 2018
Dec. 31, 2017
Property, Plant and Equipment [Line Items]    
Total property and equipment $ 630,386 $ 431,332
Less: accumulated DD&A (218,198) (114,375)
Total other property and equipment 2,472 1,283
Total property and equipment, net 632,858 432,615
Proved oil and natural gas properties    
Property, Plant and Equipment [Line Items]    
Total property and equipment 722,284 423,611
Unproved oil and natural gas properties    
Property, Plant and Equipment [Line Items]    
Total property and equipment 124,742 121,690
Land    
Property, Plant and Equipment [Line Items]    
Total property and equipment 1,558 406
Other property and equipment    
Property, Plant and Equipment [Line Items]    
Total property and equipment 5,759 4,345
Less: accumulated DD&A $ (3,287) $ (3,062)