Annual report pursuant to Section 13 and 15(d)

Supplemental Information On Oil And Gas Exploration And Production Activities (Unaudited) (Costs Incurred In Oil and Gas Property Acquisition and Development Activities) (Details)

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Supplemental Information On Oil And Gas Exploration And Production Activities (Unaudited) (Costs Incurred In Oil and Gas Property Acquisition and Development Activities) (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Costs Incurred, Oil and Gas Property Acquisition, Exploration, and Development Activities [Line Items]      
Acquisition $ 810,755 $ 440,288 $ 338,153
Development of proved undeveloped properties 642,811 864,511 408,121
Exploratory 0 2,249 26,174
Recompletions 13,894 45,658 44,633
Capitalized asset retirement obligation 8,800 2,095 3,556
Total 1,476,260 1,354,801 820,637
Diamondback Energy, Inc      
Costs Incurred, Oil and Gas Property Acquisition, Exploration, and Development Activities [Line Items]      
Acquisition 0 0 44,534
Development of proved undeveloped properties 0 0 6,369
Exploratory 0 0 17,491
Capitalized asset retirement obligation 0 0 50
Total 0 0 68,444
Investment in Grizzly Oil Sands ULC      
Costs Incurred, Oil and Gas Property Acquisition, Exploration, and Development Activities [Line Items]      
Acquisition 396 1,230 0
Development of proved undeveloped properties $ 47 7,107 0
Exploratory 0 0
Capitalized asset retirement obligation $ 282 1,055 0
Total $ 725 $ 9,392 $ 0