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Supplemental Information On Oil And Gas Exploration And Production Activities (Unaudited) (Narrative) (Details) $ in Millions | 12 Months Ended
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Dec. 31, 2015 USD ($) Mcfe $ / MMBTU $ / bbl | Dec. 31, 2014 | Dec. 31, 2014 USD ($) | Dec. 31, 2014 $ / MMBTU | Dec. 31, 2014 $ / bbl | Dec. 31, 2014 Mcfe | Dec. 31, 2013 USD ($) | Dec. 31, 2013 $ / MMBTU | Dec. 31, 2013 $ / bbl | Dec. 31, 2013 Mcfe
Reserve Quantities [Line Items] |  |  |  |  |  |  |  |  |  |
Price per unit (usd per MMbls or MMcf) | 2.59 |  |  | 4.35 | 94.99 |  |  | 3.67 | 96.78 |
Future Development Costs Estimated To Be Spent In Year One | $ | $ 170.3 |  | $ 177.6 |  |  |  | $ 158.4 |  |  |
Diamondback Energy, Inc |  |  |  |  |  |  |  |  |  |
Reserve Quantities [Line Items] |  |  |  |  |  |  |  |  |  |
Ownership interest |  | 7.20% | 7.20% | 7.20% | 7.20% | 7.20% |  |  |  |
Grizzly |  |  |  |  |  |  |  |  |  |
Reserve Quantities [Line Items] |  |  |  |  |  |  |  |  |  |
Ownership interest | 24.9999% |  |  |  |  |  |  |  |  |
Utica Shale |  |  |  |  |  |  |  |  |  |
Reserve Quantities [Line Items] |  |  |  |  |  |  |  |  |  |
Increase (decrease) in reserve during the period | 1,044,500 |  |  |  |  | 786,000 |  |  |  | 166,832
Southern Louisiana and Utica Fields |  |  |  |  |  |  |  |  |  |
Reserve Quantities [Line Items] |  |  |  |  |  |  |  |  |  |
Decrease in reserves relating to change in estimates | 444,314 |  |  |  |  | 15,837 |  |  |  |
Proved Undeveloped Reserves, Postponement of Drilling Period |  | 5 years |  |  |  |  |  |  |  |
Paloma and AEU |  |  |  |  |  |  |  |  |  |
Reserve Quantities [Line Items] |  |  |  |  |  |  |  |  |  |
Increase (decrease) in reserve during the period | 371,663 |  |  |  |  |  |  |  |  |
Rhino |  |  |  |  |  |  |  |  |  |
Reserve Quantities [Line Items] |  |  |  |  |  |  |  |  |  |
Increase (decrease) in reserve during the period |  |  |  |  |  | 12,000 |  |  |  |
Oil and condensate sales |  |  |  |  |  |  |  |  |  |
Reserve Quantities [Line Items] |  |  |  |  |  |  |  |  |  |
Price per unit (usd per MMbls or MMcf) | $ / bbl | 50.28 |  |  |  |  |  |  |  |  |
Natural Gas Liquids |  |  |  |  |  |  |  |  |  |
Reserve Quantities [Line Items] |  |  |  |  |  |  |  |  |  |
Price per unit (usd per MMbls or MMcf) | $ / bbl | 13.21 |  |  |  | 44.84 |  |  |  | 41.23 |

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