|**Asset Retirement Obligations**                                         | 6 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
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|**Asset Retirement Obligation Disclosure [Abstract]**                    |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Asset Retirement Obligation Disclosure                                   | ASSET RETIREMENT OBLIGATIONSThe following table presents the changes in carrying amounts of the asset retirement obligations associated with our working interest in crude oil and natural gas properties:Amount(in thousands)Balance at December 31, 2012$62,563Obligations incurred with development activities211Accretion expense2,481Revisions in estimated cash flows963Obligations discharged with disposal of properties and asset retirements(7,481)Balance at June 30, 201358,737Liabilities held for sale (1)(22,370)Less current portion(1,000)Long-term portion$35,367______________(1)Represents asset retirement obligations related to our assets held for sale. See Note 12, Assets Held for Sale, Divestitures and Discontinued Operations, for additional information regarding the planned sale of these properties.
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|                                                                         | Amount                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|                                                                         | (in thousands)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
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|Balance at December 31, 2012                                             | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       
|Obligations incurred with development activities                         | 211                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Accretion expense                                                        | 2,481                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|Revisions in estimated cash flows                                        | 963                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Obligations discharged with disposal of properties and asset retirements | (7,481                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|Balance at June 30, 2013                                                 | 58,737                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|Liabilities held for sale (1)                                            | (22,370                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 
|Less current portion                                                     | (1,000                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|Long-term portion                                                        | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       
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|(1)                                                                      | Represents asset retirement obligations related to our assets held for sale. See Note 12, Assets Held for Sale, Divestitures and Discontinued Operations, for additional information regarding the planned sale of these properties.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    

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