|**Asset Retirement Obligations (Tables)**                                    | 9 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
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|**Asset Retirement Obligation Disclosure [Abstract]**                        |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Schedule of Change in Asset Retirement Obligation                            | The 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 activities337Accretion expense3,667Revisions in estimated cash flows251Obligations discharged with divestitures of properties and asset retirements(7,376)Balance at September 30, 201359,442Less: Liabilities held for sale (1)22,788Less: Current portion1,000Long-term portion$35,654______________(1)Represents asset retirement obligations related to our assets held for sale. See Note 12, Assets Held for Sale, Divestitures and Discontinued Operations and Note 15, Subsequent Events, for additional information regarding the potential 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                             | 337                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|Accretion expense                                                            | 3,667                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Revisions in estimated cash flows                                            | 251                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|Obligations discharged with divestitures of properties and asset retirements | (7,376                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|Balance at September 30, 2013                                                | 59,442                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|Less: Liabilities held for sale (1)                                          | 22,788                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|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 and Note 15, Subsequent Events, for additional information regarding the potential sale of these properties.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    

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