|**Asset Retirement Obligations (Tables)**             | 3 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 beginning of period, January 1, 2015$73,855Obligations incurred with development activities302Accretion expense1,560Obligations discharged with asset retirements(777)Balance end of period, March 31, 201574,940Less current portion(2,792)Long-term portion$72,148
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|                                                      | Amount                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|                                                      | (in thousands)                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|Balance at beginning of period, January 1, 2015       | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
|Obligations incurred with development activities      | 302                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Accretion expense                                     | 1,560                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Obligations discharged with asset retirements         | (777                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|Balance end of period, March 31, 2015                 | 74,940                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Less current portion                                  | (2,792                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Long-term portion                                     | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
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