|**Asset Retirement Obligations (Tables)**                                | 6 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 interests in crude oil and natural gas properties:Amount(in thousands)Balance at beginning of period, January 1, 2016$89,492Obligations incurred with development activities843Accretion expense3,623Obligations discharged with disposal of properties and asset retirements(5,475)Balance end of period, June 30, 201688,483Less current portion(6,900)Long-term portion$81,583
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|                                                                         | Amount                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
|                                                                         | (in thousands)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
|                                                                         |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|Balance at beginning of period, January 1, 2016                          | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|Obligations incurred with development activities                         | 843                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Accretion expense                                                        | 3,623                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Obligations discharged with disposal of properties and asset retirements | (5,475                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
|Balance end of period, June 30, 2016                                     | 88,483                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
|Less current portion                                                     | (6,900                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
|Long-term portion                                                        | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
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+ ReferencesReference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 30 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13201-110859
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