|**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 December 31, 2016$92,387Obligations incurred with development activities2,415Accretion expense3,434Obligations discharged with asset retirements(7,431)Balance at June 30, 201790,805Less current portion(12,938)Long-term portion$77,867
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|                                                      | Amount                                                                                                                                                                                                                                                                                                                                                                                                                                                 
|                                                      | (in thousands)                                                                                                                                                                                                                                                                                                                                                                                                                                         
|                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                        
|Balance at December 31, 2016                          | $                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|Obligations incurred with development activities      | 2,415                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|Accretion expense                                     | 3,434                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|Obligations discharged with asset retirements         | (7,431                                                                                                                                                                                                                                                                                                                                                                                                                                                 
|Balance at June 30, 2017                              | 90,805                                                                                                                                                                                                                                                                                                                                                                                                                                                 
|Less current portion                                  | (12,938                                                                                                                                                                                                                                                                                                                                                                                                                                                
|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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