| **Properties and Equipment**             | 3 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
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| **Oil and Gas Property [Abstract]**      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
| Property, Plant and Equipment Disclosure | PROPERTIES AND EQUIPMENTThe following table presents the components of properties and equipment, net of accumulated depreciation, depletion and amortization ("DD&A"): March 31, 2015 December 31, 2014 (in thousands)Properties and equipment, net:   Crude oil and natural gas properties   Proved$2,360,880 $2,267,165Unproved188,518 188,206Total crude oil and natural gas properties2,549,398 2,455,371Equipment and other31,217 29,562Land and buildings9,016 9,015Construction in progress178,804 137,937Properties and equipment, at cost2,768,435 2,631,885Accumulated DD&A(887,432) (831,699)Properties and equipment, net$1,881,003 $1,800,186    The following table presents impairment charges recorded for crude oil and natural gas properties: Three Months Ended March 31, 2015 2014 (in thousands)Continuing operations:   Amortization of individually insignificant unproved properties$2,484 $910Discontinued operations:   Amortization of individually insignificant unproved properties— 69Total impairment of crude oil and natural gas properties$2,484 $979     |

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| - Definition
The entire disclosure for long-lived, physical assets used in the normal conduct of business and not intended for resale. Includes, but is not limited to, accounting policies and methodology, roll forwards, depreciation, depletion and amortization expense, including composite depreciation, accumulated depreciation, depletion and amortization expense, useful lives and method used, income statement disclosures, assets held for sale and public utility disclosures.
+ References
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