| **Assets Held for Sale, Divestitures and Discontinued Operations (Tables)** | 3 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
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| **Discontinued Operations and Disposal Groups [Abstract]**                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
| Schedule of Discontinued Operations                                         | ontinued operations for the Piceance Basin and NECO divestitures:Condensed consolidated statements of operations - discontinued operations Three Months Ended March 31, 2013   Revenues  Crude oil, natural gas and NGLs sales $10,274Sales from natural gas marketing 450Well operations, pipeline income and other 450Total revenues 11,174   Costs, expenses and other  Production costs 5,393Cost of natural gas marketing 454Depreciation, depletion and amortization 2,258Other 495Total costs, expenses and other 8,600   Income from discontinued operations 2,574Provision for income taxes (1,037)Income from discontinued operations, net of tax $1,537    |

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| - Definition
Tabular disclosure of disposal groups, which may include the gain (loss) recognized in the income statement and the income statement caption that includes that gain (loss), amounts of revenues and pretax profit or loss reported in discontinued operations, the classification and carrying value of the assets and liabilities comprising the disposal group, and the segment in which the disposal group was reported. Also may include the amount of adjustments to amounts previously reported in discontinued operations such as resolution of contingencies arising from the disposal transaction or the operations of the component prior to disposal.
+ References
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