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Asset Retirement Obligations (Tables) | 12 Months Ended
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Dec. 31, 2012
Asset Retirement Obligation Disclosure [Abstract] |
Reconciliation of Beginning and Ending Aggregate Carrying Amounts of Asset Retirement Obligation | The following table presents the balance and activity of the asset retirement obligations for the years ended December 31 (in thousands).
| 2012 |  | 2011 |  | 2010
Asset retirement obligations at January 1 | $ | 128,116 |  |  | $ | 119,877 |  |  | $ | 111,137 |
Liability incurred upon acquiring and drilling wells | 7,479 |  |  | 5,716 |  |  | 17,347 |
Liability assumed in acquisition | 371,365 |  |  | — |  |  | — |
Revisions in estimated cash flows | 34,654 |  |  | 7,574 |  |  | (17,017 | )
Liability settled or disposed in current period | (72,200 | ) |  | (14,419 | ) |  | (1,011 | )
Accretion | 28,996 |  |  | 9,368 |  |  | 9,421 |
Asset retirement obligations at December 31 | 498,410 |  |  | 128,116 |  |  | 119,877 |
Less: current portion | 118,504 |  |  | 32,906 |  |  | 25,360 |
Asset retirement obligations, net of current | $ | 379,906 |  |  | $ | 95,210 |  |  | $ | 94,517 |

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- Definition Tabular disclosure of the carrying amount of a liability for asset retirement obligations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 + Details
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