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Asset Retirement Obligation (Tables) | 12 Months Ended
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Dec. 31, 2012
Information Related to Asset Retirement Obligation | The following table reflects information related to our asset retirement obligations:
Balance at December 31, 2010 |  | $ | 173,673 |
Additions to asset retirement obligations |  |  | 708 |
Accretion expense |  |  | 10,573 |
Liabilities settled |  |  | (4,292 | )
Balance at December 31, 2011 |  |  | 180,662 |
Additions to asset retirement obligations |  |  | 5,434 |
Accretion expense |  |  | 10,871 |
Liabilities settled |  |  | (7,308 | )
Balance at December 31, 2012 |  | $ | 189,659 |

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- Definition Tabular disclosure of the changes in carrying amount of a liability for asset retirement obligations, for changes such as new obligations, changes in estimates of existing obligations, spending on existing obligations, property dispositions, and foreign currency translation. + References Reference 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 + Details
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