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Asset retirement obligations (“ARO”) (Tables) | 3 Months Ended
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Mar. 31, 2012
Asset Retirement Obligation Disclosure [Abstract] |
Schedule of Change in Asset Retirement Obligations | The reconciliation of the changes in the asset retirement obligations is presented below:
| Three months ended March 31, 2012 | Year ended December 31, 2011
Beginning balance, ARO liability | $ | 15,171 |  | $ | 14,274 |
Additional ARO liability incurred | 291 |  | 1,110 |
ARO liabilities settled | (345 | ) | (1,315 | )
Accretion expense | 292 |  | 1,102 |
Ending balance, ARO liability | $ | 15,409 |  | $ | 15,171 |

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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 -Topic 410 -SubTopic 30 -Publisher FASB -Number -Article -Subparagraph -Name Accounting Standards Codification -Paragraph 5 -Section 50 -URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13201-110859 + Details
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