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Asset Retirement Obligations (Table) | 12 Months Ended
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Dec. 31, 2011
Asset Retirement Obligation [Abstract] |
Asset retirement obligations |
(Dollars in thousands) |  | 2011 |  | 2010
Balance, beginning of period |  | $ | 128,709 |  |  | $ | 118,742 |
| Additional liabilities accrued |  |  | 2,105 |  |  |  | 4,757 |
| Revisions in estimated cash outflows |  |  | 5,888 |  |  |  | (1,382 | )
| Disposition of assets |  |  | (1,323 | ) |  |  | (2,086 | )
| Accretion expense |  |  | 8,023 |  |  |  | 8,678 |
Balance, end of period |  | $ | 143,402 |  |  | $ | 128,709 |

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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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