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Asset Retirement Obligations (Table) | 12 Months Ended
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Dec. 31, 2012
Asset Retirement Obligation [Abstract] |
Asset retirement obligations |
(Dollars in thousands) | 2012 |  | 2011
Balance, beginning of period | $ | 143,402 |  | $ | 128,709
| Additional liabilities accrued |  | 5,578 |  |  | 2,105
| Revisions in estimated cash outflows (1) |  | 22,588 |  |  | 5,888
| Disposition of assets |  | (2,674) |  |  | (1,323)
| Accretion expense (2) |  | 10,713 |  |  | 8,023
Balance, end of period | $ | 179,607 |  | $ | 143,402
(1) | In 2012, included $14.9 million as a result of changes in expected settlement dates related to the Divestiture Transaction.
(2) | In 2012, included $0.2 million of incremental accretion related to the Divestiture Transaction.

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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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