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Asset Retirement Obligations (Tables) | 12 Months Ended
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Dec. 31, 2019
Asset Retirement Obligation Disclosure [Abstract] |
Change in asset retirement obligations | The following table shows the change in our asset retirement obligations for 2019 and 2018 (dollars in thousands):
| 2019 |  | 2018
Asset retirement obligations at the beginning of year | $ | 726,545 |  |  | $ | 679,529 |
Changes attributable to: |  |  |  |  |
Accretion expense | 39,726 |  |  | 36,876 |
Settlements | (12,591 | ) |  | (9,726 | )
Estimated cash flow revisions | (96,462 | ) |  | 2,002 |
Newly incurred or acquired obligations | — |  |  | 17,864 |
Asset retirement obligations at the end of year | $ | 657,218 |  |  | $ | 726,545 |

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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://fasb.org/us-gaap/role/ref/legacyRef -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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