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Asset Retirement Obligations (Tables) | 9 Months Ended
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Sep. 30, 2017
Asset Retirement Obligation Disclosure [Abstract] |
Change in asset retirement obligations | The following schedule shows the change in our asset retirement obligations for the nine months ended September 30, 2017 (dollars in thousands):
Asset retirement obligations at January 1, 2017 | $ | 624,475 |
Changes attributable to: |  |
Accretion expense | 24,170 |
Estimated cash flow revisions | 22,211 |
Asset retirement obligations at September 30, 2017 | $ | 670,856 |

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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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