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Asset Retirement Obligations (Tables) | 12 Months Ended
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Dec. 31, 2017
Asset Retirement Obligations [Abstract] |
Summary of Changes In Asset Retirement Obligations |
﻿ |  |  |  |  |  |  |  |  |
﻿(in thousands) |  |  | 2017 |  |  | 2016 |  |  | 2015
﻿Balance at January 1 |  | $ | 18,612 |  | $ | 16,166 |  | $ | 14,846
﻿Accretion |  |  | 951 |  |  | 903 |  |  | 778
﻿Additions |  |  | — |  |  | — |  |  | 1,085
﻿Acquisitions and dispositions |  |  | (103) |  |  | 1,544 |  |  | —
﻿Revisions |  |  | 703 |  |  | (1) |  |  | (543)
﻿Balance at December 31 |  | $ | 20,163 |  | $ | 18,612 |  | $ | 16,166
﻿

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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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