v3.19.1

ASSET RETIREMENT OBLIGATION (Tables) | 12 Months Ended
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Dec. 31, 2018
Asset Retirement Obligation Disclosure [Abstract] |
Schedule of changes to asset retirement obligations | Following is a table of the changes to our asset retirement obligations for the following periods (in thousands):
|  | Year Ended December 31,
|  | 2018 |  | 2017 |  | 2016
Asset retirement obligation, at beginning of period |  | $ | 21,476 |  |  | $ | 19,976 |  |  | $ | 22,951 |
Liabilities settled |  | (19 | ) |  | — |  |  | (3 | )
Liabilities incurred |  | — |  |  | 29 |  |  | — |
Changes in estimated obligations |  | — |  |  | (87 | ) |  | (4,740 | )
Accretion of discount |  | 1,668 |  |  | 1,558 |  |  | 1,768 |
Total asset retirement obligation, at end of period |  | $ | 23,125 |  |  | $ | 21,476 |  |  | $ | 19,976 |

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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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