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Asset Retirement Obligations (Tables) | 12 Months Ended
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Dec. 31, 2017
Asset Retirement Obligations [Abstract] |
Schedule of Reconciliation of Beginning and Ending Aggregate Carrying Amount of Asset Retirement Obligations |
﻿ |  |  |  |
﻿ |  |  |  |
﻿(Thousands of dollars) | 2017 |  | 2016
﻿Balance at beginning of year | $ | 781,057 |  | 825,312
﻿ Accretion expense |  | 42,590 |  | 46,742
﻿ Liabilities incurred |  | 52,331 |  | 13,690
﻿ Revisions of previous estimates |  | (47,612) |  | (4,511)
﻿ Liabilities settled |  | (29,111) |  | (20,589)
﻿ Liabilities assumed by purchaser of oil and gas assets |  | (87,456) |  | (91,883)
﻿ Changes due to translation of foreign currencies |  | 10,340 |  | 12,296
﻿ Balance at end of year |  | 722,139 |  | 781,057
﻿ Liabilities reported as held for sale at end of year 1 |  | – |  | (85,900)
﻿ Current portion of liability at end of year 2 |  | (12,840) |  | (13,629)
﻿ Noncurrent portion of liability at end of year | $ | 709,299 |  | 681,528
﻿ 1 Liabilities held for sale related to Seal properties in Canada which were sold in January 2017. 2 Included in Other accrued liabilities on the Consolidated Balance Sheet. ﻿

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- Definition Tabular disclosure of the carrying amount of a liability for asset retirement obligations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 + Details
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