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Commitments (Tables) | 12 Months Ended
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Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract] |
Summary of Future Minimum Lease Payments for Non-Cancelable Operating Leases | The Company has several non-cancelable operating leases, primarily for rental of office space, that have a term of more than one year. The future minimum lease payments for the operating leases at December 31, 2017 are as follows.
(Thousands of dollars) |  | Operating Leases |
2018 |  | $ | 486 |
2019 |  |  | 172 |
Total minimum payments |  | $ | 658 |
Reconciliation of Liability for Plugging and Abandonment Costs | A reconciliation of the liability for plugging and abandonment costs for the years ended December 31, 2017 and 2016 is as follows:
|  | Year Ended December 31, |
(Thousands of dollars) |  | 2017 |  |  | 2016 |
Asset retirement obligation at beginning of period |  | $ | 17,505 |  |  | $ | 11,737 |
Liabilities incurred |  |  | 45 |  |  |  | 68 |
Liabilities settled |  |  | (676 | ) |  |  | (288 | )
Accretion expense |  |  | 768 |  |  |  | 498 |
Revisions in estimated liabilities |  |  | 5,936 |  |  |  | 5,490 |
Asset retirement obligation at end of period |  | $ | 23,578 |  |  | $ | 17,505 |

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- Definition Tabular disclosure for lessee's operating leases. Includes, but is not limited to, description of lessee's operating lease, existence and terms of renewal or purchase options and escalation clauses, restrictions imposed by lease, such as those concerning dividends, additional debt, and further leasing, rent holidays, rent concessions, or leasehold improvement incentives and unusual provisions or conditions. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 20 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=77902758&loc=d3e41502-112717 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 10 -Section 55 -Paragraph 40 -Subparagraph (Note 1,3) -URI http://asc.fasb.org/extlink&oid=82846649&loc=d3e38371-112697 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=84164451&loc=d3e36991-112694 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=77902758&loc=d3e41499-112717 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 460 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=82913245&loc=d3e12069-110248 + Details
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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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