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Summary of Significant Accounting Policies (Tables) | 12 Months Ended
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Dec. 31, 2017
Accounting Policies [Abstract] |
Net Changes in Capitalized Exploratory Well Costs | Net changes in capitalized exploratory well costs are reflected in the following table for the periods presented:
| December 31,
| 2017 |  | 2016 |  | 2015
| (In thousands)
Beginning of period | $ | 2,097 |  |  | $ | 2,097 |  |  | $ | 34,522 |
Exploratory well cost additions (pending determination of proved reserves) | 10 |  |  | — |  |  | 51,803 |
Exploratory well cost reclassifications (successful determination of proved reserves) | (571 | ) |  | — |  |  | (84,228 | )
Exploratory well dry hole costs (unsuccessful in adding proved reserves) | (1,536 | ) |  | — |  |  | — |
End of period | $ | — |  |  | $ | 2,097 |  |  | $ | 2,097 |

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- Definition Tabular disclosure of the change in capitalized exploratory costs during the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 1B -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=68064819&loc=SL6806780-109447 + Details
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