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Summary of Significant Accounting Policies - Net Changes in Capitalized Exploratory Well Costs (Detail) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Increase (Decrease) in Capitalized Exploratory Well Costs that are Pending Determination of Proved Reserves [Roll Forward] |  |  |
Beginning of period | $ 2,097 | $ 2,097 | $ 34,522
Exploratory well cost additions (pending determination of proved reserves) | 10 | 0 | 51,803
Exploratory well cost reclassifications (successful determination of proved reserves) | (571) | 0 | (84,228)
Exploratory well dry hole costs (unsuccessful in adding proved reserves) | (1,536) | 0 | 0
End of period | $ 0 | $ 2,097 | $ 2,097

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- Definition Additions to capitalized exploratory well costs that were added during the reporting period pending the determination of proved reserves. + 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)(1) -URI http://asc.fasb.org/extlink&oid=68064819&loc=SL6806780-109447 + Details
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- Definition The amount of capitalized exploratory well costs that is pending the determination of proved reserves. This does not include amounts that were capitalized and subsequently expensed in the same annual 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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- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. + References No definition available. + Details
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- Definition Previously capitalized costs of the drilling of wells that were reclassified as part of the costs of the enterprise's wells and related equipment and facilities at the time that proved reserves were found. + 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)(2) -URI http://asc.fasb.org/extlink&oid=68064819&loc=SL6806780-109447 + Details
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- Definition Dry hole costs from oil and gas producing activities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 360 -Section 25 -Paragraph 9 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=96866604&loc=d3e64954-109465 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 23 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62136-109447 + Details
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