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Derivative Instruments - Realized and Unrealized Gains and Losses from Commodity Derivative Instruments (Detail) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Derivative Instruments and Hedging Activities Disclosure [Abstract] |  |  |
Net gain (loss) on derivative instruments | $ 28,457 | $ (71,657) | $ (105,317)

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- Definition Amount of increase (decrease) in the fair value of derivatives recognized in the income statement. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4A -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5618551-113959 + Details
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- References No definition available. + Details
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