v3.8.0.1

Derivative Instruments and Fair Value Measurements - Summary of Cash Settlements and Change in Fair Value of Commodity Derivatives (Detail) - Derivatives Not Designated as Hedging Instruments [Member] - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Derivatives Fair Value [Line Items] |  |  |
Commodity derivative (loss) gain | $ (262) | $ (5,484) | $ 19,275
Net Cash (Payment) Receipt on derivatives Settlements [Member] |  |  |
Derivatives Fair Value [Line Items] |  |  |
Commodity derivative (loss) gain | (4,359) | 6,132 | 52,489
Non-Cash Fair Value Gain (Loss) on Derivatives [Member] |  |  |
Derivatives Fair Value [Line Items] |  |  |
Commodity derivative (loss) gain | $ 4,097 | $ (11,616) | $ (33,214)

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- Definition Aggregate net gain (loss) on all derivative instruments recognized in earnings during the period, before tax effects. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5618551-113959 + Details
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