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DERIVATIVE INSTRUMENTS (Net (Loss) Gain on Derivative Instruments) (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
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Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2018 | Sep. 30, 2017
Derivative [Line Items] |  |  |  |
Net (loss) gain on natural gas, oil, and NGL derivatives | $ (9,663) | $ (22,860) | $ (96,737) | $ 141,588
Natural gas derivatives |  |  |  |
Derivative [Line Items] |  |  |  |
Net (loss) gain on natural gas, oil, and NGL derivatives | 14,101 | (7,077) | (26,789) | 135,868
Oil derivatives |  |  |  |
Derivative [Line Items] |  |  |  |
Net (loss) gain on natural gas, oil, and NGL derivatives | (11,610) | (6,571) | (45,176) | 12,477
Natural gas liquids derivatives |  |  |  |
Derivative [Line Items] |  |  |  |
Net (loss) gain on natural gas, oil, and NGL derivatives | $ (12,154) | $ (9,212) | $ (24,772) | $ (6,757)

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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://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5618551-113959 + Details
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