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DERIVATIVE INSTRUMENTS (Net (Loss) Gain on Derivative Instruments) (Details) - USD ($) $ in Thousands | 3 Months Ended
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Mar. 31, 2019 | Mar. 31, 2018
Derivative [Line Items] |  |
Net loss on natural gas, oil, and NGL derivatives | $ (20,045) | $ (16,529)
Natural gas derivatives |  |
Derivative [Line Items] |  |
Net loss on natural gas, oil, and NGL derivatives | (16,431) | (9,696)
Oil derivatives |  |
Derivative [Line Items] |  |
Net loss on natural gas, oil, and NGL derivatives | (454) | (9,147)
Natural gas liquids derivatives |  |
Derivative [Line Items] |  |
Net loss on natural gas, oil, and NGL derivatives | $ (3,160) | $ 2,314

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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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