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DERIVATIVE INSTRUMENTS (Gain and Loss on Derivative Instruments) (Details) - USD ($) $ in Thousands | 3 Months Ended
--- | ---
Mar. 31, 2021 | Mar. 31, 2020
Derivative [Line Items] |  |
Net (loss) gain on natural gas, oil and NGL derivatives | $ (29,978) | $ 98,266
Natural gas derivatives |  |
Derivative [Line Items] |  |
Net (loss) gain on natural gas, oil and NGL derivatives | (25,413) | 45,853
Oil derivatives |  |
Derivative [Line Items] |  |
Net (loss) gain on natural gas, oil and NGL derivatives | (1,731) | 52,874
NGL derivatives |  |
Derivative [Line Items] |  |
Net (loss) gain on natural gas, oil and NGL derivatives | (2,834) | 920
Contingent consideration arrangement |  |
Derivative [Line Items] |  |
Net (loss) gain on natural gas, oil and NGL derivatives | $ 0 | $ (1,381)

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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=121590274&loc=SL5618551-113959 + Details
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