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Derivative Financial Instruments Gains and Losses (Details) - USD ($) $ in Thousands | 3 Months Ended
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Mar. 31, 2017 | Mar. 31, 2016
Gain and loss from derivative cash settlements and changes in fair value of derivative contracts |  |
Derivative settlement (gain) loss | $ (7) | $ (147,028)
Gain (Loss) on Derivative Instruments, Net, Pretax | 114,774 | 14,228
NYMEX Oil Contracts [Member] |  |
Gain and loss from derivative cash settlements and changes in fair value of derivative contracts |  |
Derivative settlement (gain) loss | 9,084 | (99,992)
Gain (Loss) on Derivative Instruments, Net, Pretax | 49,590 | 10,432
Gas Contracts [Member] |  |
Gain and loss from derivative cash settlements and changes in fair value of derivative contracts |  |
Derivative settlement (gain) loss | (17,506) | (41,053)
Gain (Loss) on Derivative Instruments, Net, Pretax | 44,468 | 24,023
NGL Contracts [Member] |  |
Gain and loss from derivative cash settlements and changes in fair value of derivative contracts |  |
Derivative settlement (gain) loss | 8,415 | (5,983)
Gain (Loss) on Derivative Instruments, Net, Pretax | $ 20,716 | $ (20,227)

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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=64837297&loc=SL5618551-113959 + Details
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