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Derivative Financial Instruments Gains and Losses (Details) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended
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Jun. 30, 2017 | Jun. 30, 2016 | Jun. 30, 2017 | Jun. 30, 2016
Gain and loss from derivative cash settlements and changes in fair value of derivative contracts |  |  |  |
Document Fiscal Year Focus |  |  | 2017 |
Derivative settlement (gain) loss | $ (16,303) | $ (101,710) | $ (16,310) | $ (248,738)
Net derivative (gain) loss | (55,189) | 163,351 | (169,963) | 149,123
Oil Contracts [Member] |  |  |  |
Gain and loss from derivative cash settlements and changes in fair value of derivative contracts |  |  |  |
Derivative settlement (gain) loss | 2,754 | (72,164) | 11,838 | (172,156)
Net derivative (gain) loss | (38,194) | 60,773 | (87,784) | 50,341
Gas Contracts [Member] |  |  |  |
Gain and loss from derivative cash settlements and changes in fair value of derivative contracts |  |  |  |
Derivative settlement (gain) loss | (21,751) | (31,439) | (39,257) | (72,492)
Net derivative (gain) loss | (6,038) | 62,489 | (50,506) | 38,466
NGL Contracts [Member] |  |  |  |
Gain and loss from derivative cash settlements and changes in fair value of derivative contracts |  |  |  |
Derivative settlement (gain) loss | 2,694 | 1,893 | 11,109 | (4,090)
Net derivative (gain) loss | $ (10,957) | $ 40,089 | $ (31,673) | $ 60,316

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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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