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Derivative Financial Instruments Gains and Losses (Details) | 12 Months Ended
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Dec. 31, 2015 USD ($) | Dec. 31, 2014 USD ($) | Dec. 31, 2013 USD ($)
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net |  | $ 0 | $ 0 | $ 0
Derivative, (Gain) Loss on Derivative, Net [Abstract] |  |  |  |
Derivative Settlement Gain (Loss) |  | 512,566,000 | 12,615,000 | 22,062,000
Derivative gain |  | 408,831,000 | 583,264,000 | 3,080,000
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax | [1] | 0 | 0 | (1,115,000)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax | [2] | 0 | 0 | 1,777,000
NYMEX Oil Contracts [Member] |  |  |  |
Derivative, (Gain) Loss on Derivative, Net [Abstract] |  |  |  |
Derivative Settlement Gain (Loss) |  | 362,219,000 | 28,410,000 | (15,161,000)
Derivative gain |  | 191,165,000 | 457,082,000 | (14,665,000)
Gas Contracts [Member] |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Gain on Early Settlement of Derivatives |  | 15,300,000 | 5,600,000 |
Derivative, (Gain) Loss on Derivative, Net [Abstract] |  |  |  |
Derivative Settlement Gain (Loss) | [3] | 123,180,000 | (26,706,000) | 30,338,000
Derivative gain |  | 189,734,000 | 93,267,000 | 14,053,000
NGL Contracts [Member] |  |  |  |
Derivative, (Gain) Loss on Derivative, Net [Abstract] |  |  |  |
Derivative Settlement Gain (Loss) |  | 27,167,000 | 10,911,000 | 6,885,000
Derivative gain |  | $ 27,932,000 | $ 32,915,000 | $ 3,692,000
Cash Flow Hedging [Member] |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Derivative, Number of Instruments Held |  | 0 | 0 | 0
[1] | Reclassification from accumulated other comprehensive loss related to de-designated hedges. Refer to Note 10 - Derivative Financial Instruments for further information.
[2] | As of December 31, 2013, all commodity derivative contracts that had been previously designated as cash flow hedges had settled and had been reclassified into earnings from AOCL.
[3] | Natural gas derivative settlements for the years ended December 31, 2015, and 2014, include $15.3 million and $5.6 million, respectively, of early settlements of futures contracts as a result of divesting assets in the Company’s Mid-Continent region.

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- Definition The effective portion of gains and losses (net) on derivative instruments designated and qualifying as hedging instruments that was recognized in other comprehensive income during the current period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=56946850&loc=SL5624171-113959 + Details
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