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Derivative Instruments (Narrative) (Details) | 12 Months Ended
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Dec. 31, 2015 USD ($) MMBTU / d $ / MMBTU | Dec. 31, 2014 USD ($) financial_institution | Dec. 31, 2013 USD ($)
Derivative [Line Items] |  |  |
Reduction to oil and condensate sales |  |  | $ 9,800,000
Number of financial institutions | financial_institution |  | 4 |
Gain on fair value hedge ineffectiveness, net | $ (83,671,000) | $ (121,148,000) | 18,189,000
Gain on fair value hedge ineffectiveness |  |  | 9,100,000
Loss related to amortization of OCI from hedging activity |  |  | $ 9,100,000
Production delivered under fixed price swaps, percentage | 46.00% |  |
January 2017 - December 2017 |  |  |
Derivative [Line Items] |  |  |
Daily Volume (MMBtu/day) | MMBTU / d | 30,000 |  |
Weighted Average Price | $ / MMBTU | 3.33 |  |
January 2017 - December 2017 | Short |  |  |
Derivative [Line Items] |  |  |
Daily Volume (MMBtu/day) | MMBTU / d | 30,000 |  |
Weighted Average Price | $ / MMBTU | 3.33 |  |
Swap |  |  |
Derivative [Line Items] |  |  |
AOCI before Tax, Attributable to Parent | $ 0 |  |
Swaption |  |  |
Derivative [Line Items] |  |  |
AOCI before Tax, Attributable to Parent | 0 |  |
Basis Swap |  |  |
Derivative [Line Items] |  |  |
AOCI before Tax, Attributable to Parent | $ 0 |  |

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