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Subject to master netting agreements (Details 4) (USD $) In Thousands, unless otherwise specified | Sep. 30, 2014 | Dec. 31, 2013 | Sep. 30, 2013
--- | --- | --- | ---
Derivative instruments [Line Items] |  |  |
Derivative asset, fair value, gross asset | $ 11,581 | $ 1,950 | $ 6,144
Derivative liability fair value gross liability | 44 | 7,483 | 9,889
Commodity derivatives [Member] |  |  |
Derivative instruments [Line Items] |  |  |
Derivative asset, fair value, gross asset | 11,581 | 1,950 | 6,144
Gross amount not offset | (44) | (1,950) | (4,939)
Derivative asset, fair value, net | 11,537 | 0 | 1,205
Total assets [Member] |  |  |
Derivative instruments [Line Items] |  |  |
Derivative asset, fair value, gross asset | 11,581 | 1,950 | 6,144
Gross amount not offset | (44) | (1,950) | (4,939)
Derivative asset, fair value, net | 11,537 | 0 | 1,205
Commodity derivatives - liabilities [Member] |  |  |
Derivative instruments [Line Items] |  |  |
Derivative liability fair value gross liability | 44 | 7,483 | 9,889
Gross amount not offset | (44) | (1,950) | (4,939)
Derivative liability, fair value, net | 0 | 5,533 | 4,950
Total liabilities [Member] |  |  |
Derivative instruments [Line Items] |  |  |
Derivative liability fair value gross liability | 44 | 7,483 | 9,889
Gross amount not offset | (44) | (1,950) | (4,939)
Derivative liability, fair value, net | $ 0 | $ 5,533 | $ 4,950

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