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

Fair value, after offset of derivative liability, of financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, before offset against an obligation to return collateral under a master netting arrangement. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

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Fair value, after offset of derivative asset, of financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, elected not to be and before offset against a right to receive collateral under a master netting arrangement. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

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