Subject to master netting agreements (Details 4) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014
Commodity derivative instruments assets [Member]
Derivative instruments [Line Items]
Derivative asset, fair value, gross asset	$ 8,633	$ 18,335	$ 11,581
Gross amount not offset	0	0	(44)
Derivative asset, fair value, net	8,633	18,335	11,537
Total assets [Member]
Derivative instruments [Line Items]
Derivative asset, fair value, gross asset	8,633	18,335	11,581
Gross amount not offset	0	0	(44)
Derivative asset, fair value, net	$ 8,633	$ 18,335	11,537
Commodity derivatives - liabilities [Member]
Derivative instruments [Line Items]
Derivative liability fair value gross liability			44
Gross amount not offset			(44)
Derivative liability, fair value, net			0
Total liabilities [Member]
Derivative instruments [Line Items]
Derivative liability fair value gross liability			44
Gross amount not offset			(44)
Derivative liability, fair value, net			$ 0

Fair value, after effects of master netting arrangements, deduction of assets not subject to a master netting arrangement and elected not to be offset, 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, offset against an obligation to return collateral.

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Fair value 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, elected not to be offset, deducted from derivative assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

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+ References

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