Derivative instruments (Details 3) - Discontinued Operations, Held-for-sale or Disposed of by Sale [Member] - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset	$ 2,537	$ 18,335	$ 260
Derivative liability fair value gross liability	3,511	0	17,449
Commodity contract [Member] \| Not designated as hedging instrument [Member] \| Disposal group current assets held for sale [Member]
Derivatives, Fair Value [Line Items]
Other derivatives not designated as hedging instruments assets at fair value	2,537	18,335	129
Commodity contract [Member] \| Not designated as hedging instrument [Member] \| Disposal group noncurrent assets held for sale [Member]
Derivatives, Fair Value [Line Items]
Other derivatives not designated as hedging instruments assets at fair value	0	0	131
Commodity contract [Member] \| Not designated as hedging instrument [Member] \| Disposal group current liabilities held for sale [Member]
Derivatives, Fair Value [Line Items]
Other derivatives not designated as hedging instruments liabilities at fair value	$ 3,511	$ 0	$ 17,449

Fair value, before effects of master netting arrangements, of a 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. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

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

-Publisher FASB

-Name Accounting Standards Codification

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-Publisher FASB

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- Definition

Fair value, before effects of master netting arrangements, of a 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. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 20

-Section 50

-Paragraph 4D

-Subparagraph (c)(2)

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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-Publisher FASB

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- Definition

Fair value as of the balance sheet date of derivative instrument not designated as hedging instrument and classified as an asset.

+ References

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-Publisher FASB

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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- Definition

Fair value of all derivative liabilities not designated as a hedging instrument.

+ References

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-Publisher FASB

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