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Derivative instruments (Details 3) - Discontinued operations, held-for-sale or disposed of by sale [Member] - USD ($) $ in Thousands | Sep. 30, 2015 | Dec. 31, 2014 | Sep. 30, 2014
--- | --- | --- | ---
Derivatives, Fair Value [Line Items] |  |  |
Derivative asset, fair value, gross asset | $ 8,633 | $ 18,335 | $ 11,581
Derivative liability fair value gross liability | 0 | 0 | 44
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 | 8,633 | 18,335 | 11,322
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 | 259
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 | $ 0 | $ 0 | $ 44

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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) -URI http://asc.fasb.org/extlink&oid=51814546&loc=SL51823488-111719 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4B -Subparagraph (a),(c) -URI http://asc.fasb.org/extlink&oid=56946850&loc=SL5624163-113959 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 55 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=51825145&loc=SL20226000-175313 + Details
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