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Gains and losses on derivative instruments (Details 2) - USD ($) $ in Thousands | 3 Months Ended
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Mar. 31, 2016 | Mar. 31, 2015
Derivative instruments [Line Items] |  |
Amount of (gain) loss reclassified from accumulated other comprehensive loss (effective portion), net of tax | $ 92 | $ 99
Designated as hedging instrument [Member] | Interest rate derivatives designated as cash flow hedges [Member] |  |
Derivative instruments [Line Items] |  |
Amount of (gain) loss reclassified from accumulated other comprehensive loss (effective portion), net of tax | 92 | 99
Not designated as hedging instrument [Member] | Commodity derivatives [Member] |  |
Derivative instruments [Line Items] |  |
Amount of gain (loss) recognized in discontinued operations, before tax | $ 0 | $ (11,208)

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- Definition Amount of gain (loss) recognized in earnings in the period from the increase (decrease) in fair value of price risk derivatives not designated as hedging instruments. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=64837297&loc=SL5624171-113959 + Details
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- Definition Amount after tax of reclassification adjustment from accumulated other comprehensive income of accumulated gain (loss) realized from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's deferred hedging gain (loss). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=66004124&loc=d3e689-108580 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4 -Subparagraph c -URI http://asc.fasb.org/extlink&oid=64837297&loc=d3e41638-113959 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=66004124&loc=d3e637-108580 + Details
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