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Derivative Instruments Gains and losses on derivative instruments (Details 2) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Derivative instruments [Line Items]
Amount of gain (loss) recognized in accumulated other comprehensive loss (effective portion), net of tax	$ 0	$ 0	$ (5,594)
Amount of (gain) loss reclassified from accumulated other comprehensive loss into discontinued operations (effective portion), net of tax	0	295	(4,916)
Amount of loss reclassified from accumulated other comprehensive loss into income statement (effective portion), net of tax	404	399	727
Designated as hedging instrument [Member] | Commodity derivatives designated as cash flow hedges [Member]
Derivative instruments [Line Items]
Amount of gain (loss) recognized in accumulated other comprehensive loss (effective portion), net of tax	0	0	(6,153)
Amount of (gain) loss reclassified from accumulated other comprehensive loss into discontinued operations (effective portion), net of tax	0	295	(4,916)
Amount of loss recognized in income statement (ineffective portion), before tax	0	0	(1,422)
Designated as hedging instrument [Member] | Interest rate derivatives designated as cash flow hedges [Member]
Derivative instruments [Line Items]
Amount of gain (loss) recognized in accumulated other comprehensive loss (effective portion), net of tax	0	0	559
Amount of loss reclassified from accumulated other comprehensive loss into income statement (effective portion), net of tax	404	399	727
Amount of loss recognized in income statement (ineffective portion), before tax	0	0	(769)
Not designated as hedging instruments [Member] | Commodity derivatives [Member]
Derivative instruments [Line Items]
Amount of gain (loss) recognized in discontinued operations, before tax	$ (18,335)	$ 23,400	$ (4,845)

X

- Definition

Amount after tax of reclassification adjustment from accumulated other comprehensive income for gain (loss) realized on derivative instruments included in income (loss) from discontinued operations, net of tax.

+ References

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- Definition

The net gain (loss) recognized in earnings during the reporting period representing the amount of the cash flow hedges' ineffectiveness.

+ 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 (d)(1)
-URI http://asc.fasb.org/extlink&oid=56946850&loc=SL5624171-113959

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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
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-Topic 815
-SubTopic 10
-Section 50
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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=36458714&loc=d3e689-108580

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Amount after tax of increase (decrease) in accumulated gain (loss) from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's increase (decrease) in deferred hedging gain (loss).

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-URI http://asc.fasb.org/extlink&oid=36458714&loc=SL7669646-108580

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