Financial Instruments (Details 4) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2013	Mar. 31, 2012
Schedule of Realized and Unrealized Gains (Losses) from Commodity Derivatives
Realized and unrealized gains (losses) from commodity derivatives	$ (544)	$ (1,125)

Net Increase or Decrease in the fair value of the derivative or group of derivatives included in earnings.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4A

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5618551-113959

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Balance Type:	credit
Period Type:	duration