Derivative Instruments (Details 1) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Fair values of the derivative contracts recorded in the condensed consolidated balance sheet
Derivative Asset Fair Value Net	$ 585	$ 1,754
Derivatives liability not designated as hedging instruments	504	1,496
Mark to Market Energy Assets [Member] | Forward Contracts [Member]
Fair values of the derivative contracts recorded in the condensed consolidated balance sheet
Derivatives asset not designated as hedging instruments	462	1,686
Mark to Market Energy Assets [Member] | Put Option [Member] | Derivatives designated as fair value hedges [Member]
Fair values of the derivative contracts recorded in the condensed consolidated balance sheet
Derivative Asset Fair Value Net		68
Mark to Market Energy Assets [Member] | Call Option [Member] | Derivatives designated as fair value hedges [Member]
Fair values of the derivative contracts recorded in the condensed consolidated balance sheet
Derivative Asset Fair Value Net	123
Mark-to-market energy liabilities [Member] | Forward Contracts [Member]
Fair values of the derivative contracts recorded in the condensed consolidated balance sheet
Derivatives liability not designated as hedging instruments	$ 504	$ 1,496