Quarterly report pursuant to Section 13 or 15(d)

Derivative Instruments and Risk Management Activities (Details 6)

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Derivative Instruments and Risk Management Activities (Details 6) (Commodity derivative, USD $)
In Thousands, unless otherwise specified
Sep. 30, 2013
Dec. 31, 2012
Commodity derivative
   
Commodity derivative assets    
Gross amounts of recognized assets $ 715,960 $ 597,359
Gross amounts offset on balance sheet (7,437) (65,344)
Net amounts of assets on balance sheet 708,214 532,015
Commodity derivative liabilities    
Gross amounts offset on balance sheet (309)  
Net amounts of assets (liabilities) on balance sheet $ (309)