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Subsequent Events (Details) (USD $)
 1 Months Ended 12 Months Ended
Feb. 29, 2012
Jan. 31, 2012
Long Term Commitments [Member]
Dec. 31, 2011
Long Term Commitments [Member]
Jan. 31, 2012
Millions Of Barrels [Member]
Long Term Commitments [Member]
Subsequent Event [Line Items]        
Minimum quantity of delivery       4.4
Future obligations under supply agreements   $ 13,000,000 $ 54,500,000  
Number of barrels converted for deferred premium put contracts 1,000      
Selling price of costless collar in call option $ 111.30