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Alternative Energy Tax Credits (Details) (USD $)
 3 Months Ended 3 Months Ended 12 Months Ended 24 Months Ended 3 Months Ended 12 Months Ended 3 Months Ended
Mar. 31, 2010
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2010
Alternative Fuel Mixture Credits [Member]
Sep. 30, 2010
Alternative Fuel Mixture Credits [Member]
Dec. 31, 2011
Alternative Fuel Mixture Credits [Member]
Dec. 31, 2009
Alternative Fuel Mixture Credits [Member]
Dec. 31, 2009
Alternative Fuel Mixture Credits [Member]
Dec. 31, 2010
Cellulosic Biofuel Tax Credits [Member]
Sep. 30, 2010
Cellulosic Biofuel Tax Credits [Member]
Dec. 31, 2011
Cellulosic Biofuel Tax Credits [Member]
Jun. 30, 2010
Cellulosic Biofuel Tax Credits [Member]
Dec. 31, 2010
Amended 2009 Federal Return [Member]
Alternative Energy Tax Credits [Line Items]                          
Refundable tax credit per gallon             $ 0.50 $ 0.50       $ 1.01  
Alternative fuels produced claimed for alternative energy tax credits           33.00%         66.00%    
Alternative fuel mixture released reserve 9,200,000                        
Increase in net income due to reserve release 9,200,000                        
Additional expenses                   800,000      
Additional expenses, net of tax                   500,000      
Cellulosic biofuel producer credits                         107,000,000
Alternative energy tax credits       16,400,000 (111,900,000)     185,400,000 5,000,000 33,400,000      
Alternative fuel mixture credits             185,400,000            
Cellulosic biofuel tax credit income impact                   145,800,000      
Uncertain tax positions     102,000,000                    
Tax credits used to offset future cash tax payment   $ 167,500,000