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Income Taxes - Additional Information (Detail) (USD $)
 12 Months Ended 3 Months Ended 12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2012
Federal
Dec. 31, 2012
State
Dec. 31, 2012
Cellulosic Biofuel Tax Credits
Mar. 31, 2012
Cellulosic Biofuel Tax Credits
Dec. 31, 2010
Cellulosic Biofuel Tax Credits
Dec. 31, 2012
Cellulosic Biofuel Tax Credits
Federal
Period 1
Dec. 31, 2012
Cellulosic Biofuel Tax Credits
Federal
Period 2
Dec. 31, 2012
Alternative Energy Tax Credits
Schedule Of Income Taxes [Line Items]                      
Alternative fuel mixture and cellulosic biofuel producer credits $ (81,695,000)   $ 104,785,000                
Tax reserve on uncertain tax positions 111,303,000 111,013,000 112,311,000         102,000,000      
Income tax expense (benefit) 216,739,000 85,477,000 (52,331,000)     3,400,000 (118,500,000) 135,500,000     81,700,000
Cash payments for income taxes 9,700,000 52,700,000 19,100,000                
Decrease uncertain tax positions, gross 1,100,000                    
Decrease uncertain tax positions, net 700,000                    
Unrecognized tax benefits that would impact of effective tax rate 107,000,000                    
Income tax, interest expense gross 300,000 200,000                  
Income tax, interest expense net 200,000 160,000                  
Income tax, accrued interest expense gross 2,500,000 2,200,000                  
Income tax, accrued interest expense net 1,600,000 1,400,000                  
Income tax, accrual for penalties 100,000                    
Income tax examination, year of examination       Federal examination of the tax years 2002 and 2004 has been concluded. The tax years 2008 - 2012 remain open to federal examination. The tax years 2002 - 2012 remain open to state examinations            
Income tax examination, year of examination                 2009 2008  
Change in uncertain tax positions, minimum 0                    
Change in uncertain tax positions, maximum $ 105,000,000