Income Taxes (Details) (USD $)	3 Months Ended		6 Months Ended		12 Months Ended		3 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2009 Alternative Fuel Mixture Credit [Member]	Dec. 31, 2009 Cellulosic Biofuel Producer Credit [Member]	Jun. 30, 2012 Exchange of Alternative Fuel Tax Benefit [Member]	Jun. 30, 2011 Exchange of Alternative Fuel Tax Benefit [Member]
U.S. federal statutory income tax rate			35.00%
Effective tax rate	16.40%	15.40%	20.80%	18.70%
Tax Credit Amount per Gallon					$ 0.50	$ 1.01
Gallons Exchanged	60 million gallons	30 million gallons
Net Benefit of Exchange	5,700,000
Income Tax Benefit							9,100,000	4,100,000
Interest Expense	$ 16,056,000	$ 12,628,000	$ 27,880,000	$ 25,945,000			$ 3,400,000