Income Taxes (Details) (USD $)	3 Months Ended		9 Months Ended		12 Months Ended		3 Months Ended			9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2009 Alternative Fuel Mixture Credit [Member]	Dec. 31, 2009 Cellulosic Biofuel Producer Credit [Member]	Sep. 30, 2012 Exchange of Alternative Fuel Tax Benefit [Member]	Jun. 30, 2012 Exchange of Alternative Fuel Tax Benefit [Member]	Sep. 30, 2011 Exchange of Alternative Fuel Tax Benefit [Member]	Sep. 30, 2012 Exchange of Alternative Fuel Tax Benefit [Member]	Sep. 30, 2011 Exchange of Alternative Fuel Tax Benefit [Member]	Sep. 30, 2011 Taxability of the Alternative Fuel Mixture Credit [Member]
Tax Credit Amount per Gallon					$ 0.50	$ 1.01
Gallons Exchanged	22 million gallons	11 million gallons	82 million	41 million
Income Tax Credits and Adjustments							(2,600,000)		(2,000,000)	(11,700,000)	(6,100,000)
Interest Expense	8,253,000	12,356,000	36,133,000	38,300,000			(3,400,000)	3,400,000
Income tax expense at federal statutory rate	37,000,000	34,000,000	91,000,000	83,000,000
U.S. federal statutory income tax rate	35.00%	35.00%	35.00%	35.00%
REIT income not subject to tax	(6,000,000)	(11,000,000)	(18,000,000)	(25,000,000)
REIT income not subject to tax, %	(5.70%)	(11.30%)	(7.00%)	(10.60%)
Other	(3,000,000)	(4,000,000)	(4,000,000)	(5,000,000)
Other, %	(2.90%)	(3.70%)	(1.60%)	(1.90%)
Income tax expense before non-routine items	28,000,000	19,000,000	69,000,000	53,000,000
Income tax expense before non-routine items, %	26.40%	20.00%	26.40%	22.50%
AFMC for CBPC exchange	(3,000,000)	(2,000,000)	(12,000,000)	(6,000,000)
AFMC for CBPC exchange, %	(3.00%)	(2.10%)	(4.50%)	(2.60%)
AFMC reserve reversal	0	(16,000,000)	0	(16,000,000)								(16,000,000)
AFMC reserve reversal, %	0.00%	(16.60%)	0.00%	(6.70%)
Installment note prepayment	0	(9,300,000)	0	(9,300,000)
Installment note prepayment, %	0.00%	(9.30%)	0.00%	(3.90%)
Built-in gains tax holiday	0	(1,000,000)	0	(4,000,000)
Built-in gains tax holiday, %	0.00%	(1.00%)	0.00%	(1.80%)
Income tax expense (benefit) as reported	$ 24,595,000	$ (8,624,000)	$ 56,859,000	$ 17,822,000
Income tax expense (benefit) as reported, %	23.40%	(9.00%)	21.90%	7.50%