Income Taxes AFMC and CBPC Narrative (Details) (USD $) In Millions, unless otherwise specified		12 Months Ended
	Dec. 31, 2009 tax_credit	Dec. 31, 2009 Alternative Fuel Mixture Credit [Member]	Dec. 31, 2009 Cellulosic Biofuel Producer Credit [Member]	Dec. 31, 2013 Exchange of Alternative Fuel Tax Benefit [Member]	Dec. 31, 2012 Exchange of Alternative Fuel Tax Benefit [Member]	Dec. 31, 2011 Exchange of Alternative Fuel Tax Benefit [Member]
AFMC for CBPC Exchange [Line Items]
Number of tax credits	2
Tax credit amount per gallon		0.50	1.01
Income tax credits and adjustments				$ 18.8	$ 12.2	$ 5.8