Income Taxes - AFMC and CBPC - Narrative (Details) (USD $)	12 Months Ended
	Dec. 31, 2009	Dec. 31, 2014	Dec. 31, 2013		Dec. 31, 2012
AFMC for CBPC Exchange [Line Items]
Number of tax credits	2
Valuation allowance		$ 13,644,000	$ 33,889,000	[1]
Alternative Fuel Mixture Credit [Member]
AFMC for CBPC Exchange [Line Items]
Tax credit amount per gallon	0.50
Cellulosic Biofuel Producer Credit [Member]
AFMC for CBPC Exchange [Line Items]
Tax credit amount per gallon	1.01
Valuation allowance		13,600,000
Exchange of Alternative Fuel Tax Benefit [Member]
AFMC for CBPC Exchange [Line Items]
Net tax benefit from AFMC for CBPC exchange		$ 18,800,000	$ 12,200,000		$ 5,800,000

[1] Includes balances related to discontinued operations.