Investment In And Loans To Dynamic Fuels (Narrative) (Details) (USD $)	3 Months Ended			12 Months Ended	3 Months Ended
	Mar. 31, 2013 gal	Mar. 31, 2012	Dec. 31, 2012	Dec. 31, 2012 Dynamic Fuels, LLC [Member]	Mar. 31, 2013 Tyson Foods, Inc [Member]
Unusual Risk or Uncertainty [Line Items]
Equity investment in and loans to Dynamic Fuels, LLC	$ 41,798,000		$ 38,407,000
Current accounts receivable from Dynamic Fuels, LLC	85,000		252,000
Excess value of investment in Dynamic Fuels, LLC	8,000,000
Tax credit per gallon of produced renewable diesel	1.00
Tax credit per gallon of produced alternative fuels	0.50
Diesel and renewable naphtha revenue	12,600,000			25,200,000
Tax refund, receivable	8,986,000
Working capital loan	4,000,000				4,000,000
Additional equity contribution to joint venture	1,700,000				1,700,000
Estimated working capital required to restart plant	20,000,000
Renewable products sold	66,800,000
Plant design production rate per year	75,000,000
Technical services revenue from Dynamic Fuels, LLC	417,000	379,000
Royalties from Dynamic Fuels, LLC plant production	$ 0	$ 240,000