Equity Method Investments - Operating Results (Details) - Illinois Corn Processings LLC - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule of Equity Method Investments [Line Items]
Net sales	$ 78,062	$ 177,401	$ 166,905
Cost of sales and expenses	(79,224)	(163,837)	(146,098)
Net income	$ (1,162)	$ 13,564	$ 20,807