Derivative Instruments (Detail)	1 Months Ended	12 Months Ended
	Feb. 29, 2012	Dec. 31, 2012	Sep. 30, 2013 Cash Flow Hedge [Member] derivative_contract
Derivative [Line Items]
Supply contract to purchase corn, maximum term		12 months
Percentage of derivatives no longer designated (percent)	100.00%
Number of derivative contracts (derivative contracts)			0