Effect of Derivative Instruments on Financial Performance (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Aug. 31, 2012		Aug. 31, 2011		Aug. 31, 2010
Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in OCI	$ 3,734		$ (9,708)		$ (3,771)
Amount of Gain (Loss) Reclassified from AOCI into Income	2,271		(11,825)		(3,000)
Amount of Gain (Loss) Recognized in Income	36		(247)		(1,756)
Cash Flow Hedging [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in OCI					(395)	[1],[2]
Amount of Gain (Loss) Reclassified from AOCI into Income					(662)	[1],[2]
Amount of Gain (Loss) Recognized in Income					(1,562)	[1],[2]
Cash Flow Hedging [Member] | FX Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Reclassified from AOCI into Income					(26)	[3]
Cash Flow Hedging [Member] | Corn Futures [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in OCI	2,067	[3]	(4,949)	[3]	384	[3]
Amount of Gain (Loss) Reclassified from AOCI into Income	1,500	[3]	(7,418)	[3]	349	[3]
Amount of Gain (Loss) Recognized in Income	36	[3]	(162)	[3]	(194)	[3]
Cash Flow Hedging [Member] | Natural Gas Futures [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in OCI			(579)	[3]	(3,170)	[3]
Amount of Gain (Loss) Reclassified from AOCI into Income	(492)	[3]	(1,332)	[3]	(2,168)	[3]
Amount of Gain (Loss) Recognized in Income			(85)	[3]
Cash Flow Hedging [Member] | Ethanol Futures [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in OCI	1,667	[3]	(4,180)	[3]	(590)	[3]
Amount of Gain (Loss) Reclassified from AOCI into Income	1,263	[3]	(3,075)	[3]	(493)	[3]
Fair Value Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in Income	(1,078)
Fair Value Hedging [Member] | FX Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in Income	6	[3]
Fair Value Hedging [Member] | Soybean Oil Futures [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in Income	12	[3]
Fair Value Hedging [Member] | Soybean Meal Futures [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in Income	(14)	[3]
Fair Value Hedging [Member] | Corn Futures [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in Income	98	[3],[4]	28	[3],[4]	85	[3],[4]
Fair Value Hedging [Member] | Natural Gas Futures [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in Income	$ (1,082)	[3]

[1] Gains and losses reported in interest expense

[2] Amount of loss recognized in income was reported in non-operating income (expense)

[3] Gains and losses reported in cost of goods sold

[4] Hedged items are firm commitments and inventory