Fair Value Measurements and Derivative Instruments - Effect of Derivative Instruments on Company's Financial Performance (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended				6 Months Ended
	Feb. 28, 2013		Feb. 29, 2012		Feb. 28, 2013		Feb. 29, 2012
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in Income	$ 89		$ (315)		$ (82)		$ (1,027)
Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in OCI	(85)		840		413		400
Amount of Gain (Loss) Reclassified from AOCI into Income	250		581		3,775		1,549
Amount of Gain (Loss) Recognized in Income	(312)		132		(126)		(179)
Cash Flow Hedging [Member] | Corn Futures [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in OCI	(318)	[1]	858	[1]	(573)	[1]	(750)	[1]
Amount of Gain (Loss) Reclassified from AOCI into Income	59	[1]	(130)	[1]	3,491	[1]	1,944	[1]
Amount of Gain (Loss) Recognized in Income	(312)	[1]	132	[1]	(115)	[1]	(179)	[1]
Cash Flow Hedging [Member] | Natural Gas Futures [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in OCI		[1]		[1]		[1]		[1]
Amount of Gain (Loss) Reclassified from AOCI into Income		[1]	(181)	[1]		[1]	(453)	[1]
Amount of Gain (Loss) Recognized in Income		[1]		[1]		[1]		[1]
Cash Flow Hedging [Member] | Ethanol Futures [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in OCI	233	[1]	(18)	[1]	986	[1]	1,150	[1]
Amount of Gain (Loss) Reclassified from AOCI into Income	191	[1]	892	[1]	284	[1]	58	[1]
Amount of Gain (Loss) Recognized in Income		[1]		[1]	(11)	[1]		[1]
Fair Value Hedging [Member] | Corn Futures [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in Income	(31)	[1],[2]	(21)	[1],[2]	(16)	[1],[2]	78	[1],[2]
Fair Value Hedging [Member] | Natural Gas Futures [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in Income	89	[1]	(336)	[1]	(82)	[1]	(1,048)	[1]
Fair Value Hedging [Member] | FX Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in Income		[2]	9	[2]		[2]	9	[2]
Fair Value Hedging [Member] | Soybean Oil Futures [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in Income		[1]	$ 12	[1]		[1]	$ 12	[1]

[1] Gains and losses reported in cost of sales

[2] Hedged items are firm commitments and inventory