Fair Value Measurements and Derivative Instruments - Fair Value of Companys Derivatives (Detail) (Other Current Assets [Member], Commodity Contract [Member], USD $) In Thousands, unless otherwise specified	Nov. 30, 2012		Aug. 31, 2012
Derivative [Line Items]
Commodity derivatives	$ (407)	[1]	$ (1,422)	[2]
Level 1 [Member]
Derivative [Line Items]
Commodity derivatives	(407)	[1]	(1,422)	[2]
Level 2 [Member]
Derivative [Line Items]
Commodity derivatives		[1]		[2]
Level 3 [Member]
Derivative [Line Items]
Commodity derivatives		[1]		[2]

[1] On the consolidated balance sheet, commodity derivative assets and liabilities have been offset by cash collateral due and paid under master netting arrangements which are recorded together in Other Current Assets. The cash collateral offset was $1.5 million at November 30, 2012.

[2] On the consolidated balance sheet, commodity derivative assets and liabilities have been offset by cash collateral due and paid under master netting arrangements which are recorded together in Other Current Assets. The cash collateral offset was $2.6 million at August 31, 2012.