Fair Value Measurements and Derivative Instruments - Fair Values of Company's Derivatives (Detail) (Commodity Contract [Member], Other Current Assets [Member], USD $) In Thousands, unless otherwise specified	Aug. 31, 2012	Aug. 31, 2011
Commodity derivatives	$ (1,422)
Commodity derivatives		(3,153)
Level 1 [Member]
Commodity derivatives	(1,422)
Commodity derivatives	(3,153)
Level 2 [Member]
Commodity derivatives
Commodity derivatives
Level 3 [Member]
Commodity derivatives
Commodity derivatives