Fair Value Measurements and Derivative Instruments - Fair Values of Company's Derivative Instruments (Detail) (Commodity Contract [Member], USD $) In Thousands, unless otherwise specified	Nov. 30, 2014	Aug. 31, 2014
Derivative [Line Items]
Commodity derivatives	$ (1,678)	$ (1,787)
Other Current Assets [Member]
Derivative [Line Items]
Commodity derivatives	(1,678)	(1,787)
Level 1 [Member] | Other Current Assets [Member]
Derivative [Line Items]
Commodity derivatives	(1,678)	(1,787)
Level 2 [Member] | Other Current Assets [Member]
Derivative [Line Items]
Commodity derivatives	0	0
Level 3 [Member] | Other Current Assets [Member]
Derivative [Line Items]
Commodity derivatives	$ 0	$ 0