Fair Value Measurements and Derivative Instruments - Fair Values of Company's Derivative Instruments (Detail) (Commodity Contract [Member], USD $)
In Thousands, unless otherwise specified
May 31, 2014
Aug. 31, 2013
Derivative [Line Items]    
Commodity derivatives $ (2,899) $ 512
Other current assets [Member]
   
Derivative [Line Items]    
Commodity derivatives (2,899) 512
Level 1 [Member] | Other current assets [Member]
   
Derivative [Line Items]    
Commodity derivatives (2,899) 512
Level 2 [Member] | Other current assets [Member]
   
Derivative [Line Items]    
Commodity derivatives      
Level 3 [Member] | Other current assets [Member]
   
Derivative [Line Items]    
Commodity derivatives