Derivative Financial Instruments - Outstanding Derivative Contracts Entered into Hedge Forecasted Purchases (Detail) (Inventory Commodity [Member], United States Dollars [Member], USD $) In Thousands, unless otherwise specified	Jul. 31, 2014
Inventory Commodity [Member] | United States Dollars [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notional Amount	$ 286,032
Fair Value	$ 3,063