Derivative Financial Instruments - Outstanding Derivative Contracts Entered into Hedge Forecasted Purchases and Future Cash Receipts (Detail) (USD $) In Thousands, unless otherwise specified	Jul. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notional Amount	$ 104,681
Fair Value	3,424
Inventory Commodity [Member] | United States dollars [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notional Amount	100,549
Fair Value	3,181
Accounts receivable Commodity [Member] | British pounds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notional Amount	4,132
Fair Value	$ 243
Minimum [Member] | Inventory Commodity [Member] | United States dollars [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Maturity	2013-08
Minimum [Member] | Accounts receivable Commodity [Member] | British pounds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Maturity	2013-08
Maximum [Member] | Inventory Commodity [Member] | United States dollars [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Maturity	2014-10
Maximum [Member] | Accounts receivable Commodity [Member] | British pounds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Maturity	2013-10