Schedule of Fair Value of Derivative Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Nov. 30, 2012	May 31, 2012
Derivative [Line Items]
Asset Derivatives at Fair Value	$ 904	$ 1,157
Liability Derivatives at Fair Value	10,559	14,993
Derivatives Designated As Hedging Instruments
Derivative [Line Items]
Asset Derivatives at Fair Value	509
Liability Derivatives at Fair Value	9,619	10,933
Derivatives Designated As Hedging Instruments | Interest Rate Contracts
Derivative [Line Items]
Liability Derivatives at Fair Value	9,619	10,684
Derivatives Designated As Hedging Instruments | Interest Rate Contracts | Accounts Payable
Derivative [Line Items]
Liability Derivatives at Fair Value	1,882	1,859
Derivatives Designated As Hedging Instruments | Interest Rate Contracts | Other Liabilities
Derivative [Line Items]
Liability Derivatives at Fair Value	7,737	8,825
Derivatives Designated As Hedging Instruments | Commodity Contracts
Derivative [Line Items]
Asset Derivatives at Fair Value	509
Liability Derivatives at Fair Value		249
Derivatives Designated As Hedging Instruments | Commodity Contracts | Accounts Payable
Derivative [Line Items]
Liability Derivatives at Fair Value		249
Derivatives Designated As Hedging Instruments | Commodity Contracts | Receivables
Derivative [Line Items]
Asset Derivatives at Fair Value	509
Derivatives Not Designated As Hedging Instruments
Derivative [Line Items]
Asset Derivatives at Fair Value	395	1,157
Liability Derivatives at Fair Value	940	4,060
Derivatives Not Designated As Hedging Instruments | Commodity Contracts
Derivative [Line Items]
Asset Derivatives at Fair Value	395	245
Liability Derivatives at Fair Value	662	4,060
Derivatives Not Designated As Hedging Instruments | Commodity Contracts | Accounts Payable
Derivative [Line Items]
Liability Derivatives at Fair Value	662	4,060
Derivatives Not Designated As Hedging Instruments | Commodity Contracts | Receivables
Derivative [Line Items]
Asset Derivatives at Fair Value	395	245
Derivatives Not Designated As Hedging Instruments | Foreign Exchange Contracts
Derivative [Line Items]
Asset Derivatives at Fair Value		912
Liability Derivatives at Fair Value	278
Derivatives Not Designated As Hedging Instruments | Foreign Exchange Contracts | Accounts Payable
Derivative [Line Items]
Liability Derivatives at Fair Value	278
Derivatives Not Designated As Hedging Instruments | Foreign Exchange Contracts | Receivables
Derivative [Line Items]
Asset Derivatives at Fair Value		$ 912