Schedule of Fair Value of Derivative Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Aug. 31, 2013	May 31, 2013
Derivative [Line Items]
Asset Derivatives at Fair Value	$ 3,183	$ 761
Liability Derivatives at Fair Value	6,313	9,774
Derivatives Designated As Hedging Instruments
Derivative [Line Items]
Asset Derivatives at Fair Value	2,305	425
Liability Derivatives at Fair Value	6,029	9,247
Derivatives Designated As Hedging Instruments | Interest Rate Contracts
Derivative [Line Items]
Liability Derivatives at Fair Value	6,029	7,895
Derivatives Designated As Hedging Instruments | Interest Rate Contracts | Other Liabilities
Derivative [Line Items]
Liability Derivatives at Fair Value	1,916	3,863
Derivatives Designated As Hedging Instruments | Interest Rate Contracts | Accounts Payable
Derivative [Line Items]
Liability Derivatives at Fair Value	4,113	4,032
Derivatives Designated As Hedging Instruments | Commodity Contracts
Derivative [Line Items]
Asset Derivatives at Fair Value	2,305	425
Liability Derivatives at Fair Value		1,352
Derivatives Designated As Hedging Instruments | Commodity Contracts | Receivables
Derivative [Line Items]
Asset Derivatives at Fair Value	2,305	425
Derivatives Designated As Hedging Instruments | Commodity Contracts | Accounts Payable
Derivative [Line Items]
Liability Derivatives at Fair Value		1,352
Derivatives Not Designated As Hedging Instruments
Derivative [Line Items]
Asset Derivatives at Fair Value		336
Liability Derivatives at Fair Value		527
Derivatives Not Designated As Hedging Instruments | Commodity Contracts
Derivative [Line Items]
Asset Derivatives at Fair Value	878	331
Liability Derivatives at Fair Value	284	527
Derivatives Not Designated As Hedging Instruments | Commodity Contracts | Receivables
Derivative [Line Items]
Asset Derivatives at Fair Value	878	331
Derivatives Not Designated As Hedging Instruments | Commodity Contracts | Accounts Payable
Derivative [Line Items]
Liability Derivatives at Fair Value	284	527
Derivatives Not Designated As Hedging Instruments | Foreign Exchange Contracts
Derivative [Line Items]
Asset Derivatives at Fair Value		5
Derivatives Not Designated As Hedging Instruments | Foreign Exchange Contracts | Receivables
Derivative [Line Items]
Asset Derivatives at Fair Value		$ 5