Schedule of Fair Value of Derivative Instruments (Detail) - USD ($) $ in Thousands	Aug. 31, 2015	May. 31, 2015
Derivative [Line Items]
Asset Derivatives at Fair Value	$ 11	$ 171
Liability Derivatives at Fair Value	22,112	22,131
Derivatives Designated As Hedging Instruments
Derivative [Line Items]
Asset Derivatives at Fair Value		75
Liability Derivatives at Fair Value	17,141	18,027
Derivatives Designated As Hedging Instruments | Commodity Contracts
Derivative [Line Items]
Liability Derivatives at Fair Value	16,981	17,833
Derivatives Designated As Hedging Instruments | Commodity Contracts | Other Liabilities
Derivative [Line Items]
Liability Derivatives at Fair Value	424	592
Derivatives Designated As Hedging Instruments | Commodity Contracts | Accounts Payable
Derivative [Line Items]
Liability Derivatives at Fair Value	16,557	17,241
Derivatives Designated As Hedging Instruments | Interest Rate Contracts
Derivative [Line Items]
Liability Derivatives at Fair Value	160	194
Derivatives Designated As Hedging Instruments | Interest Rate Contracts | Other Liabilities
Derivative [Line Items]
Liability Derivatives at Fair Value	79	113
Derivatives Designated As Hedging Instruments | Interest Rate Contracts | Accounts Payable
Derivative [Line Items]
Liability Derivatives at Fair Value	81	81
Derivatives Designated As Hedging Instruments | Foreign Exchange Contracts | Receivables
Derivative [Line Items]
Asset Derivatives at Fair Value		75
Derivatives Not Designated As Hedging Instruments
Derivative [Line Items]
Asset Derivatives at Fair Value	11	96
Liability Derivatives at Fair Value	4,971	4,104
Derivatives Not Designated As Hedging Instruments | Commodity Contracts
Derivative [Line Items]
Liability Derivatives at Fair Value	4,971
Derivatives Not Designated As Hedging Instruments | Commodity Contracts | Other Liabilities
Derivative [Line Items]
Liability Derivatives at Fair Value	119
Derivatives Not Designated As Hedging Instruments | Commodity Contracts | Receivables
Derivative [Line Items]
Asset Derivatives at Fair Value		96
Derivatives Not Designated As Hedging Instruments | Commodity Contracts | Accounts Payable
Derivative [Line Items]
Liability Derivatives at Fair Value	4,852	$ 4,104
Derivatives Not Designated As Hedging Instruments | Foreign Exchange Contracts
Derivative [Line Items]
Asset Derivatives at Fair Value	11
Derivatives Not Designated As Hedging Instruments | Foreign Exchange Contracts | Receivables
Derivative [Line Items]
Asset Derivatives at Fair Value	$ 11