Schedule of Fair Value of Derivative Instruments (Detail) - USD ($) $ in Thousands	Feb. 29, 2016	May. 31, 2015
Derivative [Line Items]
Asset Derivatives at Fair Value		$ 171
Liability Derivatives at Fair Value	$ 15,522	22,131
Derivatives Designated As Hedging Instruments
Derivative [Line Items]
Asset Derivatives at Fair Value		75
Liability Derivatives at Fair Value	13,140	18,027
Derivatives Designated As Hedging Instruments | Commodity Contracts
Derivative [Line Items]
Liability Derivatives at Fair Value	12,672	17,833
Derivatives Designated As Hedging Instruments | Commodity Contracts | Other Liabilities
Derivative [Line Items]
Liability Derivatives at Fair Value	338	592
Derivatives Designated As Hedging Instruments | Commodity Contracts | Accounts Payable
Derivative [Line Items]
Liability Derivatives at Fair Value	12,334	17,241
Derivatives Designated As Hedging Instruments | Interest Rate Contracts
Derivative [Line Items]
Liability Derivatives at Fair Value	468	194
Derivatives Designated As Hedging Instruments | Interest Rate Contracts | Other Liabilities
Derivative [Line Items]
Liability Derivatives at Fair Value	327	113
Derivatives Designated As Hedging Instruments | Interest Rate Contracts | Accounts Payable
Derivative [Line Items]
Liability Derivatives at Fair Value	141	81
Derivatives Designated As Hedging Instruments | Foreign Currency 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		96
Liability Derivatives at Fair Value	2,382	4,104
Derivatives Not Designated As Hedging Instruments | Commodity Contracts
Derivative [Line Items]
Liability Derivatives at Fair Value	2,380
Derivatives Not Designated As Hedging Instruments | Commodity Contracts | Other Liabilities
Derivative [Line Items]
Liability Derivatives at Fair Value	133
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	2,247	$ 4,104
Derivatives Not Designated As Hedging Instruments | Foreign Currency Contracts
Derivative [Line Items]
Liability Derivatives at Fair Value	2
Derivatives Not Designated As Hedging Instruments | Foreign Currency Contracts | Accounts Payable
Derivative [Line Items]
Liability Derivatives at Fair Value	$ 2