Schedule of Fair Value of Derivative Instruments (Detail) - USD ($) $ in Thousands	Nov. 30, 2016	May 31, 2016
Derivative [Line Items]
Asset Derivatives at Fair Value	$ 20,612	$ 21,790
Liability Derivatives at Fair Value	956	2,013
Derivatives Designated As Hedging Instruments
Derivative [Line Items]
Asset Derivatives at Fair Value	15,908	16,813
Liability Derivatives at Fair Value	825	1,237
Derivatives Designated As Hedging Instruments | Commodity Contracts
Derivative [Line Items]
Asset Derivatives at Fair Value	15,908	16,813
Liability Derivatives at Fair Value	489	776
Derivatives Designated As Hedging Instruments | Commodity Contracts | Other Liabilities
Derivative [Line Items]
Liability Derivatives at Fair Value		80
Derivatives Designated As Hedging Instruments | Commodity Contracts | Receivables
Derivative [Line Items]
Asset Derivatives at Fair Value	15,807	13,224
Derivatives Designated As Hedging Instruments | Commodity Contracts | Other Assets
Derivative [Line Items]
Asset Derivatives at Fair Value	101	3,589
Derivatives Designated As Hedging Instruments | Commodity Contracts | Accounts Payable
Derivative [Line Items]
Liability Derivatives at Fair Value	489	696
Derivatives Designated As Hedging Instruments | Interest Rate Contracts
Derivative [Line Items]
Liability Derivatives at Fair Value	336	461
Derivatives Designated As Hedging Instruments | Interest Rate Contracts | Other Liabilities
Derivative [Line Items]
Liability Derivatives at Fair Value	195	306
Derivatives Designated As Hedging Instruments | Interest Rate Contracts | Accounts Payable
Derivative [Line Items]
Liability Derivatives at Fair Value	141	155
Derivatives Not Designated As Hedging Instruments
Derivative [Line Items]
Asset Derivatives at Fair Value	4,704	4,977
Liability Derivatives at Fair Value	131	776
Derivatives Not Designated As Hedging Instruments | Commodity Contracts
Derivative [Line Items]
Asset Derivatives at Fair Value	4,190	4,977
Liability Derivatives at Fair Value	131	761
Derivatives Not Designated As Hedging Instruments | Commodity Contracts | Receivables
Derivative [Line Items]
Asset Derivatives at Fair Value	4,149	4,660
Derivatives Not Designated As Hedging Instruments | Commodity Contracts | Other Assets
Derivative [Line Items]
Asset Derivatives at Fair Value	41	317
Derivatives Not Designated As Hedging Instruments | Commodity Contracts | Accounts Payable
Derivative [Line Items]
Liability Derivatives at Fair Value	131	761
Derivatives Not Designated As Hedging Instruments | Foreign Currency Contracts
Derivative [Line Items]
Liability Derivatives at Fair Value		15
Derivatives Not Designated As Hedging Instruments | Foreign Currency Contracts | Receivables
Derivative [Line Items]
Asset Derivatives at Fair Value	$ 514
Derivatives Not Designated As Hedging Instruments | Foreign Currency Contracts | Accounts Payable
Derivative [Line Items]
Liability Derivatives at Fair Value		$ 15