Schedule of Fair Value of Derivative Instruments (Detail) - USD ($) $ in Thousands	Aug. 31, 2016	May 31, 2016
Derivative [Line Items]
Asset Derivatives at Fair Value	$ 14,999	$ 21,790
Liability Derivatives at Fair Value	708	2,013
Derivatives Designated As Hedging Instruments
Derivative [Line Items]
Asset Derivatives at Fair Value	11,187	16,813
Liability Derivatives at Fair Value	526	1,237
Derivatives Designated As Hedging Instruments | Commodity Contracts
Derivative [Line Items]
Asset Derivatives at Fair Value	11,187	16,813
Liability Derivatives at Fair Value	31	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	10,337	13,224
Derivatives Designated As Hedging Instruments | Commodity Contracts | Other Assets
Derivative [Line Items]
Asset Derivatives at Fair Value	850	3,589
Derivatives Designated As Hedging Instruments | Commodity Contracts | Accounts Payable
Derivative [Line Items]
Liability Derivatives at Fair Value	31	696
Derivatives Designated As Hedging Instruments | Interest Rate Contracts
Derivative [Line Items]
Liability Derivatives at Fair Value	495	461
Derivatives Designated As Hedging Instruments | Interest Rate Contracts | Other Liabilities
Derivative [Line Items]
Liability Derivatives at Fair Value	320	306
Derivatives Designated As Hedging Instruments | Interest Rate Contracts | Accounts Payable
Derivative [Line Items]
Liability Derivatives at Fair Value	175	155
Derivatives Not Designated As Hedging Instruments
Derivative [Line Items]
Asset Derivatives at Fair Value	3,812	4,977
Liability Derivatives at Fair Value	182	776
Derivatives Not Designated As Hedging Instruments | Commodity Contracts
Derivative [Line Items]
Asset Derivatives at Fair Value	3,812	4,977
Liability Derivatives at Fair Value	151	761
Derivatives Not Designated As Hedging Instruments | Commodity Contracts | Receivables
Derivative [Line Items]
Asset Derivatives at Fair Value	3,737	4,660
Derivatives Not Designated As Hedging Instruments | Commodity Contracts | Other Assets
Derivative [Line Items]
Asset Derivatives at Fair Value	75	317
Derivatives Not Designated As Hedging Instruments | Commodity Contracts | Accounts Payable
Derivative [Line Items]
Liability Derivatives at Fair Value	151	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 | Accounts Payable
Derivative [Line Items]
Liability Derivatives at Fair Value	$ 31	$ 15