Schedule of Fair Value of Derivative Instruments (Detail) - USD ($) $ in Thousands	Nov. 30, 2017	May 31, 2017
Derivative [Line Items]
Asset Derivatives at Fair Value	$ 6,080	$ 8,326
Liability Derivatives at Fair Value	631	1,142
Derivatives Designated As Hedging Instruments
Derivative [Line Items]
Asset Derivatives at Fair Value	4,370	7,154
Liability Derivatives at Fair Value	265	571
Derivatives Designated As Hedging Instruments | Commodity Contracts
Derivative [Line Items]
Asset Derivatives at Fair Value	4,370	7,154
Liability Derivatives at Fair Value		270
Derivatives Designated As Hedging Instruments | Commodity Contracts | Receivables
Derivative [Line Items]
Asset Derivatives at Fair Value	3,721	7,148
Derivatives Designated As Hedging Instruments | Commodity Contracts | Other Assets
Derivative [Line Items]
Asset Derivatives at Fair Value	649	6
Derivatives Designated As Hedging Instruments | Commodity Contracts | Other Liabilities
Derivative [Line Items]
Liability Derivatives at Fair Value		159
Derivatives Designated As Hedging Instruments | Commodity Contracts | Accounts Payable
Derivative [Line Items]
Liability Derivatives at Fair Value		111
Derivatives Designated As Hedging Instruments | Interest Rate Contracts
Derivative [Line Items]
Liability Derivatives at Fair Value	265	301
Derivatives Designated As Hedging Instruments | Interest Rate Contracts | Other Liabilities
Derivative [Line Items]
Liability Derivatives at Fair Value	25	160
Derivatives Designated As Hedging Instruments | Interest Rate Contracts | Accounts Payable
Derivative [Line Items]
Liability Derivatives at Fair Value	240	141
Derivatives Not Designated As Hedging Instruments
Derivative [Line Items]
Asset Derivatives at Fair Value	1,710	1,172
Liability Derivatives at Fair Value	366	571
Derivatives Not Designated As Hedging Instruments | Commodity Contracts
Derivative [Line Items]
Asset Derivatives at Fair Value	1,710	1,110
Liability Derivatives at Fair Value	320	571
Derivatives Not Designated As Hedging Instruments | Commodity Contracts | Receivables
Derivative [Line Items]
Asset Derivatives at Fair Value	1,692	1,110
Derivatives Not Designated As Hedging Instruments | Commodity Contracts | Other Assets
Derivative [Line Items]
Asset Derivatives at Fair Value	18
Derivatives Not Designated As Hedging Instruments | Commodity Contracts | Other Liabilities
Derivative [Line Items]
Liability Derivatives at Fair Value		1
Derivatives Not Designated As Hedging Instruments | Commodity Contracts | Accounts Payable
Derivative [Line Items]
Liability Derivatives at Fair Value	320	570
Derivatives Not Designated As Hedging Instruments | Foreign Currency Contracts | Receivables
Derivative [Line Items]
Asset Derivatives at Fair Value		$ 62
Derivatives Not Designated As Hedging Instruments | Foreign Currency Contracts | Accounts Payable
Derivative [Line Items]
Liability Derivatives at Fair Value	$ 46