Schedule of Fair Value of Derivative Instruments (Detail) - USD ($) $ in Thousands	Aug. 31, 2017	May 31, 2017
Derivative [Line Items]
Asset Derivatives at Fair Value	$ 9,079	$ 8,326
Liability Derivatives at Fair Value	342	1,142
Derivatives Designated As Hedging Instruments
Derivative [Line Items]
Asset Derivatives at Fair Value	6,539	7,154
Liability Derivatives at Fair Value	300	571
Derivatives Designated As Hedging Instruments | Commodity Contracts
Derivative [Line Items]
Asset Derivatives at Fair Value	6,539	7,154
Liability Derivatives at Fair Value		270
Derivatives Designated As Hedging Instruments | Commodity Contracts | Receivables
Derivative [Line Items]
Asset Derivatives at Fair Value	6,282	7,148
Derivatives Designated As Hedging Instruments | Commodity Contracts | Other Assets
Derivative [Line Items]
Asset Derivatives at Fair Value	257	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	300	301
Derivatives Designated As Hedging Instruments | Interest Rate Contracts | Other Liabilities
Derivative [Line Items]
Liability Derivatives at Fair Value	150	160
Derivatives Designated As Hedging Instruments | Interest Rate Contracts | Accounts Payable
Derivative [Line Items]
Liability Derivatives at Fair Value	150	141
Derivatives Not Designated As Hedging Instruments
Derivative [Line Items]
Asset Derivatives at Fair Value	2,540	1,172
Liability Derivatives at Fair Value	42	571
Derivatives Not Designated As Hedging Instruments | Commodity Contracts
Derivative [Line Items]
Asset Derivatives at Fair Value	2,540	1,110
Liability Derivatives at Fair Value	37	571
Derivatives Not Designated As Hedging Instruments | Commodity Contracts | Receivables
Derivative [Line Items]
Asset Derivatives at Fair Value	2,508	1,110
Derivatives Not Designated As Hedging Instruments | Commodity Contracts | Other Assets
Derivative [Line Items]
Asset Derivatives at Fair Value	32
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	37	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	$ 5