Schedule of Derivatives Designated as Cash Flow Hedging Instruments (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Aug. 31, 2012	Aug. 31, 2011
Derivative [Line Items]
Gain (Loss) Recognized in OCI (Effective Portion)	$ (178)	$ (1,846)
Gain (Loss) Reclassified from Accumulated OCI (Effective Portion)	(1,402)	951
Gain (Loss) (Ineffective Portion) and Excluded from Effectiveness Testing
Interest Rate Contracts
Derivative [Line Items]
Gain (Loss) Recognized in OCI (Effective Portion)	(606)	(2,130)
Interest Rate Contracts | Interest Expense
Derivative [Line Items]
Gain (Loss) Reclassified from Accumulated OCI (Effective Portion)	(983)	(1,070)
Gain (Loss) (Ineffective Portion) and Excluded from Effectiveness Testing
Commodity Contracts
Derivative [Line Items]
Gain (Loss) Recognized in OCI (Effective Portion)	428	284
Commodity Contracts | Cost Of Goods Sold
Derivative [Line Items]
Gain (Loss) Reclassified from Accumulated OCI (Effective Portion)	(419)	2,021
Gain (Loss) (Ineffective Portion) and Excluded from Effectiveness Testing