Schedule of Derivatives Designated as Cash Flow Hedging Instruments (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Feb. 28, 2013	Feb. 29, 2012	Feb. 28, 2013	Feb. 29, 2012
Derivative [Line Items]
Income (Loss) Recognized in OCI (Effective Portion)	$ (76)	$ (112)	$ (107)	$ (2,408)
Income (Loss) Reclassified from Accumulated OCI (Effective Portion)	(800)	(784)	(2,608)	(1,047)
Income (Loss) (Ineffective Portion) and Excluded from Effectiveness Testing
Interest Rate Contracts
Derivative [Line Items]
Income (Loss) Recognized in OCI (Effective Portion)	(389)	(571)	(878)	(2,444)
Interest Rate Contracts | Interest Expense
Derivative [Line Items]
Income (Loss) Reclassified from Accumulated OCI (Effective Portion)	(1,320)	(1,042)	(2,968)	(3,040)
Income (Loss) (Ineffective Portion) and Excluded from Effectiveness Testing
Commodity Contracts
Derivative [Line Items]
Income (Loss) Recognized in OCI (Effective Portion)	313	459	771	36
Commodity Contracts | Cost Of Goods Sold
Derivative [Line Items]
Income (Loss) Reclassified from Accumulated OCI (Effective Portion)	520	258	360	1,993
Income (Loss) (Ineffective Portion) and Excluded from Effectiveness Testing