Changes in Accrued Warranty Balances (Detail) (USD $) In Thousands	3 Months Ended
	Aug. 31, 2011		Aug. 31, 2010
Loss Contingencies [Line Items]
Beginning Balance	$ 17,196		$ 17,602
Deductions	(4,072)	[1]	(5,812)	[1]
Provision charged to SG&A expense	3,841		4,150
Ending Balance	$ 16,965		$ 15,940

[1] Primarily claims paid during the year.