Property Plant and Equipment - Additional Information (Detail) (USD $)	3 Months Ended	12 Months Ended
	May 31, 2012 acre	May 31, 2013	May 31, 2012 acre	May 31, 2011
Property, Plant, and Equipment Disclosure [Line Items]
Depreciation		$ 16,200,000	$ 14,900,000	$ 13,600,000
Asset write-off of costs capitalized	$ 1,700,000		$ 1,658,000
Purchase land planned to construct facilities in area	50		50