Goodwill and Other Intangible Assets - Additional Information (Detail) (USD $)	12 Months Ended
	May 31, 2012	May 31, 2011	May 31, 2010
Goodwill And Other Intangible Assets [Line Items]
Amortization expense	$ 5,229,000	$ 3,293,000	$ 4,124,000
Minimum
Goodwill And Other Intangible Assets [Line Items]
Definite-lived intangible assets, estimated useful lives	1 year
Maximum
Goodwill And Other Intangible Assets [Line Items]
Definite-lived intangible assets, estimated useful lives	20 years