Quarterly Financial Data (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	May 31, 2013	Feb. 28, 2013	Nov. 30, 2012	Aug. 31, 2012	May 31, 2012	Feb. 29, 2012	Nov. 30, 2011	Aug. 31, 2011	May 31, 2013		May 31, 2012		May 31, 2011
Schedule Of Quarterly Financial Information [Line Items]
Total Revenues	$ 60,366	$ 64,672	$ 65,192	$ 58,501	$ 68,182	$ 60,079	$ 61,643	$ 58,650	$ 248,731	[1]	$ 248,554	[1]	$ 228,729	[1]
Gross Profit	24,684	22,160	24,388	22,022	24,125	20,883	22,588	21,740	93,254		89,336
Income Before Taxes	9,828	8,437	10,457	8,391	10,334	8,023	9,735	11,913	37,113		40,005		37,289
Net income	$ 6,392	$ 5,037	$ 6,239	$ 5,086	$ 6,253	$ 4,995	$ 6,019	$ 8,505	$ 22,754		$ 25,772		$ 23,756
Earnings Per Share Basic	$ 0.27	$ 0.21	$ 0.26	$ 0.21	$ 0.26	$ 0.21	$ 0.25	$ 0.35	$ 0.94		$ 1.07		$ 0.99
Earnings Per share Diluted	$ 0.26	$ 0.21	$ 0.26	$ 0.21	$ 0.26	$ 0.21	$ 0.25	$ 0.35	$ 0.94		$ 1.07		$ 0.99

[1] Revenues by country are based on the location of shipping destination, whether the order originates in the U.S. parent or a foreign subsidiary.