Note 16 - Segment and Geographic Information (Details) - Net Export Sales to Unaffiliated Customers (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Feb. 28, 2015		Feb. 28, 2014		Feb. 28, 2015		Feb. 28, 2014
Net sales to customers by geography are as follows:
Net sales to customers by geography	$ 95,605		$ 90,979		$ 294,323		$ 287,226
UNITED STATES
Net sales to customers by geography are as follows:
Net sales to customers by geography	60,205		55,240		179,679		177,722
Europe [Member]
Net sales to customers by geography are as follows:
Net sales to customers by geography	18,313	[1]	19,964	[1]	59,882	[1]	57,188	[1]
CANADA
Net sales to customers by geography are as follows:
Net sales to customers by geography	4,598		4,429		14,200		14,044
Other Geographic Area [Member]
Net sales to customers by geography are as follows:
Net sales to customers by geography	$ 12,489		$ 11,346		$ 40,562		$ 38,272

[1] Net sales to any individual country within Europe were not material to the Company's consolidated net sales.