Note 15 - 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, 2014		Feb. 28, 2013		Feb. 28, 2014		Feb. 28, 2013
Net sales to customers by geography are as follows:
Net sales to customers by geography	$ 90,979		$ 86,192		$ 287,226		$ 253,402
UNITED STATES
Net sales to customers by geography are as follows:
Net sales to customers by geography	55,240		57,690		177,722		167,944
Europe [Member]
Net sales to customers by geography are as follows:
Net sales to customers by geography	19,964	[1]	14,895	[1]	57,188	[1]	44,933	[1]
CANADA
Net sales to customers by geography are as follows:
Net sales to customers by geography	4,429		5,044		14,044		14,618
Other Geographic Area [Member]
Net sales to customers by geography are as follows:
Net sales to customers by geography	$ 11,346		$ 8,563		$ 38,272		$ 25,907

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