Note 16 - Segment and Geographic Information (Details) - Net Export Sales to Unaffiliated Customers - USD ($) $ in Thousands		3 Months Ended
		Aug. 31, 2015	Aug. 31, 2014
Net sales to customers by geography are as follows:
Net sales to customers by geography		$ 96,712	$ 102,441
UNITED STATES
Net sales to customers by geography are as follows:
Net sales to customers by geography		61,422	62,379
Europe [Member]
Net sales to customers by geography are as follows:
Net sales to customers by geography	[1]	17,787	21,447
CANADA
Net sales to customers by geography are as follows:
Net sales to customers by geography		3,899	4,891
Other Geographic Area [Member]
Net sales to customers by geography are as follows:
Net sales to customers by geography		$ 13,604	$ 13,724

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