Note 17 - Net Export Sales to Unaffiliated Customers (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Feb. 29, 2016	Feb. 28, 2015	Feb. 29, 2016	Feb. 28, 2015
UNITED STATES
Net sales to customers by geography are as follows:
Net Sales by product group		$ 57,435	$ 60,205	$ 179,878	$ 179,679
Europe [Member]
Net sales to customers by geography are as follows:
Net Sales by product group	[1]	16,609	18,313	52,517	59,882
CANADA
Net sales to customers by geography are as follows:
Net Sales by product group		3,233	4,598	11,084	14,200
Other Georgraphic Area [Member]
Net sales to customers by geography are as follows:
Net Sales by product group		11,616	12,489	38,375	40,562
Net Sales by product group		$ 88,893	$ 95,605	$ 281,854	$ 294,323

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