Note 16 - Net Export Sales to Unaffiliated Customers (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Nov. 30, 2015	Nov. 30, 2014	Nov. 30, 2015	Nov. 30, 2014
UNITED STATES
Net sales to customers by geography are as follows:
Net Sales by product group		$ 61,024	$ 57,099	$ 122,426	$ 119,612
Europe [Member]
Net sales to customers by geography are as follows:
Net Sales by product group	[1]	18,119	20,122	35,919	41,569
CANADA
Net sales to customers by geography are as follows:
Net Sales by product group		3,952	4,711	7,851	9,602
Other Georgraphic Area [Member]
Net sales to customers by geography are as follows:
Net Sales by product group		13,154	14,345	26,765	27,934
Net Sales by product group		$ 96,249	$ 96,277	$ 192,961	$ 198,717

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