Note 15 - Segment and Geographic Information (Details) - Net Export Sales to Unaffiliated Customers (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Aug. 31, 2013		Aug. 31, 2012
Net sales to customers by geography are as follows:
Net Sales to Customers	$ 96,044		$ 85,154
United States [Member]
Net sales to customers by geography are as follows:
Net Sales to Customers	61,120		57,825
Europe [Member]
Net sales to customers by geography are as follows:
Net Sales to Customers	17,851	[1]	14,869	[1]
Canada [Member]
Net sales to customers by geography are as follows:
Net Sales to Customers	4,553		5,078
Other Geographic Area [Member]
Net sales to customers by geography are as follows:
Net Sales to Customers	$ 12,520		$ 7,382

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