Note 15 - Segment and Geographic Information (Details) - Net Export Sales to Unaffiliated Customers (USD $) In Thousands, unless otherwise specified	3 Months Ended				6 Months Ended
	Nov. 30, 2013		Nov. 30, 2012		Nov. 30, 2013		Nov. 30, 2012
Net sales to customers by geography are as follows:
Net sales to customers by geography	$ 100,203		$ 82,056		$ 196,247		$ 167,210
United States [Member]
Net sales to customers by geography are as follows:
Net sales to customers by geography	61,416		52,968		122,546		110,253
Europe [Member]
Net sales to customers by geography are as follows:
Net sales to customers by geography	19,373		15,170		37,289		30,039
Canada [Member]
Net sales to customers by geography are as follows:
Net sales to customers by geography	5,061	[1]	4,497	[1]	9,614	[1]	9,574	[1]
Other Geographic Area [Member]
Net sales to customers by geography are as follows:
Net sales to customers by geography	$ 14,353		$ 9,421		$ 26,798		$ 17,344

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