Basis of Presentation (Details Textual) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Nov. 30, 2012	Nov. 30, 2011	Nov. 30, 2012	Nov. 30, 2011	May 31, 2012
Basis of Presentation (Additional Textual) [Abstract]
Assets, liabilities, revenues and expenses of foreign subsidiaries			less than 10% of consolidated amounts
Demonstration equipment	$ 5,384		$ 5,384		$ 5,495
Shipping and handling cost	984	1,102	1,955	2,172
Reduction in selling, general and administrative expenses		$ 2,780		$ 5,553
Maximum [Member]
Basis of Presentation (Textual) [Abstract]
Operating lease agreements Period			3 years
Finance lease agreements Period			3 years
Period for demonstration equipment included in other assets			2 years
Minimum [Member]
Basis of Presentation (Textual) [Abstract]
Operating lease agreements Period	1 year
Finance lease agreements Period	1 year