2. STOCK-BASED COMPENSATION - Compensation costs (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Feb. 28, 2014	Feb. 28, 2013	Feb. 28, 2014	Feb. 28, 2013
Stock-based compensation in the form of employee stock options and ESPP shares included in:
Total stock-based compensation	$ 235	$ 201	$ 625	$ 427
Cost of Sales
Stock-based compensation in the form of employee stock options and ESPP shares included in:
Total stock-based compensation	10	9	33	26
Selling, General and Administrative
Stock-based compensation in the form of employee stock options and ESPP shares included in:
Total stock-based compensation	184	159	471	315
Research and Development
Stock-based compensation in the form of employee stock options and ESPP shares included in:
Total stock-based compensation	$ 41	$ 33	$ 121	$ 86