2. STOCK-BASED COMPENSATION - Compensation costs (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Feb. 28, 2015	Feb. 28, 2014	Feb. 28, 2015	Feb. 28, 2014
Stock-based compensation in the form of employee stock options and ESPP shares included in:
Total stock-based compensation	$ 219	$ 235	$ 693	$ 625
Cost of Sales
Stock-based compensation in the form of employee stock options and ESPP shares included in:
Total stock-based compensation	17	10	47	33
Selling, General and Administrative
Stock-based compensation in the form of employee stock options and ESPP shares included in:
Total stock-based compensation	148	184	508	471
Research and Development
Stock-based compensation in the form of employee stock options and ESPP shares included in:
Total stock-based compensation	$ 54	$ 41	$ 138	$ 121