2. STOCK-BASED COMPENSATION - Compensation costs (Details) - USD ($) $ in Thousands	3 Months Ended
	Aug. 31, 2015	Aug. 31, 2014
Stock-based compensation in the form of employee stock options and ESPP shares included in:
Total stock-based compensation	$ 319	$ 197
Cost of Sales
Stock-based compensation in the form of employee stock options and ESPP shares included in:
Total stock-based compensation	22	14
Selling, General and Administrative
Stock-based compensation in the form of employee stock options and ESPP shares included in:
Total stock-based compensation	238	148
Research and Development
Stock-based compensation in the form of employee stock options and ESPP shares included in:
Total stock-based compensation	$ 59	$ 35