12. STOCK-BASED COMPENSATION (Details) - USD ($) $ in Thousands	3 Months Ended
	Aug. 31, 2019	Aug. 31, 2018
Stock-based compensation in the form of employee stock options, RSUs and ESPP purchase rights, included in:
Total stock-based compensation	$ 199	$ 256
Cost of Sales
Stock-based compensation in the form of employee stock options, RSUs and ESPP purchase rights, included in:
Total stock-based compensation	19	36
Selling, General and Administrative
Stock-based compensation in the form of employee stock options, RSUs and ESPP purchase rights, included in:
Total stock-based compensation	130	148
Research and Development
Stock-based compensation in the form of employee stock options, RSUs and ESPP purchase rights, included in:
Total stock-based compensation	$ 50	$ 72