12. STOCKHOLDERS' EQUITY, COMPREHENSIVE INCOME AND STOCK-BASED COMPENSATION (Details 1) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Feb. 28, 2019	Feb. 28, 2018	Feb. 28, 2019	Feb. 28, 2018
Stock-based compensation in the form of employee stock options, RSUs and ESPP purchase rights, included in:
Total stock-based compensation	$ 225	$ 242	$ 705	$ 822
Cost of Sales
Stock-based compensation in the form of employee stock options, RSUs and ESPP purchase rights, included in:
Total stock-based compensation	24	28	83	107
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	137	162	421	530
Research and Development
Stock-based compensation in the form of employee stock options, RSUs and ESPP purchase rights, included in:
Total stock-based compensation	$ 64	$ 52	$ 201	$ 185