12. STOCKHOLDERS' EQUITY, COMPREHENSIVE INCOME AND STOCK-BASED COMPENSATION (Details Narrative) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Feb. 28, 2019	Feb. 28, 2018	Feb. 28, 2019	Feb. 28, 2018
Stock-based compensation costs capitalized as part of inventory	$ 0	$ 0	$ 0	$ 0
Intrinsic value of options exercised	160	214	$ 322	959
Weighted average remaining contractual life of the options exercisable and expected to be exercisable			3 years 8 months 12 days
Stock Option and RSU Transactions
Stock-based compensation expense related to stock options and RSUs	$ 166	$ 206	$ 505	$ 614
Restricted Stock Units granted (in thousands)	0	0	0	64
Market value on the date of the grant				$ 3.93
Restricted Stock Units vested (in thousands)	4	4	13	11
Restricted Stock Units unvested (in thousands)	34	85	34	85
Restricted Stock Units unvested intrinsic value	$ 50	$ 194	$ 50	$ 194
2016 Equity Incentive Plan
Unrecognized stock-based compensation	1,466		1,466
Estimated forfeitures of unvested stock based awards, amount	4		$ 4
Weighted average period for recognition of costs			3 years 1 month 6 days
Employee Stock Purchase Plan
Weighted average period for recognition of costs			1 year 2 months 12 days
Stock-based compensation related to the ESPP	59	$ 36	$ 200	$ 208
Compensation cost related to purchase rights under the ESPP but not yet recognized	$ 174		$ 174
ESPP purchase right granted (in thousands)	0	0	327	0
ESPP shares issued (in thousands)			64	116
ESPP shares available for issuance (in thousands)	430		430