12. STOCKHOLDERS' EQUITY, COMPREHENSIVE INCOME AND STOCK-BASED COMPENSATION (Details 5) $ / shares in Units, $ in Thousands	9 Months Ended
	Feb. 28, 2019 USD ($) $ / shares shares
$0.80-$0.97
Options outstanding, ending (in thousands) | shares	47
Weighted average remaining contractual life (years) options outstanding	9 months 7 days
Weighted average exercise price outstanding, ending | $ / shares	$ .85
Options exercisable shares, ending (in thousands) | shares	47
Weighted average remaining contractual life (years) options exercisable	9 months 7 days
Weighted average exercise price for options exercisable, ending | $ / shares	$ .85
$1.09-$1.28
Options outstanding, ending (in thousands) | shares	498
Weighted average remaining contractual life (years) options outstanding	11 months 19 days
Weighted average exercise price outstanding, ending | $ / shares	$ 1.28
Options exercisable shares, ending (in thousands) | shares	498
Weighted average remaining contractual life (years) options exercisable	11 months 19 days
Weighted average exercise price for options exercisable, ending | $ / shares	$ 1.28
$1.68-$2.06
Options outstanding, ending (in thousands) | shares	763
Weighted average remaining contractual life (years) options outstanding	4 years 9 months 4 days
Weighted average exercise price outstanding, ending | $ / shares	$ 1.83
Options exercisable shares, ending (in thousands) | shares	386
Weighted average remaining contractual life (years) options exercisable	3 years 6 months 14 days
Weighted average exercise price for options exercisable, ending | $ / shares	$ 1.79
$2.10-$2.81
Options outstanding, ending (in thousands) | shares	1,651
Weighted average remaining contractual life (years) options outstanding	3 years 10 months 17 days
Weighted average exercise price outstanding, ending | $ / shares	$ 2.43
Options exercisable shares, ending (in thousands) | shares	1,199
Weighted average remaining contractual life (years) options exercisable	2 years 11 months 23 days
Weighted average exercise price for options exercisable, ending | $ / shares	$ 2.44
$3.46-$3.93
Options outstanding, ending (in thousands) | shares	261
Weighted average remaining contractual life (years) options outstanding	5 years 4 months 28 days
Weighted average exercise price outstanding, ending | $ / shares	$ 3.86
Options exercisable shares, ending (in thousands) | shares	128
Weighted average remaining contractual life (years) options exercisable	5 years 5 months 12 days
Weighted average exercise price for options exercisable, ending | $ / shares	$ 3.78
$0.80-$3.93
Options outstanding, ending (in thousands) | shares	3,220
Weighted average remaining contractual life (years) options outstanding	3 years 8 months 19 days
Weighted average exercise price outstanding, ending | $ / shares	$ 2.20
Options exercisable shares, ending (in thousands) | shares	2,258
Weighted average remaining contractual life (years) options exercisable	2 years 8 months 23 days
Weighted average exercise price for options exercisable, ending | $ / shares	$ 2.11
Aggregate intrinsic value for options exercisable, ending | $	$ 120