11. STOCKHOLDERS' EQUITY, COMPREHENSIVE INCOME AND STOCK-BASED COMPENSATION (Details 5) $ / shares in Units, $ in Thousands	12 Months Ended
	May 31, 2020 USD ($) $ / shares shares
Option exercisable shares (in thousands) | shares	2,203
Weighted average exercise price for options exercisable | $ / shares	$ 2.25
$1.22-$1.28
Options outstanding, ending (in thousands) | shares	248
Weighted average remaining contractual life (Years) options outstanding	2 years 1 month 6 days
Weighted average exercise price outstanding, ending | $ / shares	$ 1.26
Option exercisable shares (in thousands) | shares	176
Weighted average remaining contractual life (Years) options exercisable	2 months 8 days
Weighted average exercise price for options exercisable | $ / shares	$ 1.28
$1.64-$1.77
Options outstanding, ending (in thousands) | shares	945
Weighted average remaining contractual life (Years) options outstanding	5 years 4 months 6 days
Weighted average exercise price outstanding, ending | $ / shares	$ 1.66
Option exercisable shares (in thousands) | shares	487
Weighted average remaining contractual life (Years) options exercisable	4 years 7 months 28 days
Weighted average exercise price for options exercisable | $ / shares	$ 1.68
$2.03-$2.46
Options outstanding, ending (in thousands) | shares	1,223
Weighted average remaining contractual life (Years) options outstanding	3 years 8 months 12 days
Weighted average exercise price outstanding, ending | $ / shares	$ 2.21
Option exercisable shares (in thousands) | shares	858
Weighted average remaining contractual life (Years) options exercisable	3 years 11 days
Weighted average exercise price for options exercisable | $ / shares	$ 2.19
$2.63-$2.81
Options outstanding, ending (in thousands) | shares	511
Weighted average remaining contractual life (Years) options outstanding	1 year 3 months 14 days
Weighted average exercise price outstanding, ending | $ / shares	$ 2.70
Option exercisable shares (in thousands) | shares	510
Weighted average remaining contractual life (Years) options exercisable	1 year 3 months 11 days
Weighted average exercise price for options exercisable | $ / shares	$ 2.70
$3.46-$3.93
Options outstanding, ending (in thousands) | shares	226
Weighted average remaining contractual life (Years) options outstanding	4 years 1 month 28 days
Weighted average exercise price outstanding, ending | $ / shares	$ 3.84
Option exercisable shares (in thousands) | shares	172
Weighted average remaining contractual life (Years) options exercisable	4 years 2 months 5 days
Weighted average exercise price for options exercisable | $ / shares	$ 3.82
$1.22-$3.93
Options outstanding, ending (in thousands) | shares	3,153
Weighted average remaining contractual life (Years) options outstanding	3 years 8 months 16 days
Weighted average exercise price outstanding, ending | $ / shares	$ 2.17
Option exercisable shares (in thousands) | shares	2,203
Weighted average remaining contractual life (Years) options exercisable	2 years 10 months 6 days
Weighted average exercise price for options exercisable | $ / shares	$ 2.25
Aggregate intrinsic value for options exercisable | $	$ 67