14. STOCK-BASED COMPENSATION (Details 4) $ / shares in Units, $ in Thousands	3 Months Ended
	Aug. 31, 2020 USD ($) $ / shares shares
$1.22
Options outstanding, ending (in thousands) | shares	75
Weighted average remaining contractual life (years) options outstanding	6 years 6 months 14 days
Weighted average exercise price outstanding, ending | $ / shares	$ 1.22
Options exercisable shares, ending (in thousands) | shares	8
Weighted average remaining contractual life (years) options exercisable	6 years 6 months 14 days
Weighted average exercise price for options exercisable, ending | $ / shares	$ 1.22
$1.64-$1.86
Options outstanding, ending (in thousands) | shares	1,105
Weighted average remaining contractual life (years) options outstanding	5 years 5 months 19 days
Weighted average exercise price outstanding, ending | $ / shares	$ 1.70
Options exercisable shares, ending (in thousands) | shares	546
Weighted average remaining contractual life (years) options exercisable	4 years 8 months 19 days
Weighted average exercise price for options exercisable, ending | $ / shares	$ 1.68
$2.03-$2.46
Options outstanding, ending (in thousands) | shares	1,162
Weighted average remaining contractual life (years) options outstanding	3 years 5 months 26 days
Weighted average exercise price outstanding, ending | $ / shares	$ 2.21
Options exercisable shares, ending (in thousands) | shares	846
Weighted average remaining contractual life (years) options exercisable	2 years 11 months 1 day
Weighted average exercise price for options exercisable, ending | $ / shares	$ 2.19
$2.63-$2.81
Options outstanding, ending (in thousands) | shares	464
Weighted average remaining contractual life (years) options outstanding	1 year 14 days
Weighted average exercise price outstanding, ending | $ / shares	$ 2.70
Options exercisable shares, ending (in thousands) | shares	462
Weighted average remaining contractual life (years) options exercisable	1 year 11 days
Weighted average exercise price for options exercisable, ending | $ / shares	$ 2.70
$3.46-$3.93
Options outstanding, ending (in thousands) | shares	211
Weighted average remaining contractual life (years) options outstanding	3 years 10 months 24 days
Weighted average exercise price outstanding, ending | $ / shares	$ 3.86
Options exercisable shares, ending (in thousands) | shares	171
Weighted average remaining contractual life (years) options exercisable	3 years 10 months 28 days
Weighted average exercise price for options exercisable, ending | $ / shares	$ 3.85
$1.22-$3.93
Options outstanding, ending (in thousands) | shares	3,017
Weighted average remaining contractual life (years) options outstanding	3 years 11 months 8 days
Weighted average exercise price outstanding, ending | $ / shares	$ 2.19
Options exercisable shares, ending (in thousands) | shares	2,033
Weighted average remaining contractual life (years) options exercisable	3 years 25 days
Weighted average exercise price for options exercisable, ending | $ / shares	$ 2.31
Aggregate intrinsic value for options exercisable | $	$ 59