14. STOCK-BASED COMPENSATION (Details 5) $ / shares in Units, $ in Thousands	9 Months Ended
	Feb. 28, 2021 USD ($) $ / shares shares
$1.22-$1.34
Options outstanding, ending (in thousands) | shares	133
Weighted average remaining contractual life (years) options outstanding	6 years 3 months 18 days
Weighted average exercise price outstanding, ending | $ / shares	$ 1.27
Options exercisable shares, ending (in thousands) | shares	36
Weighted average remaining contractual life (years) options exercisable	6 years 4 months 10 days
Weighted average exercise price for options exercisable, ending | $ / shares	$ 1.28
$1.64-$1.86
Options outstanding, ending (in thousands) | shares	1,047
Weighted average remaining contractual life (years) options outstanding	5 years 14 days
Weighted average exercise price outstanding, ending | $ / shares	$ 1.7
Options exercisable shares, ending (in thousands) | shares	589
Weighted average remaining contractual life (years) options exercisable	4 years 6 months
Weighted average exercise price for options exercisable, ending | $ / shares	$ 1.69
$2.03-$2.46
Options outstanding, ending (in thousands) | shares	1,017
Weighted average remaining contractual life (years) options outstanding	3 years 3 months
Weighted average exercise price outstanding, ending | $ / shares	$ 2.21
Options exercisable shares, ending (in thousands) | shares	781
Weighted average remaining contractual life (years) options exercisable	2 years 10 months 10 days
Weighted average exercise price for options exercisable, ending | $ / shares	$ 2.19
$2.63-$2.81
Options outstanding, ending (in thousands) | shares	405
Weighted average remaining contractual life (years) options outstanding	7 months 28 days
Weighted average exercise price outstanding, ending | $ / shares	$ 2.71
Options exercisable shares, ending (in thousands) | shares	404
Weighted average remaining contractual life (years) options exercisable	7 months 24 days
Weighted average exercise price for options exercisable, ending | $ / shares	$ 2.71
$3.46-$3.93
Options outstanding, ending (in thousands) | shares	202
Weighted average remaining contractual life (years) options outstanding	3 years 4 months 28 days
Weighted average exercise price outstanding, ending | $ / shares	$ 3.86
Options exercisable shares, ending (in thousands) | shares	184
Weighted average remaining contractual life (years) options exercisable	3 years 4 months 28 days
Weighted average exercise price for options exercisable, ending | $ / shares	$ 3.85
$1.22-$3.93
Options outstanding, ending (in thousands) | shares	2,804
Weighted average remaining contractual life (years) options outstanding	3 years 8 months 12 days
Weighted average exercise price outstanding, ending | $ / shares	$ 2.16
Options exercisable shares, ending (in thousands) | shares	1,994
Weighted average remaining contractual life (years) options exercisable	3 years 4 days
Weighted average exercise price for options exercisable, ending | $ / shares	$ 2.28
Aggregate intrinsic value for options exercisable | $	$ 1,224