13. STOCK-BASED COMPENSATION (Details 4) $ / shares in Units, $ in Thousands	9 Months Ended
	Feb. 29, 2020 USD ($) $ / shares shares
$1.09-$1.28
Options outstanding, ending (in thousands) | shares	177
Weighted average remaining contractual life (years) options outstanding	3 months 29 days
Weighted average exercise price outstanding, ending | $ / shares	$ 1.28
Options exercisable shares, ending (in thousands) | shares	177
Weighted average remaining contractual life (years) options exercisable	3 months 29 days
Weighted average exercise price for options exercisable, ending | $ / shares	$ 1.28
$1.64-$2.06
Options outstanding, ending (in thousands) | shares	1,183
Weighted average remaining contractual life (years) options outstanding	5 years 3 months 18 days
Weighted average exercise price outstanding, ending | $ / shares	$ 1.76
Options exercisable shares, ending (in thousands) | shares	520
Weighted average remaining contractual life (years) options exercisable	4 years 3 months 11 days
Weighted average exercise price for options exercisable, ending | $ / shares	$ 1.8
$2.10-$2.81
Options outstanding, ending (in thousands) | shares	1,436
Weighted average remaining contractual life (years) options outstanding	2 years 10 months 24 days
Weighted average exercise price outstanding, ending | $ / shares	$ 2.43
Options exercisable shares, ending (in thousands) | shares	1,166
Weighted average remaining contractual life (years) options exercisable	2 years 3 months 22 days
Weighted average exercise price for options exercisable, ending | $ / shares	$ 2.43
$3.46-$3.93
Options outstanding, ending (in thousands) | shares	228
Weighted average remaining contractual life (years) options outstanding	4 years 44 months 28 days
Weighted average exercise price outstanding, ending | $ / shares	$ 3.85
Options exercisable shares, ending (in thousands) | shares	162
Weighted average remaining contractual life (years) options exercisable	4 years 5 months 8 days
Weighted average exercise price for options exercisable, ending | $ / shares	$ 3.81
$1.09-$3.93
Options outstanding, ending (in thousands) | shares	3,024
Weighted average remaining contractual life (years) options outstanding	3 years 9 months 18 days
Weighted average exercise price outstanding, ending | $ / shares	$ 2.21
Options exercisable shares, ending (in thousands) | shares	2,025
Weighted average remaining contractual life (years) options exercisable	2 years 9 months 22 days
Weighted average exercise price for options exercisable, ending | $ / shares	$ 2.28
Aggregate intrinsic value for options exercisable | $	$ 301