STOCK-BASED COMPENSATION (Details 4) $ / shares in Units, $ in Thousands	6 Months Ended
	Nov. 30, 2021 USD ($) $ / shares shares
$1.22-$1.34
Options outstanding, ending (in thousands) | shares	97,000
Weighted average remaining contractual life (Years) options outstanding	5 years 7 months 6 days
Weighted average exercise price outstanding, ending | $ / shares	$ 1.28
Option exercisable shares (in thousands) | shares	54,000
Weighted average remaining contractual life (Years) options exercisable	5 years 10 months 9 days
Weighted average exercise price for options exercisable | $ / shares	$ 1.33
$1.64-$1.86
Options outstanding, ending (in thousands) | shares	682,000
Weighted average remaining contractual life (Years) options outstanding	4 years 6 months 3 days
Weighted average exercise price outstanding, ending | $ / shares	$ 1.71
Option exercisable shares (in thousands) | shares	356,000
Weighted average remaining contractual life (Years) options exercisable	4 years 18 days
Weighted average exercise price for options exercisable | $ / shares	$ 1.69
$2.03-$2.46
Options outstanding, ending (in thousands) | shares	594,000
Weighted average remaining contractual life (Years) options outstanding	3 years 2 months 4 days
Weighted average exercise price outstanding, ending | $ / shares	$ 2.23
Option exercisable shares (in thousands) | shares	453,000
Weighted average remaining contractual life (Years) options exercisable	2 years 10 months 13 days
Weighted average exercise price for options exercisable | $ / shares	$ 2.22
$2.63-$2.93
Options outstanding, ending (in thousands) | shares	226,000
Weighted average remaining contractual life (Years) options outstanding	6 years 1 month 13 days
Weighted average exercise price outstanding, ending | $ / shares	$ 2.92
Option exercisable shares (in thousands) | shares	38,000
Weighted average remaining contractual life (Years) options exercisable	3 years 8 months 1 day
Weighted average exercise price for options exercisable | $ / shares	$ 2.84
$3.46-$3.93
Options outstanding, ending (in thousands) | shares	104,000
Weighted average remaining contractual life (Years) options outstanding	2 years 8 months 1 day
Weighted average exercise price outstanding, ending | $ / shares	$ 3.84
Option exercisable shares (in thousands) | shares	104,000
Weighted average remaining contractual life (Years) options exercisable	2 years 8 months 1 day
Weighted average exercise price for options exercisable | $ / shares	$ 3.84
$9.94-$19.85
Options outstanding, ending (in thousands) | shares	10,000
Weighted average remaining contractual life (Years) options outstanding	6 years 10 months 20 days
Weighted average exercise price outstanding, ending | $ / shares	$ 19.85
Option exercisable shares (in thousands) | shares	0
Weighted average remaining contractual life (Years) options exercisable	6 years 10 months 20 days
Weighted average exercise price for options exercisable | $ / shares	$ 19.85
$1.22-$19.85
Options outstanding, ending (in thousands) | shares	1,713,000
Weighted average remaining contractual life (Years) options outstanding	4 years 2 months 23 days
Weighted average exercise price outstanding, ending | $ / shares	$ 2.26
Option exercisable shares (in thousands) | shares	1,005,000
Weighted average remaining contractual life (Years) options exercisable	3 years 5 months 15 days
Weighted average exercise price for options exercisable | $ / shares	$ 2.18
Aggregate intrinsic value for options exercisable | $	$ 15,314