4. EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Feb. 28, 2019	Feb. 28, 2018	Feb. 28, 2019	Feb. 28, 2018
Earnings Per Share [Abstract]
Numerator: Net (loss) income	$ (3,201)	$ 267	$ (5,345)	$ 337
Denominator for basic net (loss) income per share: Weighted average shares outstanding (in thousands)	22,459	21,832	22,314	21,631
Shares used in basic net (loss) income per share calculation (in thousands)	22,459	21,832	22,314	21,631
Effect of dilutive securities (in thousands)	0	809	0	1,207
Denominator for diluted net (loss) income per share (in thousands)	22,459	22,641	22,314	22,838
Basic net (loss) income per share	$ (0.14)	$ 0.01	$ (0.24)	$ 0.02
Diluted net (loss) income per share	$ (0.14)	$ 0.01	$ (0.24)	$ 0.01