5. FAIR VALUE OF FINANCIAL INSTRUMENTS (Details) - USD ($) $ in Thousands	Nov. 30, 2019	May 31, 2019
Assets
Investment securities	$ 1,838	$ 3,017
Level 1
Assets
Investment securities	1,838	3,017
Level 2
Assets
Investment securities	0	0
Level 3
Assets
Investment securities	0	0
Money Market Funds
Assets
Investment securities	1,838	3,017
Money Market Funds | Level 1
Assets
Investment securities	1,838	3,017
Money Market Funds | Level 2
Assets
Investment securities	0	0
Money Market Funds | Level 3
Assets
Investment securities	$ 0	$ 0