5. ACCOUNTS RECEIVABLE (Details) - USD ($) $ in Thousands		12 Months Ended
		May 31, 2020	May 31, 2019	May 31, 2020	May 31, 2019
Receivables [Abstract]
Accounts receivable, gross				$ 3,717	$ 4,859
Less: Allowance for doubtful accounts		$ 0	$ 4	0	0
Accounts receivable, net				$ 3,717	$ 4,859
Allowance for doubtful accounts, beginning		0	4
Allowance for doubtful accounts, additions charged to costs and expenses		0	0
Allowance for doubtful accounts, deductions	[1]	(0)	(4)
Allowance for doubtful accounts, ending		$ 0	$ 0

[1] Deductions include write-offs of uncollectible accounts, collections of amounts previously reserved, and releases of allowance for doubtful accounts credited to expense.