3. CASH, CASH EQUIVALENTS AND INVESTMENTS (Details) - USD ($) $ in Thousands	Aug. 31, 2018	May 31, 2018		Aug. 31, 2017	May 31, 2017
Cash, cost	$ 2,587	$ 3,132
Cash, estimated fair value	2,587	3,132
Cash equivalents, cost	13,277	13,716
Cash equivalents, estimated fair value	13,277	13,716
Cash and cash equivalents, cost	15,864	16,848	[1]	$ 13,993	$ 17,803
Cash and cash equivalents, estimated fair value	15,864	16,848
Long-term investments, certificate of deposit, cost	80	80
Long-term investments, certificate of deposit, estimed fair value	80	80
Cash, cash equivalents, and investments, cost	15,944	16,928
Cash, cash equivalents, and investments, estimated fair value	15,944	16,928
Money Market Funds At Carrying Value
Cash equivalents, cost	13,277	7,733
Cash equivalents, estimated fair value	13,277	7,733
U.S. Treasury securities
Cash equivalents, cost	0	5,983
Cash equivalents, estimated fair value	$ 0	$ 5,983

[1] The condensed consolidated balance sheet at May 31, 2018 has been derived from the audited consolidated financial statements at that date.