4. CASH, CASH EQUIVALENTS AND INVESTMENTS (Details) - USD ($) $ in Thousands	Feb. 28, 2018	May 31, 2017	[1]	Feb. 28, 2017	May 31, 2016
Cash, cost	$ 1,899
Cash, estimated fair value	1,899
Cash equivalents, cost	7,178
Cash equivalents, estimated fair value	7,178
Cash and cash equivalents, cost	9,077	$ 17,803		$ 2,039	$ 939
Cash and cash equivalents, estimated fair value	9,077	$ 17,803		$ 2,039	$ 939
Long-term investments, certificate of deposit, cost	80
Long-term investments, certificate of deposit, estimed fair value	80
Cash, cash equivalents, and investments, cost	15,146
Cash, cash equivalents, and investments, estimated fair value	15,143
Money Market Funds At Carrying Value
Cash equivalents, cost	7,178
Cash equivalents, estimated fair value	7,178
U.S. Treasury securities
Cash equivalents, cost	0
Cash equivalents, estimated fair value	0
Short-term investments, cost	5,989
Short-term investments, gross unrealized loss	3
Short-term investments, estimated fair value	5,986
Cash, cash equivalents, and investments, gross unrealized loss	$ 3

[1] The condensed consolidated balance sheet at May 31, 2017 has been derived from the audited consolidated financial statements at that date.