4. CASH, CASH EQUIVALENTS AND INVESTMENTS (Details) - USD ($) $ in Thousands	Nov. 30, 2017	May 31, 2017	[1]	Nov. 30, 2016	May 31, 2016
Cash, cost	$ 1,802
Cash, estimated fair value	1,802
Cash equivalents, cost	8,157
Cash equivalents, estimated fair value	8,157
Cash and cash equivalents, cost	9,959	$ 17,803		$ 5,154	$ 939
Cash and cash equivalents, estimated fair value	9,959	$ 17,803		$ 5,154	$ 939
Short-term investments, gross unrealized loss	3
Cash, cash equivalents, and investments, cost	15,931
Cash, cash equivalents, and investments, gross unrealized loss	3
Cash, cash equivalents, and investments, estimated fair value	15,928
Money Market Funds At Carrying Value
Cash equivalents, cost	4,164
Cash equivalents, estimated fair value	4,164
U.S. Treasury securities
Cash equivalents, cost	3,993
Cash equivalents, estimated fair value	3,993
Short-term investments, cost	5,972
Short-term investments, gross unrealized loss	3
Short-term investments, estimated fair value	5,969
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.