CASH EQUIVALENTS AND SHORT-TERM INVESTMENTS (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Cash equivalents total	$ 54,093	$ 82,152	$ 297,082	$ 145,373
Demand Deposits [Member]
Cash equivalents total	11,300	56,200
Money market funds [Member]
Cash equivalents total	$ 42,795	$ 25,968