FINANCIAL INSTRUMENTS (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Cash	$ 6,337
Adjusted Cost	77,897
Unrealized Gains(3)	247
Fair Value	78,144
Short-term Marketable Securities	61,678	$ 0
Cash and Cash Equivalents	16,466	$ 9,949
U.S. Treasury Securities, maturities less than three months
Schedule of Available-for-sale Securities [Line Items]
Fair Value	10,129
U.S. Treasury Securities, maturities greater than three months
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	61,431
Unrealized Gains(3)	247
Fair Value	$ 61,678