CASH, CASH EQUIVALENTS AND SHORT-TERM INVESTMENTS - UNREALIZED LOSS POSITION (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)	Jun. 30, 2018 item
Cash, cash equivalents, short-term and marketable securities
Number of securities in an unrealized loss position | item		0
Corporate debt securities
Cash, cash equivalents, short-term and marketable securities
Fair Value, Less Than 12 Months	$ (1,205)
Gross Unrealized Losses, Less than 12 months	(5)
Fair Value, Total	1,205
Gross Unrealized Losses, Total	$ (5)