SHORT TERM INVESTMENTS, PREPAID EXPENSES AND OTHER CURRENT ASSETS - Schedule of Short Term Investments (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Short term investments	$ 15,673	$ 11,303
Government
Debt Securities, Available-for-sale [Line Items]
Short term investments	2,099	0
Asset Backed
Debt Securities, Available-for-sale [Line Items]
Short term investments	2,899	1,786
Industrial
Debt Securities, Available-for-sale [Line Items]
Short term investments	5,170	2,381
Financial
Debt Securities, Available-for-sale [Line Items]
Short term investments	$ 5,505	$ 7,136