CONCENTRATION OF RISK - Revenues by Geographic Area (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Concentration Risk [Line Items]
Revenues	$ 97,515	$ 77,550	$ 303,448	$ 177,271
South Korea [Member]
Concentration Risk [Line Items]
Revenues	70,042	53,883	190,303	126,789
China [Member]
Concentration Risk [Line Items]
Revenues	23,205	17,037	98,955	34,368
Japan [Member]
Concentration Risk [Line Items]
Revenues	1,137	3,076	3,802	4,637
Other Non-U.S. Locations [Member]
Concentration Risk [Line Items]
Revenues	539	457	1,718	2,078
Total Non-U.S. Locations [Member]
Concentration Risk [Line Items]
Revenues	94,923	74,453	294,778	167,872
United States [Member]
Concentration Risk [Line Items]
Revenues	$ 2,592	$ 3,097	$ 8,670	$ 9,399