CONCENTRATION OF RISK - Revenues by Geographic Area (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Concentration Risk [Line Items]
Revenues	$ 77,550	$ 61,683	$ 177,271	$ 219,762
South Korea [Member]
Concentration Risk [Line Items]
Revenues	53,883	45,803	126,789	185,937
China [Member]
Concentration Risk [Line Items]
Revenues	17,037	10,234	34,368	18,130
Japan [Member]
Concentration Risk [Line Items]
Revenues	3,076	2,462	4,637	5,590
Other Non-U.S. Locations [Member]
Concentration Risk [Line Items]
Revenues	457	597	2,078	2,132
Total Non-U.S. Locations [Member]
Concentration Risk [Line Items]
Revenues	74,453	59,096	167,872	211,789
UNITED STATES
Concentration Risk [Line Items]
Revenues	$ 3,097	$ 2,587	$ 9,399	$ 7,973