CONCENTRATION OF RISK - Revenues by Geographic Area (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Concentration Risk [Line Items]
Revenues	$ 56,149	$ 102,513	$ 99,721	$ 158,079
South Korea [Member]
Concentration Risk [Line Items]
Revenues	42,132	92,206	72,906	140,134
China [Member]
Concentration Risk [Line Items]
Revenues	8,479	5,414	17,331	7,896
Japan [Member]
Concentration Risk [Line Items]
Revenues	686	2,044	1,561	3,128
Other Non-U.S. Locations [Member]
Concentration Risk [Line Items]
Revenues	1,061	822	1,622	1,534
Total Non-U.S. Locations [Member]
Concentration Risk [Line Items]
Revenues	52,358	100,486	93,420	152,692
UNITED STATES
Concentration Risk [Line Items]
Revenues	$ 3,791	$ 2,027	$ 6,301	$ 5,387