CONCENTRATION OF RISK - Revenues by Geographic Area (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Concentration Risk [Line Items]
Revenues	$ 118,168	$ 56,149	$ 205,933	$ 99,721
South Korea [Member]
Concentration Risk [Line Items]
Revenues	58,762	42,132	120,261	72,906
China [Member]
Concentration Risk [Line Items]
Revenues	54,972	8,479	75,750	17,331
Japan [Member]
Concentration Risk [Line Items]
Revenues	818	686	2,665	1,561
Other Non-U.S. Locations [Member]
Concentration Risk [Line Items]
Revenues	597	1,061	1,179	1,622
Total Non-U.S. Locations [Member]
Concentration Risk [Line Items]
Revenues	115,149	52,358	199,855	93,420
United States [Member]
Concentration Risk [Line Items]
Revenues	$ 3,019	$ 3,791	$ 6,078	$ 6,301