O. SEGMENT AND GEOGRAPHIC INFORMATION - NARRATIVE (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues	$ 79,855	$ 88,879	$ 117,371	$ 96,224	$ 84,900	$ 70,137	$ 55,254	$ 50,422	$ 382,329	$ 260,713	$ 189,903
Internet data center [Member] | Sales Revenue, Net [Member]
Revenues									$ 306,700	$ 201,300	$ 123,200
Concentration percentage									80.20%	77.20%	64.90%
CATV markets [Member] | Sales Revenue, Net [Member]
Revenues									$ 60,800	$ 43,600	$ 53,700
Concentration percentage									15.90%	16.70%	28.30%
FTTH markets [Member] | Sales Revenue, Net [Member]
Revenues									$ 500	$ 1,600	$ 2,500
Concentration percentage									0.10%	0.60%	1.30%
Telecom markets [Member] | Sales Revenue, Net [Member]
Revenues									$ 12,900	$ 12,900	$ 9,700
Concentration percentage									3.40%	5.00%	5.10%