M. SHARE-BASED COMPENSATION - SHARE-BASED COMPENSATION EXPENSE (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Total share-based compensation expense	$ 7,795	$ 3,833	$ 2,120
Employee Stock Option
Total share-based compensation expense	853	1,460	1,538
Restricted stock units
Total share-based compensation expense	6,942	2,373	582
Cost of sales [Member]
Total share-based compensation expense	461	190	70
Research and development [Member]
Total share-based compensation expense	1,496	591	230
Sales and marketing [Member]
Total share-based compensation expense	481	357	217
General and administrative [Member]
Total share-based compensation expense	$ 5,357	$ 2,695	$ 1,603