S. SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 52,952	$ 57,085	$ 49,632	$ 30,234	$ 36,391	$ 36,549	$ 32,650	$ 24,859	$ 189,903	$ 130,449	$ 78,424
Cost of goods sold	37,334	39,032	32,901	20,183	24,132	24,403	21,462	16,206	129,450	86,203	55,396
Gross profit	$ 15,618	$ 18,053	$ 16,731	$ 10,051	$ 12,259	$ 12,146	$ 11,188	$ 8,653	60,453	44,246	23,028
Gross margin	29.50%	31.60%	33.70%	33.20%	33.70%	33.20%	34.30%	34.80%
Operating expenses:
Research and development	$ 5,960	$ 5,386	$ 4,701	$ 4,805	$ 4,221	$ 4,194	$ 4,009	$ 3,546	20,852	15,970	8,512
Sales and marketing	1,633	1,582	1,607	1,559	1,591	1,622	1,497	1,333	6,381	6,043	4,191
General and administrative	5,271	4,963	4,534	5,003	5,131	4,458	3,952	3,554	19,771	17,095	10,632
Total operating expenses	12,864	11,931	10,842	11,367	10,943	10,274	9,458	8,433	47,004	39,108	23,335
Income from operations	2,754	6,122	5,889	(1,316)	1,316	1,872	1,730	220	13,449	5,138	(307)
Interest and other income (expense), net	(241)	(3,016)	335	641	(602)	(218)	274	(110)	(1,591)	(699)	(78)
Net income before taxes	2,513	3,106	6,224	(675)	714	1,654	2,004	110
Income taxes	166	(406)	(135)	0	(12)	(77)	(85)	(25)	375	199	0
Net income	$ 2,679	$ 2,700	$ 6,089	$ (675)	$ 702	$ 1,577	$ 1,919	$ 85	$ 10,793	$ 4,283	$ (1,406)
Net income per share - basic	$ .16	$ .17	$ .41	$ (.05)	$ 0.05	$ 0.11	$ 0.13	$ 0.01	$ 0.69	$ 0.30	$ (.14)
Net income per share - diluted	$ .15	$ .16	$ .38	$ (.05)	$ 0.05	$ 0.10	$ 0.12	$ 0.01	$ .65	$ 0.28	$ (.14)