QUARTERLY RESULTS (UNAUDITED) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ 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
Net revenues	$ 107,258	$ 105,265	$ 102,373	$ 104,107	$ 115,295	$ 119,019	$ 134,069	$ 143,547	$ 419,003	$ 511,930	$ 505,595
Cost of revenues	46,862	42,957	40,670	38,598	43,876	41,678	44,320	41,533
Cost of products									112,606	111,579	131,881
Cost of services									56,481	59,828	61,501
Amortization of intangible assets	1,950	1,950	1,950	1,950	1,950	1,950	1,950	1,950	7,800	7,800	4,063
Gross profit	58,446	60,358	59,753	63,559	69,469	75,391	87,799	100,064	242,116	332,723	308,150
Operating expenses:
Research and development	16,308	16,025	16,991	18,888	18,773	19,953	21,433	21,405	68,212	81,564	95,898
Marketing and selling	25,776	25,652	29,018	25,811	21,311	27,231	30,177	31,619	106,257	110,338	122,511
General and administrative	10,624	15,193	13,644	14,431	13,112	13,822	16,818	17,719	53,892	61,471	74,109
Amortization of intangible assets	362	362	363	363	363	567	782	786	1,450	2,498	2,354
Restructuring costs (recoveries), net	595	(582)	6,063	983	4,959	5,314	(213)	2,777	7,059	12,837	6,305
Total operating expenses	53,665	56,650	66,079	60,476	58,518	66,887	68,997	74,306	236,870	268,708	301,177
Operating income (loss)	4,781	3,708	(6,326)	3,083	10,951	8,504	18,802	25,758	5,246	64,015	6,973
Other income (expense), net	(5,203)	(4,701)	(3,918)	(4,846)	(4,622)	(4,707)	(5,159)	(4,183)	761	232	(175)
Income (loss) before income taxes	(422)	(993)	(10,244)	(1,763)	6,329	3,797	13,643	21,575	(13,422)	45,344	565
Provision for (benefit from) income taxes	459	(1,065)	587	152	1,108	(5,321)	703	635	133	(2,875)	(1,915)
Net income (loss)	$ (881)	$ 72	$ (10,831)	$ (1,915)	$ 5,221	$ 9,118	$ 12,940	$ 20,940	$ (13,555)	$ 48,219	$ 2,480
Net income (loss) per common share - basic and diluted	$ (0.02)	$ 0.00	$ (0.26)	$ (0.05)	$ 0.13	$ 0.23	$ 0.33	$ 0.53
Weighted-average common shares outstanding - basic	41,216	41,133	40,953	40,772	40,637	40,194	39,678	39,566	41,020	40,021	39,423
Weighted-average common shares outstanding - diluted	41,216	41,355	40,953	40,772	40,746	40,476	39,734	39,640	41,020	40,176	40,380