QUARTERLY RESULTS (UNAUDITED) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Net revenues	$ 112,684	$ 104,046	$ 98,615	$ 97,937	$ 107,258	$ 105,265	$ 102,373	$ 104,107	$ 413,282	$ 419,003	$ 511,930
Cost of revenues	44,220	41,485	40,333	40,280	46,862	42,957	40,670	38,598
Cost of products									110,758	112,606	111,579
Cost of services									55,560	56,481	59,828
Amortization of intangible assets	1,950	1,950	1,950	1,950	1,950	1,950	1,950	1,950	7,800	7,800	7,800
Gross profit	66,514	60,611	56,332	55,707	58,446	60,358	59,753	63,559	239,164	242,116	332,723
Operating expenses:
Research and development	14,836	15,873	15,985	15,685	16,308	16,025	16,991	18,888	62,379	68,212	81,564
Marketing and selling	23,921	23,461	27,759	26,132	25,776	25,652	29,018	25,811	101,273	106,257	110,338
General and administrative	13,574	13,660	14,041	13,955	10,624	15,193	13,644	14,431	55,230	53,892	61,471
Amortization of intangible assets	361	363	363	363	362	362	363	363	1,450	1,450	2,498
Restructuring costs (recoveries), net	1,747	226	268	2,907	595	(582)	6,063	983	5,148	7,059	12,837
Total operating expenses	54,439	53,583	58,416	59,042	53,665	56,650	66,079	60,476	225,480	236,870	268,708
Operating income (loss)	12,075	7,028	(2,084)	(3,335)	4,781	3,708	(6,326)	3,083	13,684	5,246	64,015
Other income (expense), net	(5,725)	(5,725)	(6,278)	(5,359)	(5,203)	(4,701)	(3,918)	(4,846)	192	761	232
Income (loss) before income taxes	6,350	1,303	(8,362)	(8,694)	(422)	(993)	(10,244)	(1,763)	(9,403)	(13,422)	45,344
Provision for (benefit from) income taxes	447	425	144	255	459	(1,065)	587	152	1,271	133	(2,875)
Net income (loss)	$ 5,903	$ 878	$ (8,506)	$ (8,949)	$ (881)	$ 72	$ (10,831)	$ (1,915)	$ (10,674)	$ (13,555)	$ 48,219
Net income (loss) per common share - basic and diluted	$ 0.14	$ 0.02	$ (0.20)	$ (0.22)	$ (0.02)	$ 0.00	$ (0.26)	$ (0.05)	$ (0.0026)
Weighted-average common shares outstanding - basic	41,860	41,792	41,587	41,404	41,216	41,133	40,953	40,772	41,662	41,020	40,021
Weighted-average common shares outstanding - diluted	42,430	42,226	41,587	41,404	41,216	41,355	40,953	40,772	41,662	41,020	40,176