QUARTERLY RESULTS (UNAUDITED) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net revenues	$ 116,306	$ 93,461	$ 98,701	$ 103,319	$ 112,684	$ 104,046	$ 98,615	$ 97,937	$ 411,788	$ 413,282	$ 419,003
Cost of Revenue	43,033	35,603	40,253	40,087	44,220	41,485	40,333	40,280	162,713	174,118	176,887
Cost, Amortization										7,800	7,800
Cost of services										55,560	56,481
Gross profit	73,273	57,858	56,660	61,282	66,514	60,611	56,332	55,707	249,075	239,164	242,116
Operating expenses:
Research and development	16,018	14,860	15,180	16,285	14,836	15,873	15,985	15,685	62,343	62,379	68,212
Marketing and selling	26,603	22,334	26,129	24,878	23,921	23,461	27,759	26,132	99,944	101,273	106,257
General and administrative	14,816	12,034	12,722	13,788	13,574	13,660	14,041	13,955	53,362	55,230	53,892
Amortization of intangible assets	0	0	331	363	361	363	363	363	694	1,450	1,450
Restructuring costs (recoveries), net	113	229	(269)	558	1,747	226	268	2,907	629	5,148	7,059
Total operating expenses	57,550	49,457	54,093	55,872	54,439	53,583	58,416	59,042	216,972	225,480	236,870
Operating income (loss)	15,723	8,401	2,567	5,410	12,075	7,028	(2,084)	(3,335)	32,103	13,684	5,246
Other income (expense), net	(5,584)	(5,519)	(13,290)	(5,185)	(5,725)	(5,725)	(6,278)	(5,359)	(2,902)	192	761
Income (loss) before income taxes	10,139	2,882	(10,723)	225	6,350	1,303	(8,362)	(8,694)	2,525	(9,403)	(13,422)
Provision for (benefit from) income taxes	(5,231)	(283)	0	438	447	425	144	255	(5,076)	1,271	133
Net income (loss)	$ 15,370	$ 3,165	$ (10,723)	$ (213)	$ 5,903	$ 878	$ (8,506)	$ (8,949)	$ 7,601	$ (10,674)	$ (13,555)
Earnings Per Share, Basic	$ 0.36	$ 0.07	$ (0.25)	$ (0.01)	$ 0.14	$ 0.02	$ (0.20)	$ (0.22)	$ 0.18	$ (0.26)	$ (0.33)
Earnings Per Share, Diluted	$ 0.35	$ 0.07	$ (0.25)	$ (0.01)	$ 0.14	$ 0.02	$ (0.20)	$ (0.22)	$ 0.17	$ (0.26)	$ (0.33)
Weighted-average common shares outstanding - basic	43,060	42,913	42,560	42,046	41,860	41,792	41,587	41,404	42,649	41,662	41,020
Weighted-average common shares outstanding - diluted	43,737	43,674	42,560	42,046	42,430	42,226	41,587	41,404	43,495	41,662	41,020
Amortization of intangible assets [Member]
Cost, Amortization	$ 0	$ 0	$ 1,788	$ 1,950	$ 1,950	$ 1,950	$ 1,950	$ 1,950	$ 3,738
Convertible Debt [Member]
Interest Expense, Debt									$ 4,400	$ 8,800