QUARTERLY RESULTS (UNAUDITED) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Net revenues	$ 104,301	$ 90,431	$ 79,281	$ 86,453	$ 116,306	$ 93,461	$ 98,701	$ 103,319	$ 360,466	$ 411,788	$ 413,282
Amortization of intangible assets									0	3,738	7,800
Cost of services	38,951	32,174	27,719	33,302	43,033	35,603	40,253	40,087
Gross profit	65,350	58,257	51,562	53,151	73,273	57,858	56,660	61,282	228,320	249,075	239,164
Operating expenses:
Research and development	14,902	13,623	13,068	15,425	16,018	14,860	15,180	16,285	57,018	62,343	62,379
Marketing and selling	22,660	19,998	19,690	25,289	26,603	22,334	26,129	24,878	87,637	99,944	101,273
General and administrative	12,908	10,796	10,604	12,744	14,816	12,034	12,722	13,788	47,052	53,362	55,230
Amortization of intangible assets	0	0	0	0	0	0	331	363	0	694	1,450
Restructuring costs (recoveries), net	4,038	723	140	145	113	229	(269)	558	5,046	629	5,148
Total operating expenses	54,508	45,140	43,502	53,603	57,550	49,457	54,093	55,872	196,753	216,972	225,480
Operating income (loss)	10,842	13,117	8,060	(452)	15,723	8,401	2,567	5,410	31,567	32,103	13,684
Other income (expense), net	(3,929)	(4,423)	(5,498)	(5,283)	(5,584)	(5,519)	(13,290)	(5,185)
Income (loss) before income taxes	6,913	8,694	2,562	(5,735)	10,139	2,882	(10,723)	225	12,434	2,525	(9,403)
Provision for (benefit from) income taxes	(174)	707	717	122	(5,231)	(283)	0	438	1,372	(5,076)	1,271
Net income (loss)	$ 7,087	$ 7,987	$ 1,845	$ (5,857)	$ 15,370	$ 3,165	$ (10,723)	$ (213)	$ 11,062	$ 7,601	$ (10,674)
Earnings Per Share, Basic	$ 0.16	$ 0.18	$ 0.04	$ (0.14)	$ 0.36	$ 0.07	$ (0.25)	$ (0.01)	$ 0.25	$ 0.18	$ (0.26)
Earnings Per Share, Diluted	$ 0.16	$ 0.18	$ 0.04	$ (0.13)	$ 0.35	$ 0.07	$ (0.25)	$ (0.01)	$ 0.25	$ 0.17	$ (0.26)
Weighted-average common shares outstanding - basic	44,288	44,019	43,719	43,254	43,060	42,913	42,560	42,046	43,822	42,649	41,662
Weighted-average common shares outstanding - diluted	45,541	44,758	44,180	44,101	43,737	43,674	42,560	42,046	44,878	43,495	41,662
Amortization of intangible assets [Member]
Amortization of intangible assets	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 1,788	$ 1,950
Convertible Debt [Member]
Interest Expense, Debt									$ 900	$ 4,400