CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Net revenues:
Products	$ 360,466	$ 411,788	$ 413,282
Cost of revenues:
Amortization of intangible assets	0	3,738	7,800
Total cost of revenues	132,146	162,713	174,118
Gross profit	228,320	249,075	239,164
Operating expenses:
Research and development	57,018	62,343	62,379
Marketing and selling	87,637	99,944	101,273
General and administrative	47,052	53,362	55,230
Amortization of intangible assets	0	694	1,450
Restructuring costs, net	5,046	629	5,148
Total operating expenses	196,753	216,972	225,480
Operating income	31,567	32,103	13,684
Interest income	70	36	195
Interest expense	(20,071)	(26,712)	(23,474)
Other income (expense), net	868	(2,902)	192
(Loss) income before income taxes	12,434	2,525	(9,403)
Provision for (benefit from) income taxes	1,372	(5,076)	1,271
Net (loss) income	$ 11,062	$ 7,601	$ (10,674)
Earnings Per Share, Basic	$ 0.25	$ 0.18	$ (0.26)
Earnings Per Share, Diluted	$ 0.25	$ 0.17	$ (0.26)
Weighted-average common shares outstanding - basic	43,822	42,649	41,662
Weighted-average common shares outstanding - diluted	44,878	43,495	41,662
Product [Member]
Net revenues:
Products	$ 140,762	$ 207,445	$ 205,107
Cost of revenues:
Products	84,222	109,799	110,758
Service [Member]
Net revenues:
Products	219,704	204,343	208,175
Cost of revenues:
Products	$ 47,924	$ 49,176	$ 55,560