Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016
Income Statement [Abstract]
Net sales		$ 396,753	$ 406,184	[1]	$ 406,039	[1]
Cost of sales		215,013	202,302	[1]	194,514	[1]
Gross profit		181,740	203,882	[1]	211,525	[1]
Operating expenses:
Selling and marketing		115,920	116,222	[1]	115,437	[1]
General and administrative		28,226	27,111	[1]	28,775	[1]
Research and development		16,825	15,446	[1]	13,919	[1]
Asset impairment charge		0	8,800	[1],[2]	0	[1],[2]
Total operating expenses		160,971	167,579	[1]	158,131	[1]
Operating income		20,769	36,303	[1]	53,394	[1]
Other income (expense):
Interest income		1,044	653	[1]	234	[1]
Interest expense		(1,051)	(1,552)	[1]	(1,928)	[1]
Other, net		239	301	[1]	(119)	[1]
Total other income (expense), net		232	(598)	[1]	(1,813)	[1]
Income from continuing operations before income taxes		21,001	35,705	[1]	51,581	[1]
Income tax expense		5,891	8,080	[1]	16,480	[1]
Income from continuing operations		15,110	27,625	[1],[2]	35,101	[1],[2]
Discontinued operations:
Loss from discontinued operations before income taxes		(206)	(1,713)	[1]	(1,077)	[1]
Income tax expense (benefit) of discontinued operations	[1]		(355)		(154)
Loss from discontinued operations		(452)	(1,358)	[1],[2]	(923)	[1],[2]
Net income		$ 14,658	$ 26,267	[1],[2]	$ 34,178	[1],[2]
Basic net income per share(1)
Basic income per share from continuing operations (in dollars per share)		$ 0.50	$ 0.90	[1]	$ 1.13	[1]
Basic income (loss) per share from discontinued operations (in dollars per share)		(0.02)	(0.04)	[1]	(0.03)	[1]
Basic net income per share (in dollars per share)	[3]	0.49	0.86	[1]	1.10	[1]
Diluted net income per share(1)
Diluted income per share from continuing operations (in dollars per share)		0.50	0.89	[1]	1.12	[1]
Diluted income (loss) per share from discontinued operations (in dollars per share)		(0.01)	(0.04)	[1]	(0.03)	[1]
Diluted net income per share (in dollars per share)	[3]	$ 0.48	$ 0.85	[1]	$ 1.09	[1]
Shares used in per share calculations:
Basic (in shares)		30,099	30,671	[1]	31,032	[1]
Diluted (in shares)		30,355	31,010	[1]	31,301	[1]

[1] See Note 4.

[2] See Note 4.

[3] May not add due to rounding.