Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Net sales	$ 406,184	$ 406,039	$ 335,764
Cost of sales	202,302	194,514	162,530
Gross profit	203,882	211,525	173,234
Operating expenses:
Selling and marketing	116,222	115,437	101,618
General and administrative	27,111	28,775	21,441
Research and development	15,446	13,919	9,904
Asset impairment charge	8,800	0	0
Total operating expenses	167,579	158,131	132,963
Operating income	36,303	53,394	40,271
Other income (expense):
Interest income	653	234	218
Interest expense	(1,552)	(1,928)	(22)
Other, net	301	(119)	(445)
Total other expense, net	(598)	(1,813)	(249)
Income from continuing operations before income taxes	35,705	51,581	40,022
Income tax expense	8,080	16,480	13,219
Income from continuing operations	27,625	35,101	26,803
Discontinued operations:
Loss from discontinued operations before income taxes	(1,713)	(1,077)	(601)
Income tax benefit of discontinued operations		(154)	(400)
Loss from discontinued operations	(1,358)	(923)	(201)
Net income	$ 26,267	$ 34,178	$ 26,602
Basic net income per share
Basic income per share from continuing operations (in dollars per share)	$ 0.90	$ 1.13	$ 0.86
Basic income (loss) per share from discontinued operations (in dollars per share)	(0.04)	(0.03)	(0.01)
Basic net income per share (in dollars per share)	0.86	1.10	0.85
Diluted net income per share
Diluted income per share from continuing operations (in dollars per share)	0.89	1.12	0.85
Diluted income (loss) per share from discontinued operations (in dollars per share)	(0.04)	(0.03)	(0.01)
Diluted net income per share (in dollars per share)	$ 0.85	$ 1.09	$ 0.84
Shares used in per share calculations:
Basic (in shares)	30,671	31,032	31,288
Diluted (in shares)	31,010	31,301	31,589