CONDENSED CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 28, 2019	Jun. 29, 2018	Jun. 28, 2019	Jun. 29, 2018
Income Statement [Abstract]
Net sales	$ 39,664	$ 33,905	$ 72,247	$ 60,998
Cost of sales	9,765	8,678	18,168	16,340
Gross profit	29,899	25,227	54,079	44,658
Selling, general and administrative expenses:
General and administrative	7,508	6,196	14,345	11,967
Marketing and selling	11,682	10,659	21,825	18,113
Research and development	6,098	5,346	11,733	10,753
Total selling, general and administrative expenses	25,288	22,201	47,903	40,833
Operating income	4,611	3,026	6,176	3,825
Other income (expense), net:
Interest income (expense), net	259	(24)	530	(36)
Gain (loss) on foreign currency transactions	11	(520)	(237)	(597)
Royalty income	163	149	334	306
Other income, net	1	4	98	21
Total other income (expense), net	434	(391)	725	(306)
Income before income taxes	5,045	2,635	6,901	3,519
Provision for income taxes	1,131	805	1,620	1,106
Net income	$ 3,914	$ 1,830	$ 5,281	$ 2,413
Net income per share:
Basic	$ 0.09	$ 0.04	$ 0.12	$ 0.06
Diluted	$ 0.08	$ 0.04	$ 0.11	$ 0.06
Weighted average shares outstanding:
Basic	44,479	41,723	44,357	41,568
Diluted	46,733	43,999	46,842	43,654