Condensed Consolidated Statements of Operations (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 28, 2019	Sep. 29, 2018	Sep. 28, 2019	Sep. 29, 2018
Income Statement [Abstract]
Net sales	$ 474,778	$ 414,779	$ 1,257,186	$ 1,119,750
Cost of sales	178,388	164,262	481,377	442,868
Gross profit	296,390	250,517	775,809	676,882
Operating expenses:
Sales and marketing	213,133	188,458	568,799	511,481
General and administrative	35,098	29,385	102,466	89,947
Research and development	9,007	7,353	25,440	21,146
Total operating expenses	257,238	225,196	696,705	622,574
Operating income	39,152	25,321	79,104	54,308
Interest expense, net	3,131	1,836	8,968	3,814
Income before income taxes	36,021	23,485	70,136	50,494
Income tax expense	7,967	5,228	12,384	7,945
Net income	$ 28,054	$ 18,257	$ 57,752	$ 42,549
Basic net income per share:
Net income per share – basic	$ 0.96	$ 0.53	$ 1.93	$ 1.18
Weighted-average shares – basic	29,085,000	34,231,000	29,859,000	36,204,000
Diluted net income per share:
Net income per share – diluted	$ 0.94	$ 0.52	$ 1.88	$ 1.15
Weighted-average shares – diluted	29,796,000	35,039,000	30,688,000	37,077,000