Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 29, 2018	Sep. 30, 2017	Sep. 29, 2018	Sep. 30, 2017
Income Statement [Abstract]
Net sales	$ 414,779	$ 402,646	$ 1,119,750	$ 1,081,218
Cost of sales	164,262	149,181	442,868	404,675
Gross profit	250,517	253,465	676,882	676,543
Operating expenses:
Sales and marketing	188,458	174,800	511,481	488,564
General and administrative	29,385	32,645	89,947	95,233
Research and development	7,353	6,991	21,146	20,950
Total operating expenses	225,196	214,436	622,574	604,747
Operating income	25,321	39,029	54,308	71,796
Other expense, net	1,836	248	3,814	668
Income before income taxes	23,485	38,781	50,494	71,128
Income tax expense	5,228	13,178	7,945	21,842
Net income	$ 18,257	$ 25,603	$ 42,549	$ 49,286
Basic net income per share:
Net income per share – basic	$ 0.53	$ 0.63	$ 1.18	$ 1.18
Weighted-average shares – basic	34,231,000	40,755,000	36,204,000	41,740,000
Diluted net income per share:
Net income per share – diluted	$ 0.52	$ 0.62	$ 1.15	$ 1.16
Weighted-average shares – diluted	35,039,000	41,515,000	37,077,000	42,559,000