Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Oct. 01, 2016	Sep. 30, 2017	Oct. 01, 2016
Income Statement [Abstract]
Net sales	$ 402,646	$ 367,988	$ 1,081,218	$ 997,846
Cost of sales	149,181	135,645	404,675	385,168
Gross profit	253,465	232,343	676,543	612,678
Operating expenses:
Sales and marketing	174,800	158,024	488,564	443,477
General and administrative	32,645	28,278	95,233	86,202
Research and development	6,991	6,997	20,950	21,661
Total operating expenses	214,436	193,299	604,747	551,340
Operating income	39,029	39,044	71,796	61,338
Other expense, net	(248)	(255)	(668)	(581)
Income before income taxes	38,781	38,789	71,128	60,757
Income tax expense	13,178	13,044	21,842	20,627
Net income	$ 25,603	$ 25,745	$ 49,286	$ 40,130
Basic net income per share:
Net income per share – basic	$ 0.63	$ 0.56	$ 1.18	$ 0.86
Weighted-average shares – basic	40,755,000	45,621,000	41,740,000	46,705,000
Diluted net income per share:
Net income per share – diluted	$ 0.62	$ 0.56	$ 1.16	$ 0.85
Weighted-average shares – diluted	41,515,000	46,350,000	42,559,000	47,413,000