Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jul. 01, 2017	Jun. 30, 2018	Jul. 01, 2017
Income Statement [Abstract]
Net sales	$ 316,338	$ 284,673	$ 704,971	$ 678,572
Cost of sales	127,450	108,054	278,606	255,494
Gross profit	188,888	176,619	426,365	423,078
Operating expenses:
Sales and marketing	151,106	144,498	323,023	313,764
General and administrative	28,828	28,819	60,562	62,588
Research and development	6,868	6,363	13,793	13,959
Total operating expenses	186,802	179,680	397,378	390,311
Operating income (loss)	2,086	(3,061)	28,987	32,767
Other expense, net	1,453	282	1,978	420
Income (loss) before income taxes	633	(3,343)	27,009	32,347
Income tax (benefit) expense	(3,111)	(2,565)	2,717	8,664
Net income (loss)	$ 3,744	$ (778)	$ 24,292	$ 23,683
Basic net income (loss) per share:
Net income (loss) per share – basic	$ 0.10	$ (0.02)	$ 0.65	$ 0.56
Weighted-average shares – basic	36,138,000	41,716,000	37,191,000	42,233,000
Diluted net income (loss) per share:
Net income (loss) per share – diluted	$ 0.10	$ (0.02)	$ 0.64	$ 0.55
Weighted-average shares – diluted	36,844,000	41,716,000	38,096,000	43,080,000