Revenue Recognition and Accounts Receivable - Summary of Consolidated Statement of Operations As Impact of Adoption (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenue Recognition And Accounts Receivable [Line Items]
Net sales	$ 111,708	$ 105,247	$ 331,964	$ 316,927
Cost of sales	24,020	23,717	71,002	69,475
Gross profit	87,688	81,530	260,962	247,452
Sales and marketing	49,898	47,493	151,695	146,496
Operating income	3,907	9,034	17,695	22,951
Income tax expense	115	(6,150)	(6,346)	(13,998)
Net income (loss) from continuing operations	$ (1,213)	$ 3,348	$ 4,949	$ 5,775
Net income (loss) from continuing operations per common share—basic	$ (0.07)	$ 0.18	$ 0.26	$ 0.32
Net income (loss) from continuing operations per common share—diluted	$ (0.07)	$ 0.18	$ 0.26	$ 0.31
Topic 606 [Member]
Revenue Recognition And Accounts Receivable [Line Items]
Net sales	$ 111,708		$ 331,964
Cost of sales	24,020		71,002
Gross profit	87,688		260,962
Sales and marketing	49,898		151,695
Other operating expenses	33,883		91,572
Operating income	3,907		17,695
Income tax expense	115		(6,346)
Net income (loss) from continuing operations	$ (1,213)		$ 4,949
Net income (loss) from continuing operations per common share—basic	$ (0.07)		$ 0.26
Net income (loss) from continuing operations per common share—diluted	$ (0.07)		$ 0.26
Topic 606 [Member] | Based on Historical Accounting under Topic 605 [Member]
Revenue Recognition And Accounts Receivable [Line Items]
Net sales	$ 109,512		$ 324,274
Cost of sales	23,784		68,975
Gross profit	85,728		255,299
Sales and marketing	49,766		151,741
Other operating expenses	33,883		91,572
Operating income	2,079		11,986
Income tax expense	677		(4,935)
Net income (loss) from continuing operations	$ (2,479)		$ 651
Net income (loss) from continuing operations per common share—basic	$ (0.13)		$ 0.04
Net income (loss) from continuing operations per common share—diluted	$ (0.13)		$ 0.03
Topic 606 [Member] | Impact of Adoption of Topic 606
Revenue Recognition And Accounts Receivable [Line Items]
Net sales	$ 2,196		$ 7,690
Cost of sales	236		2,027
Gross profit	1,960		5,663
Sales and marketing	132		(46)
Operating income	1,828		5,709
Income tax expense	(562)		(1,411)
Net income (loss) from continuing operations	$ 1,266		$ 4,298
Net income (loss) from continuing operations per common share—basic	$ 0.06		$ 0.22
Net income (loss) from continuing operations per common share—diluted	$ 0.06		$ 0.23