Revenue Recognition and Accounts Receivable - Summary of Consolidated Statement of Income As Impact of Adoption (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue Recognition And Accounts Receivable [Line Items]
Net sales	$ 121,078	$ 111,708	$ 111,547	$ 108,709	$ 116,896	$ 105,247	$ 108,942	$ 102,738	$ 453,042	$ 433,823	$ 409,788
Cost of sales	25,626	24,020	22,835	24,147	23,562	23,717	23,177	22,581	96,628	93,037	87,853
Gross profit	95,452	87,688	88,712	84,562	93,334	81,530	85,765	80,157	356,414	340,786	321,935
Sales and marketing									205,527	198,370	181,287
Operating income	12,402	3,907	5,915	7,870	17,860	9,034	7,998	5,919	30,094	40,811	21,067
Income tax expense									(9,074)	(29,100)	(15,527)
Net income from continuing operations	$ 8,871	$ (1,211)	$ 925	$ 5,226	$ 1,516	$ 3,348	$ 4,735	$ (2,308)	$ 13,811	$ 7,291	$ 3,497
Net income from continuing operations per common share—basic	$ 0.47	$ (0.07)	$ 0.05	$ 0.28	$ 0.08	$ 0.18	$ 0.26	$ (0.13)	$ 0.73	$ 0.40	$ 0.19
Net income from continuing operations per common share—diluted	$ 0.46	$ (0.07)	$ 0.05	$ 0.27	$ 0.08	$ 0.18	$ 0.26	$ (0.13)	$ 0.72	$ 0.39	$ 0.19
Topic 606 [Member]
Revenue Recognition And Accounts Receivable [Line Items]
Net sales									$ 453,042
Cost of sales									96,628
Gross profit									356,414
Sales and marketing									205,527
Other operating expenses									120,793
Operating income									30,094
Income tax expense									(9,074)
Net income from continuing operations									$ 13,811
Net income from continuing operations per common share—basic									$ 0.73
Net income from continuing operations per common share—diluted									$ 0.72
Topic 606 [Member] | Based on Historical Accounting under Topic 605 [Member]
Revenue Recognition And Accounts Receivable [Line Items]
Net sales									$ 445,343
Cost of sales									95,145
Gross profit									350,198
Sales and marketing									205,538
Other operating expenses									120,793
Operating income									23,867
Income tax expense									(7,656)
Net income from continuing operations									$ 9,002
Net income from continuing operations per common share—basic									$ 0.48
Net income from continuing operations per common share—diluted									$ 0.47
Topic 606 [Member] | Impact of Adoption of Topic 606
Revenue Recognition And Accounts Receivable [Line Items]
Net sales									$ 7,699
Cost of sales									1,483
Gross profit									6,216
Sales and marketing									(11)
Operating income									6,227
Income tax expense									(1,418)
Net income from continuing operations									$ 4,809
Net income from continuing operations per common share—basic									$ 0.25
Net income from continuing operations per common share—diluted									$ 0.25