Quarterly Financial Data - Condensed Consolidated Statement of Operations (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
Quarterly Financial Information Disclosure [Abstract]
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
Operating expense	83,050	83,781	82,797	76,692	75,474	72,496	77,767	74,238	326,320	299,975
Operating income	12,402	3,907	5,915	7,870	17,860	9,034	7,998	5,919	30,094	40,811	21,067
Net income (loss) 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 (loss)	$ 8,871	$ (1,211)	$ 925	$ 5,226	$ 1,568	$ 3,456	$ 3,853	$ (2,654)	$ 13,811	$ 6,223	$ 3,056
Net income (loss) per common share — basic:
Net income (loss) from continuing operations	$ 0.47	$ (0.07)	$ 0.05	$ 0.28	$ 0.08	$ 0.18	$ 0.26	$ (0.13)	$ 0.73	$ 0.40	$ 0.19
Net income (loss)	0.47	(0.07)	0.05	0.28	0.09	0.19	0.21	(0.15)	0.73	0.34	0.17
Net income (loss) per common share — diluted:
Net income (loss) from continuing operations	0.46	(0.07)	0.05	0.27	0.08	0.18	0.26	(0.13)	0.72	0.39	0.19
Net income (loss)	$ 0.46	$ (0.07)	$ 0.05	$ 0.27	$ 0.08	$ 0.19	$ 0.21	$ (0.15)	$ 0.72	$ 0.34	$ 0.17