Quarterly Financial Data (unaudited) - Quarterly Financial Data (Unaudited) (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Total net sales	$ 26,153	$ 24,822	$ 25,753	$ 24,139	$ 23,288	$ 23,216	$ 22,389	$ 20,258	$ 100,867	$ 89,151	$ 78,352
Gross profit	18,251	17,577	17,516	17,353	16,194	17,019	15,367	14,356	70,697	62,936	54,166
Income (loss) from operations	6,321	5,053	5,536	4,193	3,909	5,344	3,783	3,300	21,103	16,336	11,513
Net income (loss)	$ 4,284	$ 5,042	$ 4,632	$ 3,219	$ 2,597	$ 3,229	$ 2,598	$ 2,166	$ 17,177	$ 10,590	$ 7,758
Basic:
Basic	$ 0.22	$ 0.26	$ 0.25	$ 0.17	$ 0.14	$ 0.17	$ 0.14	$ 0.12	$ 0.91	$ 0.57	$ 0.44
Diluted	$ 0.21	$ 0.25	$ 0.23	$ 0.16	$ 0.13	$ 0.17	$ 0.14	$ 0.11	$ 0.86	$ 0.55	$ 0.42