Quarterly Results of Operations (Unaudited) - Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019
Quarterly Financial Information Disclosure [Abstract]
Revenues, net	$ 18,626	$ 17,537	$ 16,153	$ 14,511	$ 14,688	$ 13,660	$ 13,164	$ 12,467	$ 66,827	$ 53,979
Gross profit	$ 16,223	$ 15,273	$ 14,070	$ 12,610	$ 12,763	$ 11,859	$ 11,379	$ 10,867	58,176	46,868
Gross margin	87.10%	87.10%	87.10%	86.90%	86.90%	86.80%	86.40%	87.20%
Income (loss) from operations	$ 489	$ 368	$ (2,220)	$ (3,265)	$ (2,569)	$ (3,900)	$ (4,287)	$ (6,448)	(4,628)	(17,204)
Net income (loss)	$ 310	$ 6,314	$ (2,525)	$ (3,580)	$ (2,812)	$ (4,144)	$ (4,468)	$ (6,726)	$ 519	$ (18,150)
Basic net income (loss) per share	$ 0.02	$ 0.33	$ (0.13)	$ (0.19)					$ 0.03	$ (1.00)
Diluted net income (loss) per share	$ 0.02	$ 0.32	$ (0.13)	$ (0.19)					$ 0.03	$ (1.00)
Basic and diluted net loss per share					$ (0.15)	$ (0.23)	$ (0.25)	$ (0.38)
Weighted average shares outstanding - basic	19,183	19,183	18,837	18,482	18,402	18,375	17,944	17,890	18,921	18,160
Weighted average shares outstanding - diluted	19,603	19,737	18,837	18,482					19,305	18,160