Quarterly Financial Information - Schedule of Quarterly Financial Information (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
Condensed Income Statements Captions [Line Items]
Total revenue	$ 5,553	$ 5,751	$ 6,497	$ 6,189	$ 5,319	$ 5,828	$ 6,180	$ 5,660	$ 23,990	$ 22,987
Total cost of revenue	1,695	1,928	2,113	2,198	1,799	1,918	2,185	2,134	7,934	8,036
Gross profit	$ 3,858	$ 3,823	$ 4,384	$ 3,991	$ 3,520	$ 3,910	$ 3,995	$ 3,526	16,056	14,951
Gross profit percent, service revenue	61.00%	58.00%	59.00%	55.00%	52.00%	55.00%	53.00%	57.00%
Gross profit percent, subscription revenue	79.00%	78.00%	80.00%	79.00%	80.00%	81.00%	80.00%	74.00%
Gross profit percent, total	69.00%	66.00%	67.00%	64.00%	66.00%	67.00%	65.00%	62.00%
Sales and marketing	$ 4,428	$ 4,538	$ 4,633	$ 5,246	$ 4,999	$ 4,839	$ 5,087	$ 4,950	18,845	19,875
Research, development and engineering	4,011	4,662	4,208	4,433	4,343	4,105	3,981	4,038	17,314	16,467
General and administrative	3,253	3,009	3,081	3,367	3,053	2,998	3,079	3,210	12,710	12,340
Operating loss	(7,834)	(8,386)	(7,538)	(9,055)	(8,875)	(8,032)	(8,152)	(8,672)	(32,813)	(33,731)
Net loss	(7,816)	(8,352)	(7,461)	(8,908)	$ (8,683)	$ (7,761)	$ (7,933)	$ (8,463)	(32,537)	(32,840)
Beneficial conversion feature	(11,443)								$ (11,443)	$ 0
Net loss attributable to common shares	$ (19,259)	$ (8,352)	$ (7,461)	$ (8,908)
Earnings (loss) per common share:
Loss per common share — basic	$ (1.27)	$ (0.68)	$ (0.62)	$ (0.74)	$ (0.73)	$ (0.65)	$ (0.68)	$ (0.74)	$ (3.41)	$ (2.79)
Loss per common share — diluted	$ (1.27)	$ (0.68)	$ (0.62)	$ (0.74)	$ (0.73)	$ (0.65)	$ (0.68)	$ (0.74)	$ (3.41)	$ (2.79)
Weighted average common shares outstanding—basic	15,222	12,241	12,108	12,037	11,967	11,924	11,665	11,487	12,906	11,762
Weighted average common shares outstanding—diluted	15,222	12,241	12,108	12,037	11,967	11,924	11,665	11,487	12,906	11,762
Service [Member]
Condensed Income Statements Captions [Line Items]
Total revenue	$ 2,899	$ 3,352	$ 3,892	$ 3,738	$ 2,700	$ 3,160	$ 3,575	$ 3,814	$ 13,881	$ 13,249
Total cost of revenue									5,827	6,013
Subscription [Member]
Condensed Income Statements Captions [Line Items]
Total revenue	$ 2,654	$ 2,399	$ 2,605	$ 2,451	$ 2,619	$ 2,668	$ 2,605	$ 1,846	10,109	9,738
Total cost of revenue									$ 2,107	$ 2,023