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, 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
Income Statement [Abstract]
Service revenue	$ 3,001	$ 2,986	$ 3,253	$ 3,696	$ 3,017	$ 3,252	$ 3,148	$ 3,250	$ 12,936	$ 12,667	$ 12,517
Subscription revenue	1,348	1,306	1,420	1,445	1,434	1,417	1,494	1,463	5,519	5,808	6,377
License revenue	509	4,385	914	950	729	907	815	867	6,758	3,318	3,295
Total revenue	4,858	8,677	5,587	6,091	5,180	5,576	5,457	5,580	25,213	21,793	22,189
Total cost revenue	2,057	2,072	2,120	2,309	2,051	2,162	2,094	2,190	8,558	8,497	8,947
Gross profit	$ 2,801	$ 6,605	$ 3,467	$ 3,782	$ 3,129	$ 3,414	$ 3,363	$ 3,390	16,655	13,296	13,242
Gross profit percent, service revenue	55.00%	55.00%	55.00%	56.00%	54.00%	55.00%	55.00%	56.00%
Gross profit percent, subscription revenue	58.00%	53.00%	62.00%	62.00%	61.00%	58.00%	60.00%	55.00%
Gross profit percent, license revenue	74.00%	97.00%	87.00%	88.00%	85.00%	88.00%	88.00%	89.00%
Gross profit percent, total	58.00%	76.00%	62.00%	62.00%	60.00%	61.00%	62.00%	61.00%
Sales and marketing	$ 4,572	$ 4,075	$ 3,997	$ 3,992	$ 3,132	$ 2,945	$ 2,856	$ 2,955	16,636	11,888	9,275
Research, development and engineering	3,932	4,108	3,936	3,459	3,419	3,291	3,379	3,305	15,435	13,394	12,465
General and administrative	2,614	2,442	2,239	2,385	2,113	2,039	1,976	2,170	9,680	8,298	7,954
Intellectual property	345	387	345	392	346	394	462	434	1,469	1,636	1,525
Operating loss	(8,662)	(4,407)	(7,050)	(6,446)	(5,881)	(5,255)	(5,310)	(5,474)	(26,565)	(21,920)	(17,977)
Net loss	$ (8,370)	$ (4,240)	$ (6,943)	$ (6,218)	$ (5,756)	$ (5,198)	$ (5,283)	$ (5,435)	$ (25,771)	$ (21,672)	$ (17,934)
Earnings (loss) per common share:
Loss per common share—basic	$ (0.76)	$ (0.39)	$ (0.68)	$ (0.61)	$ (0.57)	$ (0.55)	$ (0.62)	$ (0.64)	$ (2.44)	$ (2.36)	$ (2.19)
Loss per common share—diluted	$ (0.76)	$ (0.39)	$ (0.68)	$ (0.61)	$ (0.57)	$ (0.55)	$ (0.62)	$ (0.64)	$ (2.44)	$ (2.36)	$ (2.19)
Weighted average common shares outstanding—basic	11,046	10,797	10,266	10,161	10,111	9,506	8,587	8,533	10,571	9,188	8,198
Weighted average common shares outstanding—diluted	11,046	10,797	10,266	10,161	10,111	9,506	8,587	8,533	10,571	9,188	8,198