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, 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
Condensed Income Statements Captions [Line Items]
Total revenue	$ 5,227	$ 4,914	$ 5,438	$ 5,613	$ 4,858	$ 8,677	$ 5,587	$ 6,091	$ 21,192	$ 25,213
Total cost of revenue	2,101	1,935	2,205	2,185	2,057	2,072	2,120	2,309	8,426	8,558
Gross profit	$ 3,126	$ 2,979	$ 3,233	$ 3,428	$ 2,801	$ 6,605	$ 3,467	$ 3,782	12,766	16,655
Gross profit percent, service revenue	52.00%	53.00%	54.00%	55.00%	55.00%	55.00%	55.00%	56.00%
Gross profit percent, subscription revenue	71.00%	69.00%	65.00%	69.00%	58.00%	53.00%	62.00%	62.00%
Gross profit percent, license revenue	74.00%	74.00%	77.00%	73.00%	74.00%	97.00%	87.00%	88.00%
Gross profit percent, total	60.00%	61.00%	59.00%	61.00%	58.00%	76.00%	62.00%	62.00%
Sales and marketing	$ 4,755	$ 4,741	$ 4,757	$ 4,887	$ 4,572	$ 4,075	$ 3,997	$ 3,992	19,140	16,636
Research, development and engineering	3,897	4,069	4,058	3,947	3,932	4,108	3,936	3,459	15,971	15,435
General and administrative	2,402	2,447	2,416	2,632	2,614	2,442	2,239	2,385	9,897	9,680
Intellectual property	334	328	305	315	345	387	345	392	1,282	1,469
Operating loss	(8,262)	(8,606)	(8,303)	(8,353)	(8,662)	(4,407)	(7,050)	(6,446)	(33,524)	(26,565)
Net loss	$ (8,014)	$ (8,342)	$ (8,038)	$ (8,112)	$ (8,370)	$ (4,240)	$ (6,943)	$ (6,218)	$ (32,506)	$ (25,771)
Earnings (loss) per common share:
Loss per common share — basic	$ (0.70)	$ (0.73)	$ (0.71)	$ (0.72)	$ (0.76)	$ (0.39)	$ (0.68)	$ (0.61)	$ (2.86)	$ (2.44)
Loss per common share — diluted	$ (0.70)	$ (0.73)	$ (0.71)	$ (0.72)	$ (0.76)	$ (0.39)	$ (0.68)	$ (0.61)	$ (2.86)	$ (2.44)
Weighted average common shares outstanding—basic	11,443	11,394	11,337	11,266	11,046	10,797	10,266	10,161	11,360	10,571
Weighted average common shares outstanding—diluted	11,443	11,394	11,337	11,266	11,046	10,797	10,266	10,161	11,360	10,571
Service [Member]
Condensed Income Statements Captions [Line Items]
Total revenue	$ 3,144	$ 2,787	$ 3,336	$ 3,507	$ 3,001	$ 2,986	$ 3,253	$ 3,696	$ 12,774	$ 12,936
Total cost of revenue									5,922	5,792
Subscription [Member]
Condensed Income Statements Captions [Line Items]
Total revenue	1,487	1,532	1,444	1,578	1,348	1,306	1,420	1,445	6,041	5,519
Total cost of revenue									1,907	2,264
License [Member]
Condensed Income Statements Captions [Line Items]
Total revenue	$ 596	$ 595	$ 658	$ 528	$ 509	$ 4,385	$ 914	$ 950	2,377	6,758
Total cost of revenue									$ 597	$ 502