Selected Quarterly Financial Data (Unaudited) - Unaudited Quarterly Data (Details) - 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
Statement of Operations Data:
Revenue	$ 4,281	$ 4,503	$ 4,640	$ 5,306	$ 5,854	$ 5,011	$ 3,971	$ 3,440	$ 18,730	$ 18,276
Cost of revenue	2,545	2,268	1,879	1,859	1,863	2,143	1,411	1,304	8,551	6,722
Gross profit	1,736	2,235	2,761	3,447	3,991	2,868	2,560	2,136	10,179	11,554
Operating expenses:
Research and development	1,324	1,128	920	851	818	1,523	656	561	4,223	3,558
Selling and marketing	1,080	1,383	851	891	798	893	477	301	4,205	2,469
General and administrative	1,402	1,205	1,140	1,486	1,116	1,147	457	1,889	5,233	4,609
Total operating expenses	3,806	3,716	2,911	3,228	2,732	3,563	1,590	2,751	13,661	10,636
Operating income (loss)	(2,070)	(1,481)	(150)	219	1,259	(695)	970	(615)	(3,482)	918
Interest and other income (expense)	97	145	120	119	57	5	(5,462)	13	481	(5,386)
Income (loss) before income taxes and equity loss in investee	(1,973)	(1,336)	(30)	338	1,316	(690)	(4,492)	(602)	(3,001)	(4,468)
Provision for (benefit from) income taxes	(596)	(415)	(110)	106	503	417			(1,015)	920
Income (loss) before equity loss in investee	(1,377)	(921)	80	232	813	(1,107)	(4,492)	(602)	(1,986)	(5,388)
Equity loss in investee	(247)	(172)	(105)						(524)	0
Net income (loss)	$ (1,624)	$ (1,093)	$ (25)	$ 232	$ 813	$ (1,107)	$ (4,492)	$ (602)	$ (2,510)	$ (5,347)
Net income (loss) per common share:
Basic	$ (0.09)	$ (0.06)		$ 0.01	$ 0.05	$ (0.44)	$ (5.49)	$ (0.02)
Diluted	$ (0.09)	$ (0.06)		$ 0.01	$ 0.05	$ (0.44)	$ (5.49)	$ (0.02)