Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 20,902	$ 18,947	$ 21,584	$ 18,882	$ 18,562	$ 22,933	$ 24,519	$ 22,185	$ 80,315	$ 88,199	$ 86,538
Cost of sales	10,636	9,981	11,513	9,079	8,599	10,819	12,560	10,641	41,209	42,619	43,937
Gross profit	10,266	8,966	10,071	9,803	9,963	12,114	11,959	11,544	39,106	45,580	42,601
Operating expenses:
Product development and engineering	5,075	4,937	5,125	5,344	5,112	4,901	5,310	5,125	20,481	20,448	20,833
Selling, general and administrative	7,719	6,931	7,007	8,017	6,570	7,281	7,379	7,736	29,674	28,966	35,080
Total operating expenses	12,794	11,868	12,132	13,361	11,682	12,182	12,689	12,861	50,155	49,414	55,913
Operating loss	(2,528)	(2,902)	(2,061)	(3,558)	(1,719)	(68)	(730)	(1,317)	(11,049)	(3,834)	(13,312)
Interest expense					(8)	(11)	(22)	(14)
Other income (loss), net	117	(180)	74	(277)	(21)	188	(296)	81	(266)	(48)	671
Loss from continuing operations before provision for income taxes	(2,411)	(3,082)	(1,987)	(3,835)	(1,748)	109	(1,048)	(1,250)	(11,315)	(3,937)	(12,665)
Provision for income taxes	194	31	36	61	2,783	(39)	77	50	322	2,871	1,873
Loss from continuing operations					(4,531)	148	(1,125)	(1,300)	(11,637)	(6,808)	(14,538)
Gain (loss) from discontinued operations					(2,185)	738	844	232	0	(371)	2,383
Net loss	$ (2,605)	$ (3,113)	$ (2,023)	$ (3,896)	$ (6,716)	$ 886	$ (281)	$ (1,068)	$ (11,637)	$ (7,179)	$ (12,155)
Net loss per share — basic and diluted (usd per share)	$ (0.38)	$ (0.45)	$ (0.29)	$ (0.56)					$ (1.69)	$ (1.02)	$ (1.66)
Basic and diluted weighted average shares (shares)	6,808	6,868	7,092	6,981					6,886	7,019	7,344
Net income loss per share — basic
From continuing operations (usd per share)					$ (0.65)	$ 0.02	$ (0.16)	$ (0.18)
From discontinued operations (usd per share)					(0.31)	0.11	0.12	0.03
Net loss per share — basic (usd per share)					(0.96)	0.13	(0.04)	(0.15)
Net Income (loss) per share — diluted
From continuing operations (usd per share)					(0.65)	0.02	(0.16)	(0.18)
From discontinued operations (usd per share)					(0.31)	0.11	0.12	0.03
Net loss per share — diluted (usd per share)					$ (0.96)	$ 0.13	$ (0.04)	$ (0.15)
Basic (shares)					6,980	6,978	6,988	7,131
Diluted (shares)					6,980	7,014	6,988	7,131
Revenue adjustment for write off of excess accrual for future product discounts	$ 500	$ 300	$ 400	$ 300
Increase in provision for income taxes related to increase in valuation allowance on deferred tax assets					$ 2,600