Supplementary Financial Information to Item 8. (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Net sales	$ 3,531	$ 2,915	$ 3,082	$ 3,177	$ 3,118	$ 5,158	$ 5,172	$ 4,659	$ 12,705	$ 18,107	$ 19,846
Gross profit	957	1,028	(109)	98	19	1,281	1,296	816	1,974	3,412	4,821
Net loss	$ (1,308)	$ (946)	$ (2,254)	$ (2,865)	$ (3,000)	$ (1,920)	$ (1,801)	$ (2,390)	$ (7,373)	$ (9,111)	$ (11,267)
Net loss per share (basic and diluted) (in dollars per share)	$ (0.11)	$ (0.08)	$ (0.18)	$ (0.24)	$ (0.25)	$ (0.16)	$ (0.15)	$ (0.20)	$ (0.60)	$ (0.76)	$ (0.95)