Supplementary Financial Information to Item 8. (Details) - USD ($) $ / shares in Units, $ 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	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Net sales	$ 3,118	$ 5,158	$ 5,172	$ 4,659	$ 4,727	$ 5,002	$ 6,011	$ 4,106	$ 18,107	$ 19,846	$ 30,998
Gross profit	19	1,281	1,296	816	1,622	1,137	1,501	561	3,412	4,821	7,677
Net loss	$ (3,000)	$ (1,920)	$ (1,801)	$ (2,390)	$ (1,858)	$ (1,773)	$ (3,114)	$ (4,522)	$ (9,111)	$ (11,267)	$ (16,887)
Net loss per share (basic and diluted) (in dollars per share)	$ (0.25)	$ (0.16)	$ (0.15)	$ (0.20)	$ (0.16)	$ (0.15)	$ (0.26)	$ (0.39)	$ (0.76)	$ (0.95)	$ (1.45)