Other Accrued Liabilities (Details) - USD ($) $ in Thousands	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, 2016
Other Accrued Liabilities [Abstract]
Accrued warranty, current, see Note 1	$ 156				$ 109
Accrued compensation, including commissions and vacation	1,275				785
Accrued state sales use and other taxes	2,719				2,125
Distributor rights liability, current	0				85
Accrued professional fees and other accrued liabilities	350				477
Total other accrued liabilities	4,500	$ 4,247	$ 3,754	$ 3,541	$ 3,581	$ 3,233	$ 3,359	$ 3,266	$ 2,909
Income Tax Examination, Penalties and Interest Accrued [Abstract]
Estimated tax positions subject to audit	$ 801