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Summary of Significant Accounting Policies (Narrative) (Details)	3 Months Ended								12 Months Ended
	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($) segment	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jan. 01, 2019 USD ($)
Revenue from External Customer [Line Items]
Cash equivalents, qualification, maximum original maturity of short-term investments									3 months
Customer deposit requirements, large custom contracts, maximum percentage									50.00%
Allowance for doubtful accounts	$ 291,000				$ 569,000				$ 291,000	$ 569,000
Revenues	16,160,000	$ 16,396,000	$ 18,204,000	$ 14,718,000	16,660,000	$ 15,913,000	$ 16,218,000	$ 18,902,000	65,478,000	67,693,000	$ 71,654,000
Impairment of goodwill									0	0
Product warranty reserves	22,000				65,000				22,000	65,000
Uncertain tax positions	0				$ 0				0	0
Additions to tax positions of prior years	547,000								547,000
Income tax penalties and interest accrued	$ 55,000								$ 55,000
Tax reform impact										18,400,000
Number of business segments | segment									1
Bill and Hold Arrangement
Revenue from External Customer [Line Items]
Revenues									$ 8,300,000	$ 4,600,000
Accounting Standards Update 2016-02 | Scenario, Forecast | Subsequent Event
Revenue from External Customer [Line Items]
Operating lease, right-of-use asset												$ 700,000
Operating lease, liability												$ 700,000
Tax Year 2017
Revenue from External Customer [Line Items]
Additions to tax positions of prior years									168,000
Tax Year 2016
Revenue from External Customer [Line Items]
Additions to tax positions of prior years									149,000
Tax Year 2015
Revenue from External Customer [Line Items]
Additions to tax positions of prior years									$ 230,000

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