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Summary of Significant Accounting Policies (Narrative) (Details) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2016 USD ($) | Sep. 30, 2016 USD ($) | Jun. 30, 2016 USD ($) | Mar. 31, 2016 USD ($) | Dec. 31, 2015 USD ($) | Sep. 30, 2015 USD ($) | Jun. 30, 2015 USD ($) | Mar. 31, 2015 USD ($) | Dec. 31, 2016 USD ($) segment | Dec. 31, 2015 USD ($) | Dec. 31, 2014 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 | $ 597,000 |  |  |  | $ 833,000 |  |  |  | $ 597,000 | $ 833,000 |
Total revenue | 16,703,000 | $ 16,181,000 | $ 17,194,000 | $ 21,576,000 | 25,755,000 | $ 21,193,000 | $ 24,230,000 | $ 24,741,000 | 71,654,000 | 95,919,000 | $ 96,974,000
Product warranty reserves | 103,000 |  |  |  | 103,000 |  |  |  | 103,000 | 103,000 |
Uncertain tax positions | $ 0 |  |  |  | $ 0 |  |  |  | $ 0 | 0 |
Number of business segments | segment |  |  |  |  |  |  |  |  | 1 |  |
Bill and Hold Arrangement |  |  |  |  |  |  |  |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Total revenue |  |  |  |  |  |  |  |  | $ 5,600,000 | $ 4,000,000 |

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