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Summary of Significant Accounting Policies - Narrative (Details) - USD ($) $ in Thousands | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2018 | Dec. 31, 2014
Concentration Risk [Line Items] |  |  |  |  |
Cash and cash equivalents | $ 10,761 | $ 16,629 | $ 34,640 |  | $ 7,435
Restricted cash held | 342 | 342 | 113 |  |
Inventory adjustments | (1,400) | 3,300 | 1,739 |  |
Operating loss carry-forwards |  | 10,600 |  |  |
Deferred tax assets, operating loss carry-forwards | 8,610 | 9,239 | 5,384 |  |
Impairment loss on equipment and software | $ 185 | $ 857 |  |  |
Antidilutive securities excluded from computation of earnings per share (number of shares) | 60,434 | 139,595 |  |  |
Advertising expense | $ 500 | $ 1,356 | $ 695 |  |
Customer concentration risk | Net sales |  |  |  |  |
Concentration Risk [Line Items] |  |  |  |  |
Concentration risk | 48.40% | 47.40% |  |  |
Customer concentration risk | Net sales | Northeast Ohio Hospital |  |  |  |  |
Concentration Risk [Line Items] |  |  |  |  |
Concentration risk | 18.00% | 11.00% |  |  |
Customer concentration risk | Net sales | Distributor To The U.S. Navy |  |  |  |  |
Concentration Risk [Line Items] |  |  |  |  |
Concentration risk |  | 36.00% | 59.00% |  |
Customer concentration risk | Net sales | Commercial Lighting Retrofit Company |  |  |  |  |
Concentration Risk [Line Items] |  |  |  |  |
Concentration risk | 13.00% |  |  |  |
Customer concentration risk | Net sales | Distributor To The U.S. Navy, Two |  |  |  |  |
Concentration Risk [Line Items] |  |  |  |  |
Concentration risk |  |  | 16.00% |  |
Customer concentration risk | Net sales | U.S. Navy [Member] |  |  |  |  |
Concentration Risk [Line Items] |  |  |  |  |
Concentration risk | 22.00% | 43.10% | 79.70% |  |
Customer concentration risk | Accounts receivable | Northeast Ohio Hospital |  |  |  |  |
Concentration Risk [Line Items] |  |  |  |  |
Concentration risk | 21.00% | 10.00% |  |  |
Customer concentration risk | Accounts receivable | Distributor To The U.S. Navy |  |  |  |  |
Concentration Risk [Line Items] |  |  |  |  |
Concentration risk | 39.00% | 63.00% |  |  |
Customer concentration risk | Accounts receivable | Commercial Lighting Retrofit Company |  |  |  |  |
Concentration Risk [Line Items] |  |  |  |  |
Concentration risk | 17.00% |  |  |  |
Minimum |  |  |  |  |
Concentration Risk [Line Items] |  |  |  |  |
Property and equipment, useful life | 2 years |  |  |  |
Warranty for finished goods, number of years | 1 year |  |  |  |
Maximum |  |  |  |  |
Concentration Risk [Line Items] |  |  |  |  |
Property and equipment, useful life | 15 years |  |  |  |
Warranty for finished goods, number of years | 10 years |  |  |  |
Scenario, forecast |  |  |  |  |
Concentration Risk [Line Items] |  |  |  |  |
Operating loss carry-forwards |  |  |  | $ 37,300 |
Domestic tax authority |  |  |  |  |
Concentration Risk [Line Items] |  |  |  |  |
Operating loss carry-forwards | $ 91,800 |  |  |  |
Deferred tax assets, operating loss carry-forwards | $ 37,300 |  |  |  |

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