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Summary of Significant Accounting Policies - Narrative (Details) - USD ($) $ in Thousands | 12 Months Ended |  |  |
--- | --- | --- | --- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2019 | Jan. 01, 2019 | Dec. 31, 2015
Concentration Risk [Line Items] |  |  |  |  |  |
Cash and cash equivalents | $ 6,335 | $ 10,761 | $ 16,629 |  |  | $ 34,640
Restricted cash held | 342 | 342 | 342 |  |  |
Provision for slow-moving and obsolete inventories | (17) | 1,400 | (3,281) |  |  |
Inventory adjustments | 0 |  | 3,300 |  |  |
Operating loss carry-forwards | 8,700 | 37,300 | 10,600 |  |  |
Deferred tax assets, operating loss carry-forwards | $ 10,793 | 8,610 | 9,239 |  |  |
Impairment loss on equipment and software |  | $ 200 | $ 900 |  |  |
Antidilutive securities excluded from computation of earnings per share (number of shares) | 59,180 | 60,434 | 139,595 |  |  |
Advertising expense | $ 300 | $ 500 | $ 1,400 |  |  |
Operating lease, liability | $ 1,100 |  |  |  |  |
Customer concentration risk | Net sales |  |  |  |  |  |
Concentration Risk [Line Items] |  |  |  |  |  |
Concentration risk |  | 48.40% |  |  |  |
Customer concentration risk | Net sales | Northeast Ohio Hospital |  |  |  |  |  |
Concentration Risk [Line Items] |  |  |  |  |  |
Concentration risk |  | 18.30% | 10.90% |  |  |
Customer concentration risk | Net sales | Distributor To The U.S. Navy |  |  |  |  |  |
Concentration Risk [Line Items] |  |  |  |  |  |
Concentration risk | 41.90% | 17.30% | 36.50% |  |  |
Customer concentration risk | Net sales | Commercial Lighting Retrofit Company |  |  |  |  |  |
Concentration Risk [Line Items] |  |  |  |  |  |
Concentration risk |  | 12.80% |  |  |  |
Customer concentration risk | Net sales | U.S. Navy [Member] |  |  |  |  |  |
Concentration Risk [Line Items] |  |  |  |  |  |
Concentration risk | 46.20% | 22.00% | 43.10% |  |  |
Customer concentration risk | Accounts receivable | Northeast Ohio Hospital |  |  |  |  |  |
Concentration Risk [Line Items] |  |  |  |  |  |
Concentration risk |  | 21.00% |  |  |  |
Customer concentration risk | Accounts receivable | Distributor To The U.S. Navy |  |  |  |  |  |
Concentration Risk [Line Items] |  |  |  |  |  |
Concentration risk | 40.40% | 39.00% |  |  |  |
Customer concentration risk | Accounts receivable | Commercial Lighting Retrofit Company |  |  |  |  |  |
Concentration Risk [Line Items] |  |  |  |  |  |
Concentration risk |  | 17.40% |  |  |  |
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] |  |  |  |  |  |
Deferred tax assets, operating loss carry-forwards |  |  |  | $ 46,000 |  |
Domestic tax authority |  |  |  |  |  |
Concentration Risk [Line Items] |  |  |  |  |  |
Operating loss carry-forwards | $ 100,500 |  |  |  |  |
Deferred tax assets, operating loss carry-forwards | $ 46,000 |  |  |  |  |
Subsequent Event | Accounting Standards Update 2016-02 | Scenario, forecast |  |  |  |  |  |
Concentration Risk [Line Items] |  |  |  |  |  |
Operating lease, liability |  |  |  |  | $ 2,200 |
Operating lease, right-of-use asset |  |  |  |  | $ 2,200 |

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