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