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