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Basis of Presentation and Summary of Significant Accounting Policies - Narrative (Details) - USD ($)
shares in Thousands, $ in Thousands
3 Months Ended 12 Months Ended
Apr. 01, 2016
Mar. 31, 2019
Mar. 31, 2018
Dec. 31, 2018
Jan. 01, 2019
Concentration Risk [Line Items]          
Operating lease liabilities   $ 1,867      
Operating lease right-of-use assets   1,682      
Operating lease, impairment loss   $ 186      
Securities excluded from net loss per share calculation (in shares)   28 90    
Warranty service periods 10 years        
Minimum          
Concentration Risk [Line Items]          
Warranty service periods   1 year      
Maximum          
Concentration Risk [Line Items]          
Warranty service periods   5 years      
Geographic concentration risk | United States          
Concentration Risk [Line Items]          
Concentration risk (less than for one percent)   97.00%      
Revenue | Geographic concentration risk | Countries outside of the United States          
Concentration Risk [Line Items]          
Concentration risk (less than for one percent)   1.00% 1.00%    
Distributor To The U.S. Navy | Revenue | Customer concentration risk          
Concentration Risk [Line Items]          
Concentration risk (less than for one percent)   22.00% 46.00%    
Distributor To The U.S. Navy | Accounts receivable | Customer concentration risk          
Concentration Risk [Line Items]          
Concentration risk (less than for one percent)   19.00%   40.00%  
Shipbuilder for U.S.Navy | Revenue | Customer concentration risk          
Concentration Risk [Line Items]          
Concentration risk (less than for one percent)   10.00%      
Shipbuilder for U.S.Navy | Accounts receivable | Customer concentration risk          
Concentration Risk [Line Items]          
Concentration risk (less than for one percent)   14.00%      
Commercial Lighting Retrofit Company | Revenue | Customer concentration risk          
Concentration Risk [Line Items]          
Concentration risk (less than for one percent)   30.00% 10.00%    
Commercial Lighting Retrofit Company | Accounts receivable | Customer concentration risk          
Concentration Risk [Line Items]          
Concentration risk (less than for one percent)   34.00%      
U.S. Navy | Revenue | Customer concentration risk          
Concentration Risk [Line Items]          
Concentration risk (less than for one percent)   32.00% 50.00%    
Accounting Standards Update 2016-02          
Concentration Risk [Line Items]          
Operating lease liabilities         $ 2,900
Operating lease right-of-use assets         $ 2,900
Facilities | 2017 Restructuring Plan          
Concentration Risk [Line Items]          
Reclassification upon adoption of Topic 842   $ 273