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Income Taxes, Components of Deferred Tax Assets (Liabilities) (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Deferred tax assets [Abstract]      
Reserves and accruals $ 45 $ 963  
Research and development credits and other credits 1,635 1,300  
Net operating loss carry forward 25,733 22,448  
Stock based compensation 8,857 9,260  
Other 26 54  
Total deferred tax assets 36,296 34,025  
Valuation allowance (36,296) (34,025)  
Deferred tax assets after valuation allowance 0 0  
Deferred tax liability [Abstract]      
Depreciation and amortization 0 0  
Total deferred tax liability 0 0  
Net deferred tax assets $ 0 $ 0  
Income Taxes [Abstract]      
Corporate federal tax rate 21.00% 35.00% 35.00%
Maximum [Member]      
Income Taxes [Abstract]      
Corporate federal tax rate   35.00%