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Income Taxes (Narrative) (Details) - USD ($)
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Income Taxes [Line Items]      
Income tax provision (benefit)
Federal statutory tax rate 21.00% 35.00% 35.00%
Total unrecognized tax benefit $ 877,000 $ 512,000 $ 213,000
Accrued interest or penalties 0 $ 0 $ 0
Reduction in deferred tax assets due to tax act $ 4,700,000    
Scenario, Plan [Member]      
Income Taxes [Line Items]      
Federal statutory tax rate 21.00%    
Federal And California [Member]      
Income Taxes [Line Items]      
Net operating loss carryforward, expiration 2034    
Federal [Member]      
Income Taxes [Line Items]      
Net operating loss carryforwards $ 51,600,000    
Research and development credit carryforward $ 1,400,000    
Research and developmen tax credit carryforward, expiration 2035    
California [Member]      
Income Taxes [Line Items]      
Net operating loss carryforwards $ 51,000,000    
Research and development credit carryforward $ 1,200,000