Annual report pursuant to Section 13 and 15(d)

Income Taxes - Additional Information (Details)

v3.8.0.1
Income Taxes - Additional Information (Details) - USD ($)
 3 Months Ended 12 Months Ended
Dec. 31, 2017
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Income Tax Contingency [Line Items]          
Corporate tax rate     34.00% 34.00% 34.00%
Provisional net charge related to TCJA $ 7,578,000        
Tax expense (benefit) for change in valuation allowance     $ 767,000 $ 968,000 $ 1,164,000
Valuation allowance       767,000  
Unrecognized tax benefits, interest or penalties recognized     0 0 0
Unrecognized tax benefits that, if recognized, would affect the effective tax rate 1,062,000   1,062,000 934,000 $ 773,000
California          
Income Tax Contingency [Line Items]          
Research and development credits carryforwards     2,197,000    
Tax expense (benefit) for change in valuation allowance     767,000    
Valuation allowance       $ 767,000  
Federal          
Income Tax Contingency [Line Items]          
Net operating loss carryforwards 29,941,000   $ 29,941,000    
Net operating loss carryforwards expiration, beginning year     2023    
Research and development credits carryforwards     $ 2,181,000    
Research and development credits carryforwards expiration, beginning year     2022    
State          
Income Tax Contingency [Line Items]          
Net operating loss carryforwards $ 5,717,000   $ 5,717,000    
Net operating loss carryforwards expiration, beginning year     2028    
Scenario, Forecast          
Income Tax Contingency [Line Items]          
Corporate tax rate   21.00%