Annual report pursuant to Section 13 and 15(d)

Income Taxes - Additional Information (Details)

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Income Taxes - Additional Information (Details) - USD ($)
 3 Months Ended 12 Months Ended
Dec. 31, 2017
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Income Tax Contingency [Line Items]        
Corporate tax rate   21.00% 21.00% 34.00%
Provisional net charge related to TCJA $ 7,578,000      
Additional adjustment to provisional amount 0      
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 1,889,000 $ 1,294,000 $ 1,062,000
Research and Development Credit | California        
Income Tax Contingency [Line Items]        
Research and development credits carryforwards   4,006,000    
Federal        
Income Tax Contingency [Line Items]        
Net operating loss carryforwards   54,883,000    
Net operating loss carryforwards, indefinite life   $ 46,426,000    
Net operating loss carryforwards expiration, beginning year   2033    
Research and development credits carryforwards expiration, beginning year   2022    
Federal | Research and Development Credit        
Income Tax Contingency [Line Items]        
Research and development credits carryforwards   $ 4,511,000    
State        
Income Tax Contingency [Line Items]        
Net operating loss carryforwards   $ 25,679,000    
Net operating loss carryforwards expiration, beginning year   2028