Annual report pursuant to Section 13 and 15(d)

Income Taxes - Additional Information (Details)

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Income Taxes - Additional Information (Details) - USD ($)
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Income Taxes [Line Items]      
Increased in valuation allowance $ 23,700,000 $ 23,700,000  
Interest or penalties accrued 0 0  
California      
Income Taxes [Line Items]      
Research and experimental credits carryforwards $ 1,300,000    
Research and experimental credits carryforwards, expiration The California research and experimental tax credits carry forward indefinitely until utilized.    
Federal      
Income Taxes [Line Items]      
Net operating loss carryforward subject to expiration $ 80,400,000 85,600,000  
Net operating loss carryforward not subject to expiration $ 5,000,000.0    
Net operating loss carryforwards latest expiration year 2026    
Net operating loss carryforwards     $ 75,500,000
Research and experimental credits carryforwards $ 1,200,000    
Research and experimental credits carryforwards, expiration The federal research and experimental tax credits will begin to expire, if not utilized, in 2026.    
State      
Income Taxes [Line Items]      
Net operating loss carryforwards latest expiration year 2021    
Net operating loss carryforwards $ 51,100,000 $ 55,000,000.0