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Income Taxes - Narrative (Details) - USD ($)
 12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Income Tax Disclosure [Abstract]      
Income tax provision $ 0 $ 0  
Valuation allowance, DTA increase in the period 16,000,000    
Operating Loss Carryforwards [Line Items]      
Accrued interest or penalties related to uncertain tax positions 0    
Valuation allowance, DTA increase in the period 16,000,000    
Unrecognized tax benefits 1,917,000 1,407,000 $ 986,000
U.S. Federal      
Operating Loss Carryforwards [Line Items]      
Operating loss carryforwards 215,000,000 170,800,000  
U.S. Federal | Research and development credit carryforwards | Internal Revenue Service (IRS)      
Operating Loss Carryforwards [Line Items]      
Tax credit carryforward, amount 4,200,000 3,100,000  
U.S. State and Local      
Operating Loss Carryforwards [Line Items]      
Operating loss carryforwards 123,500,000 100,700,000  
U.S. State and Local | Research and development credit carryforwards | California Franchise Tax Board      
Operating Loss Carryforwards [Line Items]      
Tax credit carryforward, amount $ 3,400,000 $ 2,500,000