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Income Taxes - Additional Information (Detail) - USD ($)
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2007
Income Tax [Line Items]        
Gross federal R&D tax credit-related deferred tax assets derecognized $ 6,100,000      
Unrecognized tax benefit 1,871,000 $ 1,573,000 $ 1,475,000  
Tax-related penalties or interest recognized 0 0    
Uncertain tax positions 0 $ 0    
Federal Income Tax        
Income Tax [Line Items]        
Net operating loss carryforwards $ 163,800,000     $ 80,100,000
Net operating loss carryforwards expiration year 2032      
Tax credit carryforwards available to offset future federal tax liabilities $ 6,200,000      
Credit carryforward, expire period Dec. 31, 2037      
Net operating loss carryforward,derecognized $ 16,800,000      
State Income Tax        
Income Tax [Line Items]        
Net operating loss carryforwards $ 64,600,000      
Net operating loss carryforwards expiration year 2028      
Tax credit carryforwards available to offset future federal tax liabilities $ 4,700,000      
CALIFORNIA        
Income Tax [Line Items]        
Net operating loss carryforwards 14,200,000      
Net operating loss carryforward,derecognized $ 0