Annual report pursuant to Section 13 and 15(d)

Income Taxes - Additional Information (Detail)

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Income Taxes - Additional Information (Detail) - USD ($)
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Income Taxes Disclosure [Line Items]      
U.S. corporate income tax rate 21.00% 35.00%  
Valuation allowance recorded to offset income tax expense from revaluation of deferred tax assets and liabilities due to corporate tax rate change $ 0 $ 6,863,000  
Income tax expense from revaluation of deferred tax assets and liabilities due to change corporate tax rate   6,900,000  
Adjustment to provisional amounts related to enactment-date income tax effects of the tax act   0  
Income tax provision 0 0  
Increase in valuation allowance 2,800,000    
Unrecognized benefits 0 1,143,000 $ 0
Accrued interest or penalties 0 $ 0  
State      
Income Taxes Disclosure [Line Items]      
Research and development credits 200,000    
Federal      
Income Taxes Disclosure [Line Items]      
Net operating loss carryforwards $ 95,000,000    
Year net operating loss carryforwards begin to expire 2021    
Research and development credits $ 1,900,000    
Year research and development credits begin to expire 2022