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Income Taxes - Additional Information (Detail) - USD ($)
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Operating Loss Carryforwards [Line Items]    
Valuation allowances recognized in the current year $ 2,900,000 $ 16,400,000
Effect of tax act on valuation allowance   (38,800,000)
Effect of tax act on deferred tax assets   (38,800,000)
Effect of Tax Act $ 0 $ (971,000)
Statutory federal income tax rate 21.00% 34.00%
Internal Revenue Code related to annual use of operating loss carry forwards annual use of the Company’s net operating loss and research and development credit carryforwards may be limited in the event a cumulative change in ownership of more than 50% occurs within a rolling three-year period  
Internal Revenue Code ownership percentage change 50.00%  
Income tax benefit recognized related to uncertain tax positions $ 0 $ 0
Interest expense related to uncertain tax positions 0 0
Liability related to unrecognized tax benefits 0 $ 0
Domestic Tax Authority    
Operating Loss Carryforwards [Line Items]    
Net operating loss carryforwards $ 350,300,000  
Net operating loss expiration beginning date 2021  
Research and development tax credit carryforwards $ 9,400,000  
Tax credits expiration beginning date 2026  
California Franchise Tax Board    
Operating Loss Carryforwards [Line Items]    
Net operating loss carryforwards $ 38,900,000  
Net operating loss expiration beginning date 2028  
Research and development tax credit carryforwards $ 10,900,000  
Foreign Tax Authority    
Operating Loss Carryforwards [Line Items]    
Net operating loss carryforwards $ 53,100,000