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Income Taxes - Additional Information (Detail) - USD ($)
 12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Operating Loss Carryforwards [Line Items]      
Valuation allowances recognized in the current year $ 19,300,000 $ 15,400,000  
Statutory federal income tax rate 34.00% 34.00% 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 $ 239,300,000    
Net operating loss expiration dates 2029 through 2036    
Research and development tax credit carryforwards $ 4,800,000    
Tax credits expiration dates 2027 through 2036    
California Franchise Tax Board      
Operating Loss Carryforwards [Line Items]      
Net operating loss carryforwards $ 40,600,000    
Net operating loss expiration dates 2017 through 2036    
Research and development tax credit carryforwards $ 6,200,000    
Oregon Tax Authority      
Operating Loss Carryforwards [Line Items]      
Net operating loss carryforwards $ 2,500,000    
Net operating loss expiration dates 2030 through 2031    
Research and development tax credit carryforwards $ 100,000    
Tax credits expiration dates expire in 2020    
Foreign Tax Authority      
Operating Loss Carryforwards [Line Items]      
Net operating loss carryforwards $ 35,700,000