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Income Taxes - Additional Information (Detail) - USD ($)
 12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Income Tax Disclosure [Line Items]      
Increase (decrease) in deferred tax valuation allowance $ 40,700,000 $ 9,100,000  
Unrecognized tax benefits that would affect the effective tax rate if recognized 3,900,000 3,300,000 $ 2,800,000
Accrued interest and penalties related to unrecognized tax benefits 0 $ 0 $ 0
Federal Tax Authority [Member]      
Income Tax Disclosure [Line Items]      
Net operating loss carryforwards $ 192,000,000    
Operating loss carryforward expiration year 2030    
Federal Tax Authority [Member] | Research and Development Tax Credit [Member]      
Income Tax Disclosure [Line Items]      
Tax credit carryforwards $ 3,400,000    
Tax credit carryforward expiration year 2027    
State Tax Authority [Member]      
Income Tax Disclosure [Line Items]      
Operating loss carryforward expiration year 2025    
Other net operating losses $ 1,100,000    
State Tax Authority [Member] | California      
Income Tax Disclosure [Line Items]      
Net operating loss carryforwards $ 31,100,000    
Operating loss carryforward expiration year 2030    
State Tax Authority [Member] | Research and Development Tax Credit [Member]      
Income Tax Disclosure [Line Items]      
Tax credit carryforwards $ 3,800,000    
State Tax Authority [Member] | Minimum Tax Credit Carryforward [Member]      
Income Tax Disclosure [Line Items]      
Tax credit carryforwards $ 200,000