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Income Taxes - Additional Information (Detail) - USD ($)
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Income Tax [Line Items]      
State income tax provision $ 1,300,000 $ 1,100,000 $ 1,300,000
Federal R&D credit carryforwards 26,300,000    
Increase in valuation allowance of deferred tax assets $ 33,500,000    
Tax rate 21.00% 35.00%  
Unrecognized tax reserves recorded during period $ 3,104,000 $ 361,000 363,000
Interest and/or penalties accrued 0 0  
Tax cuts and jobs act provisional adjustment 1,100,000 1,092,000  
Interest and/or penalties 0 $ 0 $ 0
Federal      
Income Tax [Line Items]      
Operating loss carryforwards $ 393,000,000    
Remaining net operating loss carryforward, expiration year 2026    
Federal | Expiring in 2025      
Income Tax [Line Items]      
Operating loss carryforwards $ 17,000,000    
State      
Income Tax [Line Items]      
Operating loss carryforwards $ 339,000,000    
Remaining net operating loss carryforward, expiration year 2025    
Research and development credit carryforwards with no expiration date $ 11,300,000    
State | Expiring in 2024      
Income Tax [Line Items]      
Net operating loss carryforwards with no expiration date 500,000    
State | Expiring in 2024 | Maximum      
Income Tax [Line Items]      
Operating loss carryforwards 100,000    
Foreign      
Income Tax [Line Items]      
Operating loss carryforwards 771,900,000    
Net operating loss carryforwards with no expiration date 3,400,000    
Foreign | Operating Loss Carryforwards Expiring 2022      
Income Tax [Line Items]      
Operating loss carryforwards 768,500,000    
Expire in 2019      
Income Tax [Line Items]      
Federal R&D credit carryforwards $ 100,000