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Income Taxes - Additional Information (Detail) - USD ($)
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Income Tax [Line Items]        
State income tax provision   $ 1,100,000 $ 1,300,000 $ 300,000
Federal R&D credit carryforwards   19,800,000    
Increase in valuation allowance of deferred tax assets   10,200,000    
Deferred tax benefit or expense related to remeasurement of deferred tax assets and liabilities   0    
Unrecognized tax reserves recorded during period   361,000 363,000 2,301,000
Interest and/or penalties accrued   0 0  
Tax cuts and jobs act provisional adjustment   1,092,000    
Interest and/or penalties   0 $ 0 $ 0
Scenario Forecast        
Income Tax [Line Items]        
Tax rate 21.00%      
Remeasurement of deferred tax balance $ 68,900,000      
Federal        
Income Tax [Line Items]        
Operating loss carryforwards   $ 407,100,000    
Remaining net operating loss carryforward, expiration year   2023    
Federal | Expiring in 2018        
Income Tax [Line Items]        
Operating loss carryforwards   $ 2,300,000    
State        
Income Tax [Line Items]        
Operating loss carryforwards   $ 340,000,000    
Remaining net operating loss carryforward, expiration year   2023    
Research and development credit carryforwards with no expiration date   $ 10,000,000    
State | Expiring in 2018 | Maximum        
Income Tax [Line Items]        
Operating loss carryforwards   100,000    
State | Expiring in 2023        
Income Tax [Line Items]        
Net operating loss carryforwards with no expiration date   200,000    
Foreign        
Income Tax [Line Items]        
Operating loss carryforwards   647,400,000    
Net operating loss carryforwards with no expiration date   3,600,000    
Foreign | Operating Loss Carryforwards Expiring 2022        
Income Tax [Line Items]        
Operating loss carryforwards   643,900,000    
Expire in 2018        
Income Tax [Line Items]        
Federal R&D credit carryforwards   $ 100,000