Income Taxes - Additional Information (Detail) - USD ($)
 12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2016
Dec. 31, 2015
Income Taxes [Line Items]        
Percentage of annual R&D credit for cash     65.00%  
Valuation allowance on the deferred tax asset 100.00% 100.00%    
Change in valuation allowance     $ 23,758,000 $ 10,317,000
Tax benefit on exercise of non-qualified stock options and disqualified disposition of incentive stock options     $ 840,000  
Unrecognized tax benefits, related interest and penalties $ 0 $ 0    
Tax examinations, description     Tax years 2006 through 2016 remain open to U.S. federal and state tax examinations.  
Earliest Tax Year [Member]        
Income Taxes [Line Items]        
Open tax years     2006  
Latest Tax Year [Member]        
Income Taxes [Line Items]        
Open tax years     2016  
Federal [Member]        
Income Taxes [Line Items]        
Net operating loss carryforwards 151,583,000   $ 151,583,000  
Federal [Member] | Earliest Tax Year [Member]        
Income Taxes [Line Items]        
Tax loss carryforwards expiration year     2026  
Federal [Member] | R&D Tax Credit Carryforwards [Member]        
Income Taxes [Line Items]        
Tax credit carryforwards 5,480,000   $ 5,480,000  
Federal [Member] | R&D Tax Credit Carryforwards [Member] | Earliest Tax Year [Member]        
Income Taxes [Line Items]        
Tax credit expiration year     2025  
State and Local [Member]        
Income Taxes [Line Items]        
Net operating loss carryforwards 145,222,000   $ 145,222,000  
State and Local [Member] | Earliest Tax Year [Member]        
Income Taxes [Line Items]        
Tax loss carryforwards expiration year     2027  
State and Local [Member] | R&D Tax Credit Carryforwards [Member]        
Income Taxes [Line Items]        
Tax credit carryforwards $ 810,000   $ 810,000