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Income Taxes (Additional Information) (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Tax Credit Carryforward [Line Items]    
Federal operating loss carryforwards $ 251.5  
State operating loss carryforwards 200.0  
Operating loss carryforwards, exercise of stock options 1.4  
Deferred income tax valuation   100.00%
Increase in valuation allowance 21.8 $ 24.2
Domestic Tax Authority    
Tax Credit Carryforward [Line Items]    
Research and development tax credit carryforwards 2.6  
State and Local Jurisdiction    
Tax Credit Carryforward [Line Items]    
Research and development tax credit carryforwards $ 2.5