Annual report pursuant to Section 13 and 15(d)

Income Taxes - Additional Information (Detail)

v3.10.0.1
Income Taxes - Additional Information (Detail) - USD ($)
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Income Tax [Line Items]    
Provision for income taxes $ 0 $ 0
US federal corporate tax rate 21.00% 35.00%
Limitation of the deduction for net operating losses 80.00%  
Reduction in deferred tax assets   $ (38,200,000)
Net valuation allowance increase (decrease) $ 29,500,000 $ (32,700,000)
Cumulative change in ownership 50.00%  
Cumulative change in ownership period 3 years  
Significant change to its unrecognized tax benefits over the next twelve months $ 0  
Income tax examination years all years remain open for income tax examination by tax authorities  
Domestic Tax Authority [Member]    
Income Tax [Line Items]    
Net operating loss carryforward $ 332,700,000  
Research and development tax credit carry forwards 8,500,000  
Domestic Tax Authority [Member] | Orphan Drug [Member]    
Income Tax [Line Items]    
Research and development tax credit carry forwards $ 11,200,000  
Domestic Tax Authority [Member] | Minimum [Member]    
Income Tax [Line Items]    
NOL carry forward expiry date 2024  
Domestic Tax Authority [Member] | Maximum [Member]    
Income Tax [Line Items]    
NOL carry forward expiry date 2037  
State and Local Jurisdiction [Member]    
Income Tax [Line Items]    
Net operating loss carryforward $ 224,800,000  
Research and development tax credit carry forwards $ 4,500,000  
State and Local Jurisdiction [Member] | Minimum [Member]    
Income Tax [Line Items]    
NOL carry forward expiry date 2028  
State and Local Jurisdiction [Member] | Maximum [Member]    
Income Tax [Line Items]    
NOL carry forward expiry date 2038