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Income Taxes - Additional Information (Details) - USD ($)
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Income Taxes [Line Items]      
Provision or benefit for income taxes   $ 0 $ 0
Income Tax Contingency [Abstract]      
Valuation allowance   97,089,000 $ 134,873,000
Increase (decrease) in valuation allowance   $ (37,800,000)  
Corporate income tax rate   34.00% 34.00%
Net operating loss carryforwards, Expire date   Begin to expire in 2019 and 2017  
State tax credit carryforwards   $ 4,500,000  
Cumulative change in ownership   50.00%  
Period of net operating loss and R&D tax credit carry forwards to offset future taxable income   3 years  
Increase in income tax rate   $ 45,800,000  
Decrease in net deferred tax assets   (45,800,000)  
Liability for uncertain tax positions   $ 0 $ 0
Period for material changes of liability for uncertain tax benefits   12 months  
Maximum [Member]      
Income Tax Contingency [Abstract]      
Corporate income tax rate   35.00%  
Scenario Plan [Member]      
Income Tax Contingency [Abstract]      
Corporate income tax rate 21.00%    
Federal [Member]      
Income Tax Contingency [Abstract]      
Tax loss carryforwards   $ 365,900,000  
Federal tax carry forward   $ 5,100,000  
Federal tax credit carryforward, Expiration date   Begin to expire in 2018  
State [Member]      
Income Tax Contingency [Abstract]      
Tax loss carryforwards   $ 147,400,000