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Income Taxes - Additional Information (Details) - USD ($)
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Income Taxes [Line Items]    
Provision or benefit for income taxes $ 0 $ 0
Income Tax Contingency [Abstract]    
Valuation allowance 101,091,000 $ 97,089,000
Increase (decrease) in valuation allowance $ 4,000,000  
Corporate income tax rate 21.00% 34.00%
Net tax expense related to remeasurement of deferred tax assets and liabilities due to enactment-date effect of act $ 0 $ 0
Net operating loss carryforwards, Expire date Begin to expire in 2019 and 2028  
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  
Provisional amount of remeasured deferred tax assets and liabilities due to change in tax rate fully offset by valuation allowance   45,800,000
Liability for uncertain tax positions $ 0 $ 0
Period for material changes of liability for uncertain tax benefits 12 months  
Interest related to unrecognized tax benefits in interest expense and penalties $ 0  
Maximum [Member]    
Income Tax Contingency [Abstract]    
Corporate income tax rate   35.00%
Federal [Member]    
Income Tax Contingency [Abstract]    
Tax loss carryforwards 380,600,000  
Federal tax carry forward $ 5,200,000  
Federal tax credit carryforward, Expiration date Begin to expire in 2019  
Net operating losses $ 13,100,000  
Federal [Member] | Maximum [Member]    
Income Tax Contingency [Abstract]    
Percentage of federal net operating losses used to offset of future taxable income 80.00%  
State [Member]    
Income Tax Contingency [Abstract]    
Tax loss carryforwards $ 156,800,000