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Income Taxes - Additional Information (Details) - USD ($)
 12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Income Taxes [Line Items]    
Provision or benefit for income taxes $ 0 $ 0
Current federal or state income tax provision   0
Deferred federal or state income tax provision   0
Income Tax Contingency [Abstract]    
Valuation allowance 134,873,000 131,187,000
Increase in valuation allowance $ 3,700,000  
Net operating loss carryforwards, Expire date Begin to expire in 2019 and 2017  
State tax credit carryforwards $ 4,400,000  
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  
Excess tax benefits $ 1,300,000  
Liability for uncertain tax positions $ 0 $ 0
Period for material changes of liability for uncertain tax benefits 12 months  
Federal [Member]    
Income Tax Contingency [Abstract]    
Tax loss carryforwards $ 344,200,000  
Federal tax carry forward $ 4,900,000  
Federal tax credit carryforward, Expiration date Begin to expire in 2018  
State [Member]    
Income Tax Contingency [Abstract]    
Tax loss carryforwards $ 158,100,000