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Stock-Based Compensation (Tables)
12 Months Ended
Dec. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]  
Summary of Stock Option Activity Under the 2012 and 2013 Plans

Stock option activity under the 2012 and 2013 plans is summarized as follows:

 

     Number
of Options
    Weighted-
Average
Exercise
Price
     Weighted-
Average
Remaining
Contractual
Term
(in years)
     Aggregate
Intrinsic
Value
(in thousands)
 

Outstanding at December 31, 2015

     1,229,339     $ 7.32        9.0      $ (4,679

Granted

     464,240       2.02        

Exercised

     (3,685     0.76        

Cancelled

     (112,878     4.97        
  

 

 

   

 

 

    

 

 

    

 

 

 

Outstanding at December 31, 2016

     1,577,016     $ 5.95        8.4      $ 71  
  

 

 

   

 

 

    

 

 

    

 

 

 

Vested and expected to vest at December 31, 2016

     1,492,341     $ 5.97        8.4      $ 69  
  

 

 

   

 

 

    

 

 

    

 

 

 

Exercisable at December 31, 2016

     561,693     $ 6.79        7.8      $ 52  
  

 

 

   

 

 

    

 

 

    

 

 

 
Additional Information about Stock Option Activity

Additional information about the Company’s stock option activity is as follows:

 

     Year Ended December 31,  
     2016      2015  

Weighted-average grant date fair value per share of employee option grants within the year

   $ 1.26      $ 4.08  

Cash received upon exercise of options

     3        39  

Schedule of Restricted Stock Awards Under the 2012 and 2013 Plans

Restricted stock awards under the 2012 and 2013 plans are summarized as follows:

 

     Number of
Shares
     Weighted Average
Grant Date Fair
Value
 

Unvested at December 31, 2015

     5,190      $ 1.07  

Vesting of restricted stock

     (3,301   
  

 

 

    

 

 

 

Unvested at December 31, 2016

     1,889      $ 0.83  
  

 

 

    

 

 

 
Summary of Stock-Based Compensation

Stock-based compensation is as follows:

 

     Year Ended  
     2016      2015  
     (in thousands)  

Research and development

   $ 491      $ 451  

General and administrative

     1,057        777  
  

 

 

    

 

 

 

Total stock-based compensation expense

   $ 1,548      $ 1,228  
  

 

 

    

 

 

 
Summary of Weighted-Average Assumptions Used in the Black-Scholes Option Pricing Model to Determine the Fair Value of the Employee Stock Option Grants

The weighted-average assumptions used in the Black-Scholes option pricing model to determine the fair value of the employee stock option grants were as follows:

 

     Year Ended  
     2016     2015  

Risk-free interest rate

     1.73     1.68

Expected volatility

     72.5     62.6

Expected term (in years)

     6.08       6.04  

Expected dividend yield

     0.0     0.0
Summary of Weighted-Average Assumptions Used in the Black-Scholes Option Pricing Model to Determine the Fair Value of the Non-Employee Stock Option Grants

The weighted-average assumptions used in the Black-Scholes option pricing model to determine the fair value of the non-employee stock option grants were as follows:

 

     Year Ended  
     2016     2015  

Risk-free interest rate

     1.57     1.79

Expected volatility

     63.5     63.2

Expected term (in years)

     7.00       6.16  

Expected dividend yield

     0.0     0.0