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Share-Based Payment Arrangements (Tables)
 12 Months Ended
Dec. 31, 2015
Share-Based Payment Arrangements [Abstract]  
Assumptions used in computing the fair value of option grants
Under ASC 718 Compensation – Stock Compensation, the fair value of each non-qualified stock option award is estimated on the date of grant using the Black-Scholes option pricing model, which requires input assumptions noted in the following table. Ranges of assumptions for inputs are disclosed where the value of such assumptions varied during the related period. Historical volatilities are based upon daily quoted market prices of our common stock on The NASDAQ Stock Market LLC over a period equal to the expected term of the related equity instruments. We rely only on historical volatility since it provides the most reliable indication of future volatility. Future volatility is expected to be consistent with historical; historical volatility is calculated using a simple average calculation; historical data is available for the length of the option's expected term and a sufficient number of price observations are used consistently. Since our stock options are not traded on a public market, we do not use implied volatility. For 2015, 2014 and 2013 our expected term was calculated based upon historical data related to exercise and post-termination cancellation activity; accordingly, for grants issued to employees and directors and officers, we are using expected terms of 5.3 and 7.4 years, 5.3 and 7.5 years and 5.3 and 7.4 years, respectively. The expected term for options granted to non-employees was also calculated separately from stock options granted to employees and directors and officers and was ten years, which is the contractual term of those options. We have never paid dividends and do not expect to pay dividends in the future. Therefore, our dividend rate is zero. The risk-free rate for periods within the expected term of the options is based on the U.S. Treasury yield curve in effect at the time of grant. The following table presents assumptions used in computing the fair value of option grants during 2015, 2014 and 2013:

  
2015
  
2014
  
2013
      
Expected volatility
  
74 % – 84%
 
  
74 % – 84%
 
  
73 % – 90%
Expected dividends
 
 
Zero   
 
 Zero  
 
 Zero
Expected term (years)
  
5.3 – 7.4
   
5.3 – 7.5
   
5.3 – 10
Weighted average expected term (years)
  
6.04
   
5.93
   
5.96
Risk-free rate
  
1.64 % – 2.35%
 
  
1.64 % – 2.42%
 
  
0.76 % – 2.83%
Summary of option activity under the Plans
A summary of option activity under the Plans as of December 31, 2015 and changes during the year then ended is presented below:

Options
 
Shares
  
Weighted Average Exercise Price
  
Weighted Average Remaining Contractual Term (Yr.)
  
Aggregate Intrinsic Value
        
Outstanding at January 1, 2015
  
5,418
  
$
9.96
    
Granted
  
1,127
   
6.88
    
Exercised
  
(313
)
  
5.54
    
Forfeited
  
(433
)
  
5.76
    
Expired
  
(665
)
  
16.63
    
Outstanding at December 31, 2015
  
5,134
  
$
9.05
   
5.69
  
$
2,424
Exercisable at December 31, 2015
  
3,896
  
$
9.97
   
4.70
  
$
1,765
 
Compensation expense of shares, granted to both employees and non-employees
The total compensation expense of shares, granted to both employees and non-employees, under all of our share-based payment arrangements that was recognized in operations during 2015, 2014 and 2013 was:

  
2015
  
2014
  
2013
Recognized as:
     
Research and Development
 
$
1,099
  
$
1,843
  
$
2,012
General and Administrative
  
1,849
   
1,680
   
1,534
Total
 
$
2,948
  
$
3,523
  
$
3,546