Quarterly report pursuant to Section 13 or 15(d)

Stock-based Compensation

v2.4.0.8
Stock-based Compensation
 6 Months Ended
Jun. 30, 2014
Stock-based Compensation [Abstract]  
Stock-based Compensation
7.  Stock-based Compensation

In the six month ended June 30, 2014, the Board of Directors of the Company approved grants under the Company's Long Term Incentive Plan for an aggregate of 1,621,089 stock options and an aggregate of 1,299,164 RSUs to certain employees of the Company. The stock options vest monthly over four years, and the RSUs vest annually over three years, in equal increments.

The Company recognizes compensation expense for all stock-based payment awards made to the Company's employees, consultants and directors based on estimated fair values. The valuation of stock option awards is determined at the date of grant using the Black-Scholes Model. This model requires inputs such as the expected term of the option, expected volatility and risk-free interest rate. To establish an estimate of expected term, the Company considers the vesting period and contractual period of the award and its historical experience of stock option exercises, post-vesting cancellations and volatility. The estimate of expected volatility is based on the Company's historical volatility. The risk-free rate is based on the yield available on U.S. Treasury zero-coupon issues. The forfeiture rate impacts the amount of aggregate compensation for both stock options and RSUs. To establish an estimate of forfeiture rate, the Company considers its historical experience of option forfeitures and terminations.

The fair value of the stock options granted was estimated based on the following weighted average assumptions for the three and six months ended June 30, 2014 and 2013:

 
  
Three Months Ended June 30,
    
Six Months Ended June 30,
  
 
  
2014
    
2013
    
2014
    
2013
  
Dividend yield
    
0
%
    
0
%
    
0
%
    
0
%
Expected volatility
    
91
%
    
92
%
    
93
%
    
92
%
Risk-free interest rate
    
1.68
%
    
1.44
%
    
1.71
%
    
0.84
%
Expected term
  
5.6 years
    
5.6 years
    
5.6 years
    
5.6 years
  


Stock option activity for the six months ended June 30, 2014 was as follows:

 
  
Options
    
Weighted Average Exercise Price Per Share
    
Weighted Average Remaining Contractual Life (in years)
    
Aggregate Intrinsic Value (in thousands)
  
Options outstanding at December 31, 2013
    
7,218,241
    
$
8.42
      
6.75
    
$
18,213
  
Granted
    
1,621,089
      
7.11
                  
Exercised
    
(736,896
)
    
4.32
                  
Forfeited, expired or cancelled
    
(286,255
)
    
19.11
                  
Options outstanding at June 30, 2014
    
7,816,179
    
$
8.14
      
7.00
    
$
7,382
  
Options exercisable at June 30, 2014
    
4,684,553
    
$
10.34
      
5.72
    
$
4,278
  


The valuation of RSUs is determined at the date of grant using the closing stock price. To establish an estimate of forfeiture rate, the Company considers its historical experience of forfeitures and terminations.

Unvested RSU activity for the six months ended June 30, 2014 is summarized below:

 
  
   
Weighted-
  
 
  
Number of
    
Average Grant-
  
 
  
Shares
    
Date Fair Value
  
Unvested balance at December 31, 2013
    
1,738,037
    
$
2.73
  
Granted
    
1,299,164
      
6.47
  
Vested
    
(514,125
)
    
4.11
  
Forfeited
    
(158,286
)
    
3.87
  
Unvested balance at June 30, 2014
    
2,364,790
    
$
4.97
  


The following table shows total stock-based compensation expense included in the condensed consolidated statements of comprehensive loss for the three and six months ended June 30, 2014 and 2013 (in thousands):

 
  
Three Months Ended June 30,
    
Six Months Ended June 30,
  
 
  
2014
    
2013
    
2014
    
2013
  
Research and development
  
$
953
    
$
432
    
$
3,359
    
$
1,429
  
Selling, general and administrative
    
1,471
      
667
      
2,989
      
1,290
  
Total stock-based compensation expense
  
$
2,424
    
$
1,099
    
$
6,348
    
$
2,719