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Stock-Based Compensation (Tables)
 12 Months Ended
Dec. 31, 2012
Stock-Based Compensation [Abstract]  
Stock-based compensation expense

Our stock-based compensation expense for the last three fiscal years was as follows:

 

                         
    2012     2011     2010  

Research and development expense

   $ 1,280,298     $ 1,680,431     $ 2,034,007  

General and administrative expense

     1,597,836       1,580,506       1,895,627  
   

 

 

    

 

 

    

 

 

  

Total stock-based compensation expense and effect on net loss

   $ 2,878,134     $ 3,260,937     $ 3,929,634  
   

 

 

    

 

 

    

 

 

  
Schedule of Fair Value Option Award, Assumptions

The weighted-average assumptions used for the last three fiscal years are as follows:

 

                         
    2012     2011     2010  

Expected term (years)(1)

     6.4       7.4       7.2  

Risk-free interest rate(2)

     1.4 %      2.7 %      2.9 % 

Expected volatility(3)

     78.4 %      79.7 %      88.4 % 

Expected dividend yield(4)

     0 %      0 %      0 % 

 

(1) The expected term represents the period during which our stock-based awards are expected to be outstanding. We estimated this amount based on historical experience of similar awards, giving consideration to the contractual terms of the awards, vesting requirements, and expectation of future employee behavior, including post-vesting terminations.
(2) The risk-free interest rate is based on U.S. Treasury debt securities with maturities close to the expected term of the option as of the date of grant.
(3) Expected volatility is based on historical volatility over the most recent historical period equal to the length of the expected term of the option as of the date of grant.
(4) We have neither declared nor paid dividends on any share of common stock and we do not expect to do so in the foreseeable future.
Stock option activity

A summary of our stock option activity and related information for the last three fiscal years is as follows:

 

                                 
    Outstanding Options  
    Number of
Shares		     Weighted-
Average
Exercise Price		     Weighted-Average
Remaining
Contractual Term		     Aggregate
Intrinsic
Value(1)		  

Balance at December 31, 2009

     926,081     $ 22.80       6.2     $ 434,092  

Granted

     257,850     $ 10.70                  

Exercised

     (3,451 )    $ 5.70             $ 13,418  

Cancelled (forfeited and expired)

     (82,239 )    $ 20.50                  
   

 

 

                          

Balance at December 31, 2010

     1,098,241     $ 20.20       6.1     $ 398,219  

Granted

     3,750     $ 7.30                  

Exercised

     (1,692 )    $ 1.41             $ 11,293  

Cancelled (forfeited and expired)

     (224,801 )    $ 20.22                  
   

 

 

                          

Balance at December 31, 2011

     875,498     $ 20.13       5.5     $ —    

Granted

     —                            

Exercised

     (3,629 )    $ 1.00             $ 4,319  

Cancelled (forfeited and expired)

     (424,510 )    $ 20.86                  
   

 

 

                          

Balance at December 31, 2012

     447,359     $ 19.59       5.1     $ 2,175  
   

 

 

                          

Exercisable at December 31, 2012

     382,856     $ 21.06       4.8     $ 2,175  
   

 

 

                          

Vested and expected to vest(2)

     437,989     $ 19.77       5.1     $ 2,175  
   

 

 

                          

 

(1) Aggregate intrinsic value represents the value of the closing price per share of our common stock on the last trading day of the fiscal period in excess of the exercise price multiplied by the number of options outstanding or exercisable, except for the “Exercised” line, which uses the closing price on the date exercised.
(2) Number of shares includes options vested and those expected to vest net of estimated forfeitures.
Summary of changes in unvested options

The following is a summary of changes in unvested options:

 

                 

Unvested Options

   Number of
Options		     Weighted
Average
Grant Date Fair
Value		  

Unvested options at December 31, 2011

     152,192     $ 9.43  

Granted

     —         —    

Vested

     (63,911 )    $ 9.81  

Cancelled

     (23,778 )    $ 10.46  
   

 

 

          

Unvested options at December 31, 2012

     64,503     $ 8.67  
   

 

 

          
Weighted average exercise price and remaining term information about significant option groups outstanding

The following table presents weighted average exercise price and remaining term information about significant option groups outstanding at December 31, 2012:

 

                                 

Options Outstanding at December 31, 2012

  

Range of

Exercise Prices

   Number
Outstanding		     Weighted Average
Remaining
Term (Yrs.)		     Weighted Average
Exercise
Price		     Aggregate Intrinsic
Value at December 31,
2012		  

Less than $10.00

     13,828       2.8     $ 3.57     $ 2,175  

$10.00 - $19.99

     256,482       6.3     $ 12.70       —    

$20.00 - $29.99

     119,249       4.0     $ 23.18       —    

$30.00 - $39.99

     21,800       3.0     $ 36.22       —    

$40.00 - $49.99

     5,500       2.7     $ 46.51       —    

$50.00 - $59.99

     30,500       2.7     $ 53.94       —    
   

 

 

                    

 

 

  
      447,359       5.1     $ 19.59     $ 2,175  
   

 

 

                    

 

 

  

 

                 

Vested Options Outstanding at December 31, 2012

  

Range of Exercise Prices

   Number
Outstanding		     Weighted Average
Exercise Price		  

Less than $10.00

     11,443     $ 2.77  

$10.00 - $19.99

     194,364     $ 13.25  

$20.00 - $29.99

     119,249     $ 23.18  

$30.00 - $39.99

     21,800     $ 36.22  

$40.00 - $49.99

     5,500     $ 46.51  

$50.00 - $59.99

     30,500     $ 53.94  
   

 

 

          
      382,856     $ 21.06  
   

 

 

          
Summary of restricted stock unit activity

A summary of our restricted stock unit activity for the year ended December 31, 2012 is as follows:

 

                 
    Number of
RSUs		     Weighted Average
Grant Date Fair
Value		  

Outstanding at January 1, 2012

     357,542     $ 10.56  

Granted(1)

     1,358,000     $ 1.10  

Vested and exercised

     (171,062 )    $ 11.30  

Cancelled

     (10,280 )    $ 12.17  
   

 

 

          

Outstanding at December 31, 2012

     1,534,200     $ 2.10  
   

 

 

          

 

(1) 75,000 of these restricted stock units vest and convert into shares of our common stock after one year from the date of grant. 536,000 of these restricted stock units vest and convert into shares of our common stock over a three year period from the date of grant: one-third of the award will vest on each grant date anniversary following the grant. 747,000 of these restricted stock units vest and convert into shares of our common stock over a four year period from the date of grant: one-fourth of the award will vest on each grant date anniversary following the grant.
Summary of changes in outstanding SARs

The following is a summary of the changes in our outstanding SARs for the last three fiscal years:

 

                                                 
    2012     2011     2010  
    Number     Weighted
Average
Exercise
Price		     Number     Weighted
Average
Exercise
Price		     Number     Weighted
Average
Exercise
Price		  

Outstanding at January 1,

     115,187     $ 20.00       135,409     $ 20.00       143,085     $ 20.00  

Granted

     —         —         —         —         —         —    

Exercised

     —         —         —         —         —         —    

Forfeited

     (4,594 )              (20,222 )              (7,676 )         
   

 

 

            

 

 

            

 

 

          

Outstanding at December 31,

     110,593     $ 20.00       115,187     $ 20.00       135,409     $ 20.00  
   

 

 

            

 

 

            

 

 

          

Exercisable at December 31,

     110,593     $ 20.00       115,187     $ 20.00       135,409     $ 20.00