Stock Based Compensation
 3 Months Ended
Mar. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]  
Stock Options
Stock Based Compensation
The Company’s stock option activity and related information for the three months ended March 31, 2014 was as follows (in thousands, except share and per share data):
 
 
 
 
 
 
 
Weighted-avg.
 
 
 
 Shares
 
 
 
 Weighted-avg.
 
Remaining
 
Aggregate
 
 Available
 
 Stock Options
 
 Exercise Price
 
Contractual
 
Intrinsic
 
 for Grant
 
 Outstanding
 
 Per Share
 
Life (in Years)
 
Value
 
 
 
 
 
 
 
 
 
 
 Balance at December 31, 2013
762,867

 
1,909,769

 
$
8.77

 
8.58
 
$
11,818

 Stock options granted
(35,000
)
 
35,000

 
$
12.29

 
 
 
 
 Stock options cancelled
61,802

 
(67,785
)
 
$
43.07

 
 
 
 
 Stock options exercised
—

 
(223,478
)
 
$
1.77

 
 
 
 
 Balance at March 31, 2014
789,669

 
1,653,506

 
$
8.38

 
9.02
 
$
5,578

 
 
 
 
 
 
 
 
 
 
At March 31, 2014:
 
 
 
 
 
 
 
 
 
    Vested and expected to vest
 
 
1,498,651

 
$
8.17

 
8.74
 
$
5,131

    Exercisable
 
 
218,856

 
$
11.79

 
6.28
 
$
1,504


The aggregate intrinsic value of options exercised under all option plans was $2.6 million and $11,000 for the three months ended March 31, 2014 and 2013, respectively, determined as of the date of option exercise.
The Company recognized stock based compensation expense as follows (in thousands):
 
Three Months Ended March 31,
 
2014
 
2013
Research and development
$
465

 
$
2

General and administrative
910

 
14

Total
$
1,375

 
$
16

Since December 20, 2004 (inception) to March 31, 2014, the Company has incurred $2.8 million of stock based compensation expense.
As of March 31, 2014, there were unrecognized compensation costs of $14.5 million related to stock options and the Company expects to recognize those costs over a weighted average period of 3.40 years.
Stock-based compensation cost for stock options is estimated at the grant date based on the fair-value using the Black-Scholes option pricing model. The fair value of employee stock options is being amortized on a straight-line basis over the requisite service period of the awards. The fair value of employee stock options was estimated using the following weighted-average assumptions:
 
 
 
 
 
 
Period From
 
 
 
 
 
 
December 20, 2004
 
 
Three Months Ended March 31,
 
(Inception) to
 
 
2014
 
2013
 
March 31, 2014
Risk-free interest rates
 
2.01%
 
—
 
0.06% - 2.02%
Expected life in years
 
6.08
 
—
 
0.25 - 6.25
Expected dividend yield
 
—
 
—
 
—
Expected volatility
 
102%
 
—
 
52% - 109%