Stock Based Compensation (Tables)
 3 Months Ended
Mar. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]  
Summary of stock option activity
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
Stock-based compensation expense
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
Stock option valuation assumptions
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%