Stock-based Compensation (Tables)
 9 Months Ended
Sep. 30, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]  
Schedule of total stock-based compensation expense
Total stock-based compensation expense included in the accompanying condensed consolidated statements of operations for the periods presented, is as follows :
 
Three Months Ended
September 30,
 
Nine Months Ended
September 30,
 
2013

2014
 
2013
 
2014
 
(in thousands)
 
(in thousands)
Research and development
$
318


$
691


$
860


$
1,392

Sales and marketing
97


129


249


361

General and administrative
268


406


753


1,001

Total stock-based compensation expense
$
683


$
1,226


$
1,862


$
2,754
Summary of the status of options granted under all options
A summary of the stock option activity for the nine months ended September 30, 2014 is presented below:
 
Number of
Stock
Options
 
Weighted
Average
Exercise
Price
 
Aggregate
Intrinsic Value
(in thousands)
 
Weighted Average Remaining Contractual Term (in years)
Outstanding—January 1, 2014
5,770,168

 
$
3.85

 
 
 
 
Granted (1)
4,972,895

 
$
2.56

 
 
 
 
Exercised
(236,755
)
 
$
0.26

 
 
 
 
Forfeited (1)
(2,978,768
)
 
$
4.50

 
 
 
 
Outstanding—September 30, 2014
7,527,540

 
$
2.85

 
$
283

 
7.17
Vested and expected to vest—September 30, 2014
6,869,530

 
$
2.89

 
$
283

 
6.97
Vested and exercisable—September 30, 2014
3,341,870

 
$
3.18

 
$
281

 
4.55

Note:
(1) The number of options granted and forfeited includes options cancelled and replaced in conjunction with the modifications described below.
Summary of RSU activity
A summary of RSU activity for the nine months ended September 30, 2014, is as follows:
 
Number of
Shares
 
Weighted-Average
Grant Date Fair
Value
Unvested—January 1, 2014
45,000

 
$
5.46

Granted
913,638

 
$
2.22

Released
(10,250
)
 
$
5.64

Forfeited
(39,000
)
 
$
2.70

Unvested—September 30, 2014
909,388

 
$
2.32

Expected to vest—September 30, 2014
825,609

 
$
2.43