STOCK-BASED COMPENSATION
 9 Months Ended
Sep. 30, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]  
STOCK-BASED COMPENSATION
STOCK-BASED COMPENSATION
As of September 30, 2016, there was a total of 2,004,755 shares of common stock available for future grants under our stock purchase and equity award or incentive plans. The following table summarizes the stock-based compensation expense by financial statement line item, employees and non-employees and type of award:
 
 
Three Months Ended September 30,
 
Nine Months Ended September 30,
 
 
2016
 
2015
 
2016
 
2015
Cost of revenue
 
$
44

 
$
200

 
$
124

 
$
517

Research and development
 
85

 
374

 
396

 
673

Sales and marketing
 
341

 
1,672

 
1,283

 
3,143

General and administrative
 
1,057

 
2,709

 
3,578

 
4,530

    Total
 
$
1,527

 
$
4,955

 
$
5,381

 
$
8,863

 
 
 
 
 
 
 
 
 
Employees
 
$
1,519

 
$
4,907

 
$
5,367

 
$
8,638

Non-employees
 
8

 
48

 
14

 
225

    Total
 
$
1,527

 
$
4,955

 
$
5,381

 
$
8,863

 
 
 
Three Months Ended September 30,
 
Nine Months Ended September 30,
 
 
2016
 
2015
 
2016
 
2015
Stock options
 
$
819

 
$
3,279

 
$
2,135

 
$
4,388

Restricted stock
 
346

 
—

 
692

 
—

Restricted stock units ("RSUs")
 
262

 
1,590

 
2,261

 
4,259

Employee Stock Purchase Plan
 
100

 
86

 
293

 
216

    Total
 
$
1,527

 
$
4,955

 
$
5,381

 
$
8,863


The following table summarizes stock option plans activity:
 
 
Shares
 
Weighted-
Average
Exercise
Price
 
Weighted-
Average
Remaining
Contractual
Term
(years)
 
Aggregate
Intrinsic
Value (1)
Outstanding at December 31, 2015
 
3,682,019

 
$
11.51

 
5.98
 
$
31,586

Granted
 
466,566

 
14.42

 

 

Exercised
 
(367,328
)
 
6.27

 

 

Expired
 
(5,771
)
 
5.73

 

 

Forfeited
 
(33,707
)
 
10.54

 

 

Outstanding at September 30, 2016(2)
 
3,741,779

 
$
12.40

 
6.27
 
$
22,150

Vested or expected to vest:
 
 
 
 
 
 
 
 
At September 30, 2016(2) (3)
 
3,461,891

 
$
12.57

 
6.36
 
$
19,995

Vested:
 
 
 
 
 
 
 
 
At September 30, 2016
 
1,743,949

 
$
11.73

 
5.76
 
$
11,205

(1) Calculated using the estimated per-share fair market value of our common stock on September 30, 2016 and December 31, 2015, which was $17.78, and $19.74, respectively.
(2) The total includes 993,740 performance-based options at September 30, 2016.
(3) Outstanding options, net of expected forfeitures.
A summary of RSU and restricted stock activity during the nine months ended September 30, 2016 is as follows:
 
 
RSUs
 
Shares of Restricted Stock
Outstanding at December 31, 2015
 
414,001

 
79,940

    Granted
 
15,101

 
165,217

    Vested (1) (2)
 
(351,029
)
 
(26,652
)
Outstanding at September 30, 2016
 
78,073

 
218,505

(1) Represents RSUs vested in 2016. These were net settled, which resulted in our withholding of 52,638 RSUs in lieu of withholding taxes during the nine months ended September 30, 2016, and are included in this total.
(2) Represents shares of restricted stock vested in 2016. 8,611 shares were returned to us in lieu of withholding taxes during the nine months ended September 30, 2016 and are reflected as Treasury Stock.