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Stock-Based Compensation Expense (Tables)
 6 Months Ended
Jun. 30, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]  
Stock Options Activity
A summary of share-based awards available for grant is as follows:

 
 
 
 
 
Shares
Available
for Grant
Balance, December 31, 2015
3,517,305

Additional shares reserved
1,000,000

Options granted
(302,236
)
Restricted stock units granted
(761,790
)
Options canceled
7,509

Restricted stock units canceled
87,621

Restricted stock units withheld for tax
154,682

Balance, June 30, 2016
3,703,091


Stock Option Awards

A summary of the stock option activity is as follows:

 
 
Options Outstanding
 
 
Number of
Stock Options
Outstanding
 
Weighted-
Average
Exercise
Price
Balance, December 31, 2015
2,641,592

 
$
6.47

Options granted
302,236

 
22.25

Options exercised
(29,167
)
 
6.30

Options canceled
(7,509
)
 
4.19

Balance, June 30, 2016
2,907,152

 
$
8.47
Restricted Stock Activity
Activity related to restricted stock units and awards is set forth below:

 
 
Number of Units and Awards
 
Weighted-
Average
Grant Date Fair Value
Balance, December 31, 2015
1,312,651

 
$
19.09

Restricted stock units granted
761,790

 
25.25

Restricted stock units vested
(419,703
)
 
14.68

Restricted stock units canceled
(87,621
)
 
21.44

Balance, June 30, 2016
1,567,117

 
$
23.14
Stock-based Compensation Expense
Stock-based compensation related to all of the Company's stock-based awards and employee stock purchases was recorded as an expense or a reduction to revenue and categorized as follows (in thousands):
 
 
Three Months Ended
 
Six Months Ended
 
June 30,
 
June 30,
 
2016
 
2015
 
2016
 
2015
Revenue
$
56

 
$
68

 
$
56

 
$
148

Cost of revenue
258

 
149

 
490

 
283

Research and development
507

 
392

 
1,008

 
742

Sales and marketing
1,820

 
1,345

 
3,203

 
2,896

General and administrative
1,979

 
1,129

 
4,065

 
3,164

Total stock-based compensation
$
4,620

 
$
3,083

 
$
8,822

 
$
7,233
Summary of Fair Value of Employee Stock Option Assumptions
The fair value of employee stock options was estimated using the following weighted-average assumptions:
 
 
Three Months Ended
 
Six Months Ended
 
June 30,
 
June 30,
 
2016
 
2015
 
2016
 
2015
Expected term
N/A
 
N/A
 
4.80 years

 
4.80 years

Expected volatility
N/A
 
N/A
 
63
%
 
63
%
Risk-free interest rate
N/A
 
N/A
 
1.21
%
 
1.29
%
Expected dividend yield
N/A
 
N/A
 
—
%
 
—
%