Stock-Based Compensation (Tables)
 12 Months Ended
Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]  
Summary of Employee and Nonemployee Stock Option Activity
A summary of employee and non-employee stock option activity for the years ended December 31, 2015, 2014 and 2013 is as follows:
 
 
 
Options Outstanding
 
Weighted-
Average
Remaining
Contractual
Term (in years)
 
Aggregate
Intrinsic
Value
(in thousands)
 
 
Number of
Shares
(in thousands)
 
Weighted-
Average
Exercise
Price
 
Outstanding January 1, 2013
 
553

 
$
12.76

 
7.13
 
$
1,142

Granted
 
427

 
14.57

 
 
 
 
Canceled or expired
 
(106
)
 
20.46

 
 
 
 
Outstanding December 31, 2013
 
874

 
$
10.83

 
7.75
 
$
3,139

Granted
 
1,154

 
10.41

 
 
 
 
Exercised
 
(30
)
 
6.61

 
 
 
 
Canceled or expired
 
(159
)
 
11.45

 
 
 
 
Outstanding December 31, 2014
 
1,839

 
$
10.58

 
8.49
 
$
618

Granted
 
312

 
$
9.77

 
 
 
 
Exercised
 
(4
)
 
$
5.37

 
 
 
 
Canceled or expired
 
(186
)
 
$
9.69

 
 
 
 
Outstanding December 31, 2015
 
1,961

 
$
10.55

 
7.68
 
$
—

Exercisable, December 31, 2015
 
958

 
$
10.09

 
6.61
 
$
—
Weighted-Average Assumptions Used to Estimate Fair Value of Options Granted
The following table presents the weighted-average assumptions used to estimate the fair value of options reaching their measurement date for non-employees during the periods presented:
 
 
 
Year Ended December 31,
 
 
2015
 
2014
 
2013
Volatility
 
70.38
%
 
71.76
%
 
75.68
%
Risk free interest rate
 
2.10
%
 
2.44
%
 
1.53
%
Dividend yield
 
—

 
—

 
—

Term (years)
 
8.73

 
9.68

 
7.68

The following table presents the weighted-average assumptions used to estimate the fair value of options granted to employees during the periods presented: 
 
 
Year Ended December 31,
 
 
2015
 
2014
 
2013
Volatility
 
60.69
%
 
70.17
%
 
76.60
%
Risk free interest rate
 
1.63
%
 
1.78
%
 
1.79
%
Dividend yield
 
—

 
—

 
—

Term (years)
 
6.13

 
5.98

 
6.14

Weighted-average fair value of options granted during the period
 
$
5.54

 
$
5.29

 
$
9.85
Nonvested Restricted Stock Shares Activity
The following table summarizes the activities for our non-vested restricted stock awards for the years ended December 31, 2015, 2014 and 2013:
 
 
 
 
Non-vested Restricted Stock Awards
 
 
 
 
Number of Shares (in thousands)
 
Weighted-Average Grant Date Fair Value
Non-vested at January 1, 2013
 
 
 
$
—

 
$
—

Granted
 
 
 
8

 
13.50

Vested
 
 
 
(3
)
 
15.39

Non-vested at December 31, 2013
 
 
 
$
5

 
$
12.55

Granted
 
 
 
220

 
9.01

Vested
 
 
 
(80
)
 
10.19

Forfeited/canceled
 
 
 
(12
)
 
12.04

Non-vested at December 31, 2014
 
 
 
$
133

 
$
8.14

Granted
 
 
 
48

 
9.50

Vested
 
 
 
(47
)
 
9.09

Forfeited/canceled
 
 
 
(13
)
 
9.03

Non-vested at December 31, 2015
 
 
 
121

 
8.25
Effects of Stock-Based Compensation Related to Stock Option and Restricted Stock Awards
The following table presents the effects of stock-based compensation related to stock option and restricted stock awards to employees and non-employees on our Statement of Operations during the periods presented (in thousands):
 
 
Year Ended December 31,
 
 
2015
 
2014
 
2013
Cost of revenues
 
$
233

 
$
149

 
$
41

Research and development
 
360

 
473

 
114

General and administrative
 
2,106

 
3,058

 
516

Sales and marketing
 
135

 
155

 
64

Total stock-based compensation
 
$
2,834

 
$
3,835

 
$
735