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Stock-Based Compensation (Tables)
 12 Months Ended
Dec. 31, 2015
Summary of Stock Options Activity under Plans and Related Information
A summary of the Company’s stock option activity under the Plans and related information is as follows:
 
Number of
Options
 
Weighted
Average
Exercise
Price
 
Weighted
Average
Remaining
Contractual
Term
(in years)
 
Aggregate
Intrinsic
Value(1)
 
 
 
 
 
 
 
(in thousands)
Balance at December 31, 2014
13,740,204

 
$
7.82

 
7.7
 
$
1,680

Granted
5,915,112

 
$
2.67

 
 
 
 
Exercised
(157,975
)
 
$
1.32

 
 
 
 
Forfeited, canceled or expired
(7,596,670
)
 
$
9.62

 
 
 
 
Balance at December 31, 2015
11,900,671

 
$
4.20

 
7.7
 
$
999

Options vested and exercisable at December 31, 2015
4,260,008

 
$
6.43

 
6.5
 
$
945

Options vested and expected to vest as of December 31, 2015
10,443,746

 
$
4.37

 
7.7
 
$
989

(1) 
The aggregate intrinsic value represents the value by which the Company’s closing stock price on the last trading day of the year ended December 31, 2015 exceeds the exercise price of the stock multiplied by the number of options outstanding or exercisable, excluding any that have a negative intrinsic value.
Summary of Stock Options Outstanding by Exercise Price Range
The following table presents the composition of options outstanding and vested and exercisable as of December 31, 2015:
 
Options Outstanding
 
Options Vested and Exercisable
Range of
Exercise Prices
Number of
Options
 
Weighted
Average
Exercise Price
 
Weighted
Average
Remaining
Contractual
Term
(in years)
 
Number of
Vested and
Exercisable
Options
 
Weighted
Average
Exercise
Price
 
Weighted
Average
Remaining
Contractual
Term
(in years)
$0.044-2.35
1,268,956

 
$
1.73

 
4.2
 
1,180,523

 
$
1.69

 
3.9
$2.46-2.54
3,108,991

 
$
2.47

 
8.9
 
691,191

 
$
2.47

 
8.6
$2.58-3.60
4,965,565

 
$
2.70

 
8.3
 
186,560

 
$
3.06

 
9.3
$6.79-9.72
1,173,475

 
$
8.12

 
6.5
 
990,176

 
$
8.12

 
6.2
$10.56-27.03
1,383,684

 
$
12.41

 
7.1
 
1,211,558

 
$
12.46

 
7.0
Totals
11,900,671

 
$
4.20

 
7.7
 
4,260,008

 
$
6.43

 
6.5
Stock-Based Compensation Expense Allocation
Stock-based compensation expense related to stock-based awards granted to employees and nonemployees were allocated to research and development and sales, general and administrative expense as follows (in thousands):
 
Year ended December 31,
 
2015
 
2014
 
2013
Research and development
$
4,562

 
$
7,407

 
$
5,917

Sales, general and administrative
11,122

 
18,142

 
12,736

Total
$
15,684

 
$
25,549

 
$
18,653
Schedule of Share-based Compensation, Restricted Stock Units Award Activity [Table Text Block]
Restricted Stock Units—A summary of the Company's restricted stock unit activity is as follows:
 
Number of
Shares
 
Weighted
Average
Grant Date
Fair Value
Unvested at December 31, 2014
1,812,332

 
$
10.91

Granted
1,139,531

 
$
2.82

Vested
(820,401
)
 
$
2.78

Canceled
(247,910
)
 
$
8.66

Unvested at December 31, 2015
1,883,552

 
$
9.85
Options to purchase common stock  
Weighted-Average Assumptions Used to Estimate Grant Date Fair Value of Stock-Based Awards
The grant date fair value of employee stock-based awards was estimated using the following weighted-average assumptions:  
 
Year ended December 31,
 
2015
 
2014
 
2013
Expected term (in years)
5.3-6.0
 
5.3-6.0
 
5.1-6.0
Volatility
67%-73%
 
51%-68%
 
60%-62%
Risk-free interest rate
0.86%-1.85%
 
1.58%-2.0%
 
0.8%-2.1%
Dividend yield
—%
 
—%
 
—%
Non Employee Stock Awards  
Weighted-Average Assumptions Used to Estimate Grant Date Fair Value of Stock-Based Awards
The fair value of non-employee stock-based awards was estimated using the following weighted-average assumptions:  
 
Year ended December 31,
 
2015
 
2014
 
2013
Expected term (in years)
8.2-8.6
 
8.3-8.6
 
7.8-8.9
Volatility
65%-67%
 
53%-64%
 
60%-61%
Risk-free interest rate
1.83%-2.21%
 
2.0%-2.5%
 
1.6%-2.8%
Dividend yield
—%
 
—%
 
—%