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Equity Incentive Plans and Stock Based Compensation (Tables)
 12 Months Ended
Dec. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]  
Stock Option Activity Under Equity Incentive Plan

Activity under the 2004 and 2014 Plans is set forth below:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Weighted

 

 

 

Shares

 

 

Outstanding Options

 

 

Average

 

 

 

Available

 

 

Number of

 

 

Exercise

 

 

Exercise

 

 

 

for Grant

 

 

Shares

 

 

Price

 

 

Price

 

Balances, December 31, 2012

 

 

498,411

 

 

 

5,098,972

 

 

$

0.42–7.75

 

 

$

3.18

 

Additional shares reserved

 

 

1,250,000

 

 

 

—

 

 

 

 

 

 

 

 

 

Options granted

 

 

(1,663,500

)

 

 

1,663,500

 

 

4.45–5.58

 

 

 

5.10

 

Options exercised

 

 

—

 

 

 

(145,641

)

 

0.79–3.46

 

 

 

1.56

 

Options canceled

 

 

90,325

 

 

 

(90,325

)

 

1.44–7.75

 

 

 

6.49

 

Balances, December 31, 2013

 

 

175,236

 

 

 

6,526,506

 

 

$

0.42–7.75

 

 

$

3.66

 

Additional shares reserved

 

 

7,250,000

 

 

 

—

 

 

 

 

 

 

 

 

 

Shares expired

 

 

(1,286,025

)

 

 

—

 

 

 

 

 

 

 

 

 

Options granted

 

 

(1,895,250

)

 

 

1,895,250

 

 

2.91–4.99

 

 

 

3.78

 

Options exercised

 

 

—

 

 

 

(73,282

)

 

0.64–4.90

 

 

 

1.43

 

Options canceled

 

 

179,532

 

 

 

(179,532

)

 

1.64–6.18

 

 

 

4.63

 

Balances, December 31, 2014

 

 

4,423,493

 

 

 

8,168,942

 

 

$

0.42–7.75

 

 

$

3.69

 

Additional shares reserved

 

 

—

 

 

 

—

 

 

 

 

 

 

 

 

 

Options granted

 

 

(2,290,500

)

 

 

2,290,500

 

 

0.48-5.06

 

 

 

4.36

 

Options exercised

 

 

—

 

 

 

(99,759

)

 

0.79-4.90

 

 

 

1.75

 

Options canceled

 

 

1,327,547

 

 

 

(1,327,547

)

 

1.30-7.75

 

 

 

4.39

 

Balances, December 31, 2015

 

 

3,460,540

 

 

 

9,032,136

 

 

$

0.42–7.75

 

 

$

3.77

 

 
Stock Options Outstanding and Exercisable by Exercise Price

At December 31, 2015, stock options outstanding and exercisable by exercise price were as follows:

 

 

 

Options Outstanding

 

 

Options Exercisable

 

Range of

Exercise

Prices

 

Number

Outstanding

 

 

Weighted

Average

Remaining

Contractual

Life (Years)

 

 

Weighted

Average

Exercise

Price

 

 

Number

Exercisable

 

 

Weighted

Average

Exercise

Price

 

$0.42-$1.38

 

 

534,650

 

 

 

2.20

 

 

$

1.10

 

 

 

522,650

 

 

$

1.11

 

$1.44-$1.44

 

 

1,331,064

 

 

 

4.01

 

 

$

1.44

 

 

 

1,331,064

 

 

$

1.44

 

$1.49-$3.46

 

 

1,428,718

 

 

 

4.49

 

 

$

1.97

 

 

 

1,397,258

 

 

$

1.94

 

$3.62-$3.62

 

 

1,164,013

 

 

 

7.37

 

 

$

3.62

 

 

 

641,099

 

 

$

3.62

 

$3.87-$5.06

 

 

2,011,782

 

 

 

8.03

 

 

$

4.46

 

 

 

766,498

 

 

$

4.52

 

$5.09-$7.75

 

 

2,561,909

 

 

 

5.50

 

 

$

6.09

 

 

 

2,225,216

 

 

$

6.17

 

$0.42-$7.75

 

 

9,032,136

 

 

 

5.79

 

 

$

3.77

 

 

 

6,883,785

 

 

$

3.59

 

 
Stock-Based Compensation Expense

Stock-based compensation expense, which consists of the compensation cost for employee stock options and ESPP, and the value of options issued to non-employees for services rendered, was allocated to research and development and general and administrative in the consolidated statements of operations as follows (in thousands):

 

 

 

Years Ended December 31,

 

 

 

2015

 

 

2014

 

 

2013

 

Stock-based compensation expense:

 

 

 

 

 

 

 

 

 

 

 

 

Research and development

 

$

4,090

 

 

$

3,123

 

 

$

2,562

 

General and administrative

 

 

2,711

 

 

 

2,365

 

 

 

2,360

 

 

 

$

6,801

 

 

$

5,488

 

 

$

4,922

 

 
Weighted-Average Fair Value Valuation Assumptions

The fair value of employee stock options and employee purchase rights under the Company’s 2004 Purchase Plan was estimated using the following weighted-average assumptions for the years ended December 31, 2015, 2014 and 2013:

 

 

 

Years Ended December 31,

 

 

 

2015

 

 

2014

 

 

2013

 

Employee Stock Options

 

 

 

 

 

 

 

 

 

 

 

 

Risk-free interest rate

 

 

1.70

%

 

 

1.83

%

 

 

1.14

%

Expected life (in years)

 

 

5.99

 

 

 

5.98

 

 

 

5.97

 

Dividend yield

 

 

—

 

 

 

—

 

 

 

—

 

Volatility

 

 

83

%

 

 

94

%

 

 

101

%

Weighted-average fair value of stock options granted

 

$

3.06

 

 

$

2.89

 

 

$

4.04

 

Employee Stock Purchase Plan

 

 

 

 

 

 

 

 

 

 

 

 

Risk-free interest rate

 

 

0.39

%

 

 

0.20

%

 

 

0.19

%

Expected life (in years)

 

 

1.24

 

 

 

1.24

 

 

 

1.25

 

Dividend yield

 

 

—

 

 

 

—

 

 

 

—

 

Volatility

 

 

50

%

 

 

49

%

 

 

77

%

Weighted-average fair value of ESPP purchase rights

 

$

1.58

 

 

$

1.60

 

 

$

2.27

 

 
Non-employee Stock-based Compensation Expense  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]  
Weighted-Average Fair Value Valuation Assumptions

The fair value of the stock options granted were revalued at each reporting date using the Black-Scholes valuation model as prescribed by ASC 505-50 Equity-Based Payments to Non-Employees using the following assumptions:

 

 

 

Years Ended December 31,

 

 

 

2015

 

 

2014

 

 

2013

 

Risk-free interest rate

 

 

2.14

%

 

 

2.52

%

 

 

2.51

%

Expected life (in years)

 

 

10

 

 

 

10

 

 

 

10

 

Dividend yield

 

 

—

 

 

 

—

 

 

 

—

 

Expected volatility

 

 

103

%

 

 

97

%

 

 

100

%