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Equity Plans and Stock-Based Compensation (Tables)
6 Months Ended
Jun. 30, 2017
Share Based Compensation [Abstract]  
Option Activity under Stock-Based Compensation Plans

Option activity under our stock-based compensation plans during the six months ended June 30, 2017 was as follows (in thousands except per share amounts):

 

 

 

Shares Underlying  Outstanding Options

(in thousands)

 

 

Weighted-Average Exercise

Price Per Share

 

 

Weighted-Average Remaining Contractual Term (years)

 

 

Aggregate Intrinsic Value

(in thousands)

 

Balance at December 31, 2016

 

 

3,975

 

 

$

21.38

 

 

 

 

 

 

 

 

 

Options granted

 

 

279

 

 

 

6.08

 

 

 

 

 

 

 

 

 

Options exercised

 

 

-

 

 

 

-

 

 

 

 

 

 

 

 

 

Options cancelled:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Options forfeited (unvested)

 

 

(310

)

 

 

18.24

 

 

 

 

 

 

 

 

 

Options cancelled (vested)

 

 

(193

)

 

 

29.32

 

 

 

 

 

 

 

 

 

Balance at June 30, 2017

 

 

3,751

 

 

 

20.09

 

 

 

6.09

 

 

$

1,136

 

Vested and expected to vest at June 30, 2017

 

 

3,741

 

 

 

20.10

 

 

 

6.09

 

 

$

1,136

 

Exercisable at June 30, 2017

 

 

2,290

 

 

 

22.34

 

 

 

5.57

 

 

$

151

 

 

Summary of Restricted Stock Units Activity

Restricted stock unit activity under our stock-based compensation plans during the six months ended June 30, 2017 was as follows (in thousands except per share amounts):

 

 

Number of Shares (In thousands)

 

 

Weighted-Average Grant-Date Fair Value

 

Non-vested as of December 31, 2016

 

699

 

 

$

12.12

 

Granted

 

2,124

 

 

 

4.76

 

Vested

 

(171

)

 

 

18.62

 

Forfeited or expired

 

(93

)

 

 

12.25

 

Non-vested as of June 30, 2017

 

2,559

 

 

$

5.58

 

 

Fair Value-Based Measurements and Weighted-Average Assumptions

The fair value-based measurements and weighted-average assumptions used in the calculations of these measurements are as follows:

 

 

Stock Options

 

 

Stock Options

 

 

Employee Stock Purchase Plan

 

 

Three Months Ended

 

 

Six Months Ended

 

 

Six Months Ended

 

 

June 30,

 

 

June 30,

 

 

June 30,

 

 

2017

 

 

2016

 

 

2017

 

 

2016

 

 

2017

 

 

2016

 

Weighted-average fair value

$

3.90

 

 

$

10.25

 

 

$

4.12

 

 

$

9.79

 

 

$

2.37

 

 

$

8.18

 

Risk-free interest rate

 

1.8

%

 

 

1.5

%

 

 

1.9

%

 

 

1.4

%

 

 

0.9

%

 

 

0.6

%

Expected life (in years)

 

4.5

 

 

 

5.4

 

 

 

4.5

 

 

 

5.0

 

 

 

1.2

 

 

 

1.2

 

Volatility

 

0.9

 

 

 

0.7

 

 

 

0.9

 

 

 

0.7

 

 

 

1.0

 

 

 

0.6

 

 

Stock-Based Compensation Expense

The components of stock-based compensation expense were (in thousands):

 

 

Three Months Ended

 

 

Six Months Ended

 

 

June 30,

 

 

June 30,

 

 

2017

 

 

2016

 

 

2017

 

 

2016

 

Research and development

$

1,771

 

 

$

1,336

 

 

$

3,734

 

 

$

2,851

 

General and administrative

 

1,592

 

 

 

1,788

 

 

 

3,450

 

 

 

3,517

 

Total

$

3,363

 

 

$

3,124

 

 

$

7,184

 

 

$

6,368