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Equity Plans and Stock-Based Compensation (Tables)
3 Months Ended
Mar. 31, 2018
Share Based Compensation [Abstract]  
Option Activity under Stock-Based Compensation Plans

Option activity under our stock-based compensation plans during the three months ended March 31, 2018 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, 2017

 

 

3,555

 

 

$

19.56

 

 

 

 

 

 

 

 

 

Options granted

 

 

1,807

 

 

 

16.81

 

 

 

 

 

 

 

 

 

Options exercised

 

 

(25

)

 

 

14.67

 

 

 

 

 

 

 

 

 

Options cancelled:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Options forfeited (unvested)

 

 

(2

)

 

 

21.00

 

 

 

 

 

 

 

 

 

Options cancelled (vested)

 

 

(28

)

 

 

50.70

 

 

 

 

 

 

 

 

 

Balance at March 31, 2018

 

 

5,307

 

 

$

18.47

 

 

 

6.18

 

 

$

15,064

 

Vested and expected to vest at

  March 31, 2018

 

 

5,030

 

 

$

18.56

 

 

 

6.12

 

 

$

14,156

 

Exercisable at March 31, 2018

 

 

2,462

 

 

$

20.55

 

 

 

5.61

 

 

$

4,985

 

 

Summary of Restricted Stock Units Activity

Restricted stock unit activity under our stock-based compensation plans during the three months ended March 31, 2018 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, 2017

 

2,443

 

 

$

6.01

 

Granted

 

433

 

 

 

16.12

 

Vested

 

(681

)

 

 

5.33

 

Forfeited

 

-

 

 

 

-

 

Non-vested as of March 31, 2018

 

2,195

 

 

$

8.21

 

 

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

 

 

Employee Stock Purchase Plan

 

 

 

 

Three Months Ended

 

 

Three Months Ended

 

 

 

 

March 31,

 

 

March 31,

 

 

 

 

 

 

2018

 

 

2017

 

 

2018

 

 

2017

 

Weighted-average fair value

 

 

 

 

$

10.84

 

 

$

4.31

 

 

$

10.39

 

 

$

2.34

 

Risk-free interest rate

 

 

 

 

 

2.6

%

 

 

2.0

%

 

 

2.1

%

 

 

0.9

%

Expected life (in years)

 

 

 

 

 

4.5

 

 

 

4.5

 

 

 

1.3

 

 

 

1.3

 

Volatility

 

 

 

 

 

0.8

 

 

 

0.9

 

 

 

1.1

 

 

 

1.0

 

 

Stock-Based Compensation Expense

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

 

 

 

Three Months Ended

 

 

 

 

March 31,

 

 

 

 

 

 

2018

 

 

2017

 

Research and development

 

 

 

 

$

2,187

 

 

$

1,963

 

Selling, general and administrative

 

 

 

 

 

2,589

 

 

 

1,858

 

Cost of sales - product

 

 

 

 

 

23

 

 

 

-

 

Total

 

 

 

 

$

4,799

 

 

$

3,821