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Equity Plans and Stock-Based Compensation (Tables)
9 Months Ended
Sep. 30, 2018
Share Based Compensation [Abstract]  
Option Activity under Stock-Based Compensation Plans

Option activity under our stock-based compensation plans during the nine months ended September 30, 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

 

 

2,386

 

 

 

16.56

 

 

 

 

 

 

 

 

 

Options exercised

 

 

(40

)

 

 

11.95

 

 

 

 

 

 

 

 

 

Options cancelled:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Options forfeited (unvested)

 

 

(139

)

 

 

13.89

 

 

 

 

 

 

 

 

 

Options expired (vested)

 

 

(79

)

 

 

30.61

 

 

 

 

 

 

 

 

 

Balance at September 30, 2018

 

 

5,683

 

 

$

18.33

 

 

 

5.76

 

 

$

1,448

 

Vested and expected to vest at

  September 30, 2018

 

 

5,422

 

 

$

18.41

 

 

 

5.72

 

 

$

1,419

 

Exercisable at September 30, 2018

 

 

2,766

 

 

$

20.01

 

 

 

5.14

 

 

$

927

 

 

Summary of Restricted Stock Units Activity

Restricted stock unit activity under our stock-based compensation plans during the nine months ended September 30, 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

 

452

 

 

 

16.04

 

Vested

 

(1,049

)

 

 

5.91

 

Forfeited

 

(51

)

 

 

7.79

 

Non-vested as of September 30, 2018

 

1,795

 

 

$

8.54

 

 

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

 

 

Nine Months Ended

 

 

Nine Months Ended

 

 

September 30,

 

 

September 30,

 

 

September 30,

 

 

2018

 

 

2017

 

 

2018

 

 

2017

 

 

2018

 

 

2017

 

Weighted-average fair value

$

9.36

 

 

$

8.11

 

 

$

10.91

 

 

$

4.73

 

 

$

8.30

 

 

$

3.05

 

Risk-free interest rate

 

2.8

%

 

 

1.9

%

 

 

2.6

%

 

 

1.9

%

 

 

2.4

%

 

 

1.0

%

Expected life (in years)

 

4.5

 

 

 

4.5

 

 

 

4.5

 

 

 

4.5

 

 

 

1.3

 

 

 

1.2

 

Volatility

 

0.9

 

 

 

0.9

 

 

 

0.9

 

 

 

0.9

 

 

 

1.1

 

 

 

1.0

 

 

Stock-Based Compensation Expense

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

 

Three Months Ended

 

 

Nine Months Ended

 

 

September 30,

 

 

September 30,

 

 

2018

 

 

2017

 

 

2018

 

 

2017

 

Research and development

$

2,332

 

 

$

1,973

 

 

$

7,194

 

 

$

5,707

 

Selling, general and administrative

 

2,976

 

 

 

1,687

 

 

 

8,561

 

 

 

5,137

 

Cost of sales - product

 

443

 

 

 

-

 

 

 

1,085

 

 

 

-

 

Inventory

 

295

 

 

 

-

 

 

 

295

 

 

 

-

 

Total

$

6,046

 

 

$

3,660

 

 

$

17,135

 

 

$

10,844