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Equity and Stock-based Compensation (Tables)
12 Months Ended
Dec. 31, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]  
Summary of Common Stock Reserved for Future Issuance

Shares of Common Stock outstanding, shares of stock plans outstanding and shares reserved for future issuance related to stock options and RSU grants and the Company’s Employee Stock Purchase Plan (“ESPP”) purchases are as follows (in thousands):

 

 

 

December 31,

 

 

 

2019

 

 

2018

 

Common stock outstanding

 

 

87,657

 

 

 

85,432

 

Stock options outstanding

 

 

10,018

 

 

 

10,430

 

RSUs outstanding

 

 

1,483

 

 

 

1,428

 

Common stock warrants outstanding

 

 

 

 

 

4

 

Shares reserved for future stock options and RSUs grant

 

 

7,725

 

 

 

6,041

 

Shares reserved for future ESPP offering

 

 

3,337

 

 

 

2,618

 

Total shares of common stock reserved

 

 

110,220

 

 

 

105,953

 

 

Summary of Stock Option Transactions

Stock option transactions, including forfeited options granted under the 2014 Plan as well as prior plans, are summarized below:

 

 

 

Shares

(In thousands)

 

 

Weighted

Average

Exercise per

Share

 

 

Weighted

Average

Remaining Contractual

Life

(In Years)

 

 

Aggregate

Intrinsic Value

(In thousands)

 

Outstanding at December 31, 2018

 

 

10,430

 

 

$

20.25

 

 

 

 

 

 

 

 

 

Granted

 

 

1,909

 

 

 

53.75

 

 

 

 

 

 

 

 

 

Exercised

 

 

(1,642

)

 

 

10.15

 

 

 

 

 

 

 

 

 

Expired

 

 

(21

)

 

 

50.40

 

 

 

 

 

 

 

 

 

Forfeited

 

 

(658

)

 

 

44.65

 

 

 

 

 

 

 

 

 

Outstanding at December 31, 2019

 

 

10,018

 

 

 

26.63

 

 

 

5.17

 

 

$

193,226

 

Vested and expected to vest, December 31, 2019

 

 

10,018

 

 

 

26.63

 

 

 

5.17

 

 

 

193,226

 

Exercisable at December 31, 2019

 

 

7,318

 

 

$

18.63

 

 

 

3.89

 

 

$

183,707

 

Summary of RSU Activity

The following table summarizes RSU activity:

 

 

Shares

(In thousands)

 

 

Fair Value at Grant

 

Unvested at December 31, 2018

 

 

1,428

 

 

$

38.26

 

Granted

 

 

1,110

 

 

 

54.74

 

Vested

 

 

(715

)

 

 

37.71

 

Forfeited

 

 

(340

)

 

 

46.15

 

Unvested at December 31, 2019

 

 

1,483

 

 

$

49.05

 

 

Schedule of Allocated Stock-Based Compensation Expense

Stock-based compensation expense allocated to research and development and selling, general and administrative expense for the years ended December 31, 2019, 2018 and 2017 was as follows (in thousands):

 

 

 

Years Ended December 31,

 

 

 

2019

 

 

2018

 

 

2017

 

Research and development

 

$

41,015

 

 

$

30,491

 

 

$

21,807

 

Selling, general and administrative

 

 

25,252

 

 

 

21,651

 

 

 

15,732

 

Total stock-based compensation expense

 

$

66,267

 

 

$

52,142

 

 

$

37,539

 

 

Schedule of Assumptions used to Estimate Fair Value of Stock Options Granted and Employee Stock Purchase Plans

The assumptions used to estimate the fair value of stock options granted and ESPPs using the Black-Scholes option valuation model were as follows:

 

 

 

Years Ended December 31,

 

 

2019

 

 

 

2018

 

 

 

2017

 

 

Stock Options

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Expected term (in years)

 

 

5.3

 

 

 

 

5.4

 

 

 

 

5.7

 

 

Expected volatility

 

 

68.0

 

%

 

 

67.9

 

%

 

 

71.5

 

%

Risk-free interest rate

 

 

2.4

 

%

 

 

2.7

 

%

 

 

2.2

 

%

Expected dividend yield

 

 

 

 

 

 

 

 

 

 

 

 

Weighted average estimated fair value

 

$

31.98

 

 

 

$

32.12

 

 

 

$

16.96

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

ESPPs

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Expected term (in years)

 

0.5 - 2.0

 

 

 

0.5 - 2.0

 

 

 

0.5 - 2.0

 

 

Expected volatility

 

48.1 - 62.1

 

%

 

47.3 - 75.3

 

%

 

52.8 - 77.2

 

%

Risk-free interest rate

 

1.3 - 2.9

 

%

 

0.8 - 2.9

 

%

 

0.5 - 1.6

 

%

Expected dividend yield

 

 

 

 

 

 

 

 

 

 

 

 

Weighted average estimated fair value

 

$

19.27

 

 

 

$

16.27

 

 

 

$

9.41