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Stock-Based Compensation (Tables)
12 Months Ended
Dec. 31, 2021
Stock-Based Compensation  
Schedule of total employee, director and non-employee stock-based compensation expense recognized

Year Ended

 

December 31, 

 

(in thousands)

2021

2020

2019

 

General and administrative

    

$

12,813

    

$

10,769

    

$

8,854

Research and development

24,162

20,850

 

22,997

$

36,975

$

31,619

$

31,851

Year Ended

December 31, 

(in thousands)

2021

2020

2019

Stock options

    

$

27,909

    

$

26,045

    

$

30,502

ESPP

992

 

804

 

687

RSUs

8,074

 

4,770

 

662

$

36,975

$

31,619

$

31,851

Schedule of stock options outstanding

    

December 31, 

 

2021

2020

2019

 

Exercisable options

 

5,576,430

 

4,668,179

 

3,950,965

Weighted average exercise price per share of exercisable options

$

24.15

$

21.75

$

17.79

Weighted average grant date fair value per share of options granted during the year

$

21.65

$

16.96

$

20.74

Options available for future grants

 

3,597,371

 

3,346,092

 

3,975,160

Weighted average remaining contractual life

 

6.65

 

7.00

 

7.32

Summary of stock option activity

    

    

    

Weighted-

    

 

Weighted-

Average

 

Average

Remaining

 

Exercise

Contractual

Aggregate

 

Number of

Price

Term

Intrinsic Value

 

Shares

(Per Share)(1)

(in years)

(in thousands)(2)

 

Balances at December 31, 2019

 

7,174,319

 

24.03

 

7.32

$

79,116

Options granted

 

1,679,324

33.08

Options forfeited

 

(243,384)

32.93

Options exercised(3)

 

(858,470)

19.36

Balances at December 31, 2020

 

7,751,789

 

26.23

 

7.00

$

134,941

Options granted

 

1,827,234

41.22

Options forfeited

 

(382,454)

36.15

Options exercised(3)

 

(520,240)

23.61

Balances at December 31, 2021

 

8,676,329

$

29.11

6.65

$

100,057

As of December 31, 2021

Options vested and expected to vest

 

8,676,329

$

29.11

 

6.65

$

100,057

Exercisable

 

5,576,430

$

24.15

 

5.53

$

89,287

Schedule of stock options outstanding and exercisable by exercise price

Stock Options Outstanding

Stock Options Exercisable

 

Weighted-

 

Average

 

    

    

Remaining

    

Weighted-

    

    

Weighted-

 

Range of

Contractual

Average

Average

 

Exercise

Number of

Term

Exercise Price

Number of

Exercise Price

 

Prices

Shares

(in years)

Per Share

Shares

Per Share

 

$4.25 – $10.28

 

151,488

 

1.68

$

4.29

 

151,488

$

4.29

$10.52 – $15.78

 

1,508,709

 

3.33

$

13.15

 

1,507,724

$

13.15

$15.91 – $23.87

 

1,777,216

 

5.52

$

22.77

 

1,756,016

$

22.76

$23.96 – $35.94

2,312,270

7.91

$

32.08

1,168,530

$

31.65

$35.99 – $53.99

2,926,646

8.31

$

40.12

992,672

$

37.52

 

8,676,329

 

6.65

$

29.11

 

5,576,430

$

24.15

Schedule of weighted average assumptions used for estimation of fair value of stock options

Options

    

2021

    

2020

    

2019

 

Common stock fair value per share

$

30.65 - 49.47

$

20.69 - 45.91

$

29.96 - 44.19

Expected volatility

 

53.91% - 56.82%

 

52.93% - 58.95%

 

60.67% - 61.33%

Risk-free interest rate

 

0.47% - 1.33%

 

0.29% - 1.71%

 

1.37% - 2.60%

Expected dividend yield

 

 

 

Expected term (in years)

 

6.00 - 7.65

 

5.23 - 7.65

 

5.23 - 6.59

Schedule of weighted average assumptions used for estimation of fair value of ESPP

ESPP

    

2021

    

2020

    

2019

Expected term (years)

 

0.5 - 2.0

 

0.5 - 2.0

 

0.5 - 2.0

Expected volatility

46.08% - 66.37%

50.77% - 66.37%

50.77% - 71.37%

Risk-free interest rate

 

0.04% - 1.65%

0.09% - 1.65%

1.47% - 2.70%

Expected dividend yield

Summary of restricted stock unity activity

Weighted-

Average

Grant Date

Number of

Fair Value

Shares

(Per Unit)

Unvested at December 31, 2019

 

90,006

$

34.66

Granted

 

348,288

32.51

Vested

 

(62,355)

32.61

Forfeited

(17,114)

32.33

Unvested at December 31, 2020

 

358,825

$

33.04

Granted

 

670,700

39.11

Vested

 

(151,555)

32.76

Forfeited

(51,822)

36.68

Unvested at December 31, 2021

 

826,148

$

37.79