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Equity-based Compensation (Tables)
12 Months Ended
Dec. 31, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]  
Schedule of Stock-Based Compensation Expense Stock‑based compensation expense by classification within the consolidated statements of operations and comprehensive income (loss) is as follows (in thousands):

 

 

 

Years Ended December 31,

 

 

 

2020

 

 

2019

 

 

2018

 

Research and development

 

$

35,120

 

 

$

23,273

 

 

$

17,557

 

General and administrative

 

 

30,898

 

 

 

20,784

 

 

 

17,428

 

Loss from equity method investment

 

 

 

 

 

5,467

 

 

 

4,275

 

Total

 

$

66,018

 

 

$

49,524

 

 

$

39,260

 

 

Fair Value of Each Option Issued to Employees and Non-employees Estimated Using Black-Scholes Option-Pricing Model

The fair value of each option issued to employees and non-employees was estimated at the date of grant using the Black-Scholes option pricing model with the following weighted-average assumptions:

 

 

 

Years Ended December 31,

 

 

 

2020

 

 

2019

 

 

2018

 

Options granted

 

 

2,182,773

 

 

 

2,832,784

 

 

 

2,209,597

 

Weighted-average exercise price

 

$

68.91

 

 

$

39.16

 

 

$

51.73

 

Weighted-average grant date fair value

 

$

42.28

 

 

$

24.57

 

 

$

33.82

 

Assumptions:

 

 

 

 

 

 

 

 

 

 

 

 

Expected volatility

 

 

69.2

%

 

 

68.9

%

 

 

71.9

%

Expected term (in years)

 

 

6.0

 

 

 

6.0

 

 

 

6.0

 

Risk-free interest rate

 

 

0.6

%

 

 

2.2

%

 

 

2.8

%

Expected dividend yield

 

 

0.0

%

 

 

0.0

%

 

 

0.0

%

 

Summary of Stock Option Activity

The following table summarizes stock option activity under the Company’s equity award plans (intrinsic value in thousands):

 

 

 

Shares

 

 

Weighted-

Average

Exercise Price

 

 

Weighted-

Average

Remaining

Contractual

Term (years)

 

 

Aggregate

Intrinsic

Value

 

Outstanding at December 31, 2019

 

 

7,782,437

 

 

$

31.30

 

 

 

8.2

 

 

$

231,554

 

Granted

 

 

2,182,773

 

 

$

68.91

 

 

 

 

 

 

 

 

 

Exercised

 

 

(1,517,735

)

 

$

23.53

 

 

 

 

 

 

 

 

 

Cancelled or forfeited

 

 

(345,495

)

 

$

41.61

 

 

 

 

 

 

 

 

 

Outstanding at December 31, 2020

 

 

8,101,980

 

 

$

42.44

 

 

 

7.8

 

 

 

896,666

 

Exercisable at December 31, 2020

 

 

3,838,372

 

 

$

30.43

 

 

 

7.0

 

 

$

470,907

 

Vested and expected to vest at

   December 31, 2020

 

 

8,101,980

 

 

$

42.44

 

 

 

7.8

 

 

$

896,666

 

 

 

Summary of Restricted Stock Activity

The following table summarizes the restricted stock activity under the Company’s equity award plans:

 

 

 

Shares

 

 

Weighted-

Average

Grant Date

Fair Value

 

Unvested balance at December 31, 2019

 

 

699,534

 

 

$

56.53

 

Granted

 

 

437,670

 

 

 

77.92

 

Vested

 

 

(204,650

)

 

 

42.92

 

Cancelled or forfeited

 

 

(38,462

)

 

 

46.33

 

Unvested balance at December 31, 2020

 

 

894,092

 

 

$

70.55