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Equity and Stock-based Compensation (Tables)
 12 Months Ended
Dec. 31, 2022
Share-Based Payment Arrangement [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,

 

 

 

2022

 

 

2021

 

Common stock outstanding

 

 

94,166

 

 

 

92,881

 

Stock options outstanding

 

 

9,088

 

 

 

8,967

 

RSUs outstanding

 

 

3,669

 

 

 

2,304

 

Shares reserved for future stock options and RSUs grant

 

 

11,524

 

 

 

10,253

 

Shares reserved for future ESPP offering

 

 

5,373

 

 

 

4,771

 

Total shares of common stock reserved

 

 

123,820

 

 

 

119,176

 

 
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 Price per
Share

 

 

Weighted
Average
Remaining Contractual
Life
(In Years)

 

 

Aggregate
Intrinsic Value
(In thousands)

 

Outstanding at December 31, 2021

 

 

8,967

 

 

$

34.84

 

 

 

 

 

 

 

Granted

 

 

2,902

 

 

 

14.72

 

 

 

 

 

 

 

Exercised

 

 

(179

)

 

 

8.24

 

 

 

 

 

 

 

Expired

 

 

(1,847

)

 

 

34.36

 

 

 

 

 

 

 

Forfeited

 

 

(755

)

 

 

32.89

 

 

 

 

 

 

 

Outstanding at December 31, 2022

 

 

9,088

 

 

 

29.19

 

 

 

7.03

 

 

$

6,232

 

Vested and expected to vest, December 31, 2022

 

 

8,614

 

 

 

29.61

 

 

 

6.93

 

 

 

5,770

 

Exercisable at December 31, 2022

 

 

4,730

 

 

$

35.07

 

 

 

5.45

 

 

$

1,438

 
Summary of RSU,PRSU and TSR Awards

The following table summarizes the activities of RSUs, PRSUs and TSR awards:

 

 

 

Shares
(In thousands)

 

 

Weighted Average Fair Value at Grant

 

Unvested at December 31, 2021

 

 

2,304

 

 

$

30.60

 

Granted

 

 

3,151

 

 

 

14.68

 

Vested

 

 

(1,142

)

 

 

27.72

 

Forfeited

 

 

(644

)

 

 

25.06

 

Unvested at December 31, 2022

 

 

3,669

 

 

$

18.80

 
Schedule of Recorded Stock-Based Compensation Expense

Stock-based compensation expense was recorded directly to research and development and selling, general and administrative expense for the years ended December 31, 2022, 2021 and 2020 was as follows (in thousands):

 

 

 

Years Ended December 31,

 

 

 

2022

 

 

2021

 

 

2020

 

Research and development

 

$

34,861

 

 

$

40,547

 

 

$

46,229

 

Selling, general and administrative

 

 

30,740

 

 

 

30,614

 

 

 

26,491

 

Total stock-based compensation expense

 

$

65,601

 

 

$

71,161

 

 

$

72,720

 
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,

 

 

2022

 

 

 

2021

 

 

 

2020

 

 

Stock Options

 

 

 

 

 

 

 

 

 

 

 

 

Expected term (in years)

 

 

5.7

 

 

 

 

5.7

 

 

 

 

5.7

 

 

Expected volatility

 

 

66.8

 

%

 

 

61.9

 

%

 

 

67.1

 

%

Risk-free interest rate

 

 

2.2

 

%

 

 

0.8

 

%

 

 

0.8

 

%

Expected dividend yield

 

 

—

 

 

 

 

—

 

 

 

 

—

 

 

Weighted average estimated fair value

 

$

7.88

 

 

 

$

20.21

 

 

 

$

18.36

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

ESPPs

 

 

 

 

 

 

 

 

 

 

 

 

Expected term (in years)

 

0.5 - 2.0

 

 

 

0.5 - 2.0

 

 

 

0.5 - 2.0

 

 

Expected volatility

 

58.5 - 97.6

 

%

 

47.1 - 104.4

 

%

 

47.5 - 77.1

 

%

Risk-free interest rate

 

0.1 - 4.5

 

%

 

0.0 - 2.2

 

%

 

0.1 - 2.9

 

%

Expected dividend yield

 

 

—

 

 

 

 

—

 

 

 

 

—

 

 

Weighted average estimated fair value

 

$

8.60

 

 

 

$

12.40

 

 

 

$

17.53

 

 

 
Schedule of Assumptions used to Estimate Fair Value of TSR Awards

The assumptions used to estimate the fair value of the TSR awards using the Monte Carlo valuation model were as follows:

 

 

 

Year Ended December 31,

 

 

 

 

2022

 

 

TSR awards

 

 

 

 

Expected term (in years)

 

 

3.9

 

 

Expected volatility

 

 

69.0

 

%

Risk-free interest rate

 

 

1.8

 

%

Expected dividend yield

 

 

—

 

 

Weighted average estimated fair value

 

$

24.01