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Equity and Stock-based Compensation (Tables)
 12 Months Ended
Dec. 31, 2023
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,

 

 

 

2023

 

 

2022

 

Common stock outstanding

 

 

98,770

 

 

 

94,166

 

Stock options outstanding

 

 

11,104

 

 

 

9,088

 

RSUs outstanding

 

 

4,404

 

 

 

3,669

 

Shares reserved for future stock options and RSUs grant

 

 

10,769

 

 

 

11,524

 

Shares reserved for future ESPP offering

 

 

5,952

 

 

 

5,373

 

Total shares of common stock reserved

 

 

130,999

 

 

 

123,820

 
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, 2022

 

 

9,088

 

 

$

29.19

 

 

 

 

 

 

 

Granted

 

 

5,738

 

 

 

7.27

 

 

 

 

 

 

 

Exercised

 

 

(122

)

 

 

12.42

 

 

 

 

 

 

 

Forfeited

 

 

(1,725

)

 

 

22.49

 

 

 

 

 

 

 

Expired

 

 

(1,875

)

 

 

34.38

 

 

 

 

 

 

 

Outstanding at December 31, 2023

 

 

11,104

 

 

 

18.21

 

 

 

7.26

 

 

$

83

 

Vested and expected to vest, December 31, 2023

 

 

10,224

 

 

 

19.21

 

 

 

7.11

 

 

 

68

 

Exercisable at December 31, 2023

 

 

4,688

 

 

$

30.66

 

 

 

5.04

 

 

$

—

 
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, 2022

 

 

3,669

 

 

$

18.80

 

Granted

 

 

4,612

 

 

 

11.61

 

Vested

 

 

(2,002

)

 

 

14.70

 

Forfeited

 

 

(1,875

)

 

 

20.58

 

Unvested at December 31, 2023

 

 

4,404

 

 

$

12.37

 
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, 2023, 2022 and 2021 was as follows (in thousands):

 

 

 

Years Ended December 31,

 

 

 

2023

 

 

2022

 

 

2021

 

Research and development

 

$

25,462

 

 

$

34,861

 

 

$

40,547

 

Selling, general and administrative

 

 

25,305

 

 

 

30,740

 

 

 

30,614

 

Total stock-based compensation expense

 

$

50,767

 

 

$

65,601

 

 

$

71,161

 
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,

 

 

 

 

2023

 

 

 

2022

 

 

 

2021

 

 

Stock Options

 

 

 

 

 

 

 

 

 

 

 

 

Expected term (in years)

 

 

6.1

 

 

 

 

5.7

 

 

 

 

5.7

 

 

Expected volatility

 

 

92.8

 

%

 

 

66.8

 

%

 

 

61.9

 

%

Risk-free interest rate

 

 

3.0

 

%

 

 

2.2

 

%

 

 

0.8

 

%

Expected dividend yield

 

 

—

 

 

 

 

—

 

 

 

 

—

 

 

Weighted average estimated fair value

 

$

4.67

 

 

 

$

7.88

 

 

 

$

20.21

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

ESPPs

 

 

 

 

 

 

 

 

 

 

 

 

Expected term (in years)

 

0.5 - 2.0

 

 

 

0.5 - 2.0

 

 

 

0.5 - 2.0

 

 

Expected volatility

 

56.7 - 271.2

 

%

 

58.5 - 97.6

 

%

 

47.1 - 104.4

 

%

Risk-free interest rate

 

0.2 - 5.2

 

%

 

0.1 - 4.5

 

%

 

0.0 - 2.2

 

%

Expected dividend yield

 

 

—

 

 

 

 

—

 

 

 

 

—

 

 

Weighted average estimated fair value

 

$

5.64

 

 

 

$

8.60

 

 

 

$

12.40

 

 

 
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,

 

 

 

 

2023

 

 

 

2022

 

 

TSR awards

 

 

 

 

 

 

 

 

Expected term (in years)

 

 

3.9

 

 

 

 

3.9

 

 

Expected volatility

 

69.0 - 73.3

 

%

 

 

69.0

 

%

Risk-free interest rate

 

1.8 - 4.2

 

%

 

 

1.8

 

%

Expected dividend yield

 

 

—

 

 

 

 

—

 

 

Weighted average estimated fair value

 

$

28.90

 

 

 

$

24.01