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Stock-based Compensation
9 Months Ended
Sep. 30, 2023
Stock-based Compensation  
Stock-based Compensation

15. Stock-based Compensation

Performance Share Units

The Company periodically grants PSUs to certain members of the Company's senior management team. PSUs vest subject to the satisfaction of annual and cumulative performance and/or market conditions established by the Company’s Compensation Committee.

A summary of the Company’s PSU activity for the nine months ended September 30, 2023 and related information is as follows:

Weighted-Average

Shares

Grant Date Fair Value

Outstanding as of December 31, 2022

447,770

$

28.71

Granted

216,500

38.71

Vested

(223,170)

27.99

Forfeited

Performance adjustment

62,780

27.14

Outstanding as of September 30, 2023

503,880

$

33.13

The number of PSUs granted represents the target number of shares of common stock that may be earned. However, the actual number of shares earned may vary based on the satisfaction of performance criteria. The weighted-average grant date fair value of PSUs granted for the nine months ended September 30, 2023, and 2022 was $38.71 and $24.12, respectively.

Restricted Stock Units

The Company granted RSUs to employees during the nine months ended September 30, 2023. The Company’s RSUs generally vest ratably over a four-year period of service. A summary of the Company’s RSU activity for the nine months ended September 30, 2023 and related information is as follows:

Weighted-Average

Shares

Grant Date Fair Value

Outstanding as of December 31, 2022

2,047,571

$

19.67

Granted

1,268,907

26.27

Vested

(644,746)

19.90

Forfeited

(179,711)

21.85

Outstanding as of September 30, 2023

2,492,021

$

22.81

The weighted-average grant date fair value per share of RSUs granted for the nine months ended September 30, 2023 and 2022 was $26.27 and $17.48, respectively. The total fair value of RSUs vested (measured on the date of vesting) for the nine months ended September 30, 2023, and 2022 was $16,906 and $10,020, respectively.

Stock Options

A summary of the Company’s stock option activity for the nine months ended September 30, 2023 and related information is as follows:

 

 

 

Weighted-

 

 

Weighted-

 

Average

 

Average

 

Remaining

Aggregate

Exercise Price

 

Contractual

Intrinsic

    

Shares

    

per Share

    

Term (in years)

    

Value

Outstanding as of December 31, 2022

 

1,683,805

$

18.84

 

5.5

$

7,953

Exercised

 

(327,722)

16.43

Cancelled

 

(8,923)

18.87

Outstanding as of September 30, 2023

 

1,347,160

$

19.43

 

4.7

$

4,952

Exercisable as of September 30, 2023

 

1,310,344

$

19.38

4.6

$

4,910

There were no stock options granted during the nine months ended September 30, 2023 and 2022.

Employee Stock Purchase Plan

The Company’s 2015 Employee Stock Purchase Plan allows employees to purchase shares of the Company’s common stock. The purchase price is equal to 85% of the lower of the closing price of the Company’s common stock on (1) the first day of the purchase period or (2) the last day of the purchase period. During the nine months ended September 30, 2023, 26,505 shares of common stock were purchased for total proceeds of $460. The expense for the three months ended September 30, 2023 and 2022 was $55 and $28, respectively. The expense for the nine months ended September 30, 2023 and 2022 was $155 and $88, respectively.

Stock-based Compensation Expense

A summary of the allocation of the Company’s stock-based compensation expense for the three and nine months ended September 30, 2023 and 2022 is as follows:

Three Months Ended September 30,

Nine Months Ended September 30,

2023

2022

2023

2022

Research and development

$

    

$

$

    

$

1,591

Selling, general and administrative

 

7,027

5,377

 

20,134

15,613

Total stock-based compensation expense

$

7,027

$

5,377

$

20,134

$

17,204

As of September 30, 2023, there was approximately $50,041 of unrecognized compensation expense related to unvested options, restricted stock units and performance stock units, which is expected to be recognized as expense over a weighted average period of approximately 2.6 years.