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Stock-based Compensation
6 Months Ended
Jun. 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 six months ended June 30, 2023 and related information is as follows:

Weighted-Average

Shares

Grant Date Fair Value

Outstanding at 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 at June 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 six months ended June 30, 2023, and 2022 was $38.71 and $24.12, respectively.

Restricted Stock Units

The Company granted RSUs to employees during the six months ended June 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 six months ended June 30, 2023 and related information is as follows:

Weighted-Average

Shares

Grant Date Fair Value

Outstanding at December 31, 2022

2,047,571

$

19.67

Granted

1,248,207

26.33

Vested

(626,539)

20.03

Forfeited

(147,214)

21.62

Outstanding at June 30, 2023

2,522,025

$

22.76

The weighted-average grant date fair value per share of RSUs granted for the six months ended June 30, 2023 and 2022 was $26.33 and $17.48, respectively. The total fair value of RSUs vested (measured on the date of vesting) for the six months ended June 30, 2023, and 2022 was $16,480 and $9,697, respectively.

Stock Options

A summary of the Company’s stock option activity for the six months ended June 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 at December 31, 2022

 

1,683,805

$

18.84

 

5.5

$

7,953

Exercised

 

(306,537)

16.58

Cancelled

 

(8,300)

18.80

Outstanding at June 30, 2023

 

1,368,968

$

19.35

 

5.0

$

4,411

Exercisable at June 30, 2023

 

1,308,248

$

19.30

4.9

$

4,345

There were no stock options granted during the six months ended June 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 six months ended June 30, 2023, 11,329 shares of common stock were purchased for total proceeds of $169. The expense for the three months ended June 30, 2023 and 2022 was $55 and $28, respectively. The expense for the six months ended June 30, 2023 and 2022 was $101 and $60, respectively.

Stock-based Compensation Expense

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

Three Months Ended June 30,

Six Months Ended June 30,

2023

2022

2023

2022

Research and development

$

    

$

$

    

$

1,591

Selling, general and administrative

 

7,072

5,692

 

13,107

10,236

Total stock-based compensation expense

$

7,072

$

5,692

$

13,107

$

11,827

At June 30, 2023, there was approximately $57,292 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 2.8 years.