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Equity Plans and Stock-Based Compensation (Tables)
9 Months Ended
Sep. 30, 2024
Share-Based Payment Arrangement [Abstract]  
Option Activity under Stock-Based Compensation Plans
The following table summarizes the activity of stock options for the nine months ended September 30, 2024:
 
Shares
Underlying
Outstanding
Options
(in thousands)
Weighted-
Average
Exercise
Price Per Share
Weighted-
Average
Remaining
Contractual
Term (years)
Aggregate
Intrinsic
Value (in thousands)
Balance as of December 31, 202310,120$10.78 4.18$37,388 
Options granted1,71012.37 
Options exercised(537)7.76 
Options cancelled:
Options forfeited (unvested)(22)11.56 
Options expired (vested)(144)14.63 
Balance as of September 30, 202411,127$11.12 3.98$13,791 
Vested and expected to vest as of September 30, 202410,939$11.10 3.95$13,788 
Exercisable as of September 30, 20248,268$10.79 3.32$13,693 
Summary of Restricted Stock Units Activity
The following table summarizes the activity of RSUs for the nine months ended September 30, 2024:
 
Number of Shares
(in thousands)
Weighted-Average
Grant-Date Fair
Value Per Share
Non-vested as of December 31, 20234,445$11.57 
Granted3,13912.42 
Vested (1)
(1,815)11.14 
Forfeited(257)12.38 
Non-vested as of September 30, 20245,512$12.16 
(1)Inclusive of approximately 699,684 RSUs for the nine months ended September 30, 2024, which were not converted into shares due to net share settlement in order to cover the required amount of employee withholding taxes. The value of the withheld shares was classified as a reduction to additional paid-in capital.
Summary of Performance Based Restricted Stock Unit
We granted market-based performance restricted stock units (“PSUs”) to certain executives. These PSUs vest upon a specified market condition. The summary of PSU activities for the nine months ended September 30, 2024 is as follows:
 
Number of Shares
(in thousands)
Weighted-Average
Grant-Date Fair
Value Per Share
Non-vested as of December 31, 2023557$15.95 
Granted55817.23 
Non-vested as of September 30, 20241,115$16.59 
Fair Value-Based Measurements and Weighted-Average Assumptions The weighted-average assumptions used in the calculations of these fair value measurements are as follows:
Stock Options
Stock Options
Market-Based Performance Stock Units
Three Months Ended
September 30,
Nine Months Ended
September 30,
Nine Months Ended
September 30,
202420232024202320242023
Weighted-average fair value per share$6.66 $8.61 $7.82 $7.30 $17.23 $18.25 
Risk-free interest rate3.8 %4.2 %4.2 %4.0 %4.3 %4.3 %
Expected life (in years)4.54.54.54.52.92.9
Volatility0.80.80.80.80.60.9
Stock-Based Compensation Expense
The following table summarizes stock-based compensation expense recorded in each component of operating expenses in our condensed consolidated statements of operations, and amounts capitalized to our inventories (in thousands):
Three Months Ended
September 30,
Nine Months Ended
September 30,
2024202320242023
Research and development$3,135 $2,339 $8,681 $6,752 
Selling, general and administrative8,703 7,320 26,878 21,353 
Cost of sales - product397 369 1,505 1,463 
Inventories848 659 2,551 1,715 
Total$13,083 $10,687 $39,615 $31,283