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Stock-based Compensation Expense (Tables)
3 Months Ended
Mar. 31, 2024
Stock-based Compensation Expense [Abstract]  
Stock-Based Compensation Expense

The following table summarizes stock-based compensation expense for the three months ended March 31, 2024 and 2023 (in thousands):


 
Three Months Ended
March 31,
 
   
2024
   
2023
 
Cost of sales
 
$
204
   
$
119
 
Research, development and patent expense
   
22,225
     
19,567
 
Selling, general and administrative expense
   
8,911
     
7,262
 
Total
 
$
31,340
   
$
26,948
 
Weighted-Average Assumptions for Stock Options

Employee Stock Options:
 
Three Months Ended
March 31,
 
   
2024
   
2023
 
Risk-free interest rate
   
4.0
%
   
3.6
%
Dividend yield
   
0.0
%
   
0.0
%
Volatility
   
44.0
%
   
47.5
%
Expected life
 
6.3 years
   
6.3 years
 
Weighted-Average Assumptions for ESPP

ESPP:
 
Three Months Ended
March 31,
 
   
2024
   
2023
 
Risk-free interest rate
   
5.3
%
   
5.2
%
Dividend yield
   
0.0
%
   
0.0
%
Volatility
   
38.4
%
   
36.7
%
Expected life
 
6 months
   
6 months