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Note 10 - Common Stock and Stock-based Compensation Plans - Valuation Assumptions (Details) - The 2002 Employee Stock Purchase Plan [Member] - Purchase Rights [Member]
6 Months Ended
Jun. 30, 2022
Jun. 30, 2021
Expected dividend yield 0.00% 0.00%
Expected volatility 38.00%  
Expected volatility   39.00%
Expected volatility, maximum   56.00%
Risk-free interest rate 0.50%  
Risk-free interest rate, minimum   0.10%
Risk-free interest rate, Maximum   1.70%
Contractual term of up to (Month) 24 months 24 months