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Note 10 - Stockholders' Equity and Stock-based Compensation - Fair Value Assumptions, Stock Options (Details)
12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Dividend yield 0.00% 0.00% 0.00%
Minimum [Member]      
Expected term (in years) (Year) 5 years 2 months 12 days 4 years 6 months 4 years 4 months 24 days
Volatility 38.00% 38.00% 40.00%
Risk-free interest rate 0.50% 0.30% 1.50%
Maximum [Member]      
Expected term (in years) (Year) 5 years 6 months 5 years 6 months 6 years 7 months 6 days
Volatility 41.00% 43.00% 46.00%
Risk-free interest rate 1.20% 1.40% 2.40%