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Note 13 - Equity Incentive Plan - Assumptions Used to Estimate Fair Value of Stock Options and Stock Appreciation Rights (Details)
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Expected life (years) (Year) 3 years 182 days   4 years
Expected dividend yield 0.00% 0.00% 0.00%
Minimum [Member]      
Risk free interest rate 1.41% 2.15% 1.60%
Expected volatility 44.27% 37.12% 38.74%
Expected life (years) (Year)   4 years  
Maximum [Member]      
Risk free interest rate 2.54% 2.82% 1.86%
Expected volatility 48.52% 45.61% 44.31%
Expected life (years) (Year)   4 years 182 days