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Note 1 - Assumptions Used in Option Pricing Model (Details)
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Assumptions Utilized for Stock Option Grants [Abstract]      
Risk free interest rate 1.14% 1.06% 0.69%
Dividend yield 3.78% 3.86% 4.28%
Volatility 22.60% 26.70% 28.10%
Expected life (years) 4 years 2 months 12 days 5 years 5 years