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Note 3 - Stock-based Compensation and Shareholders' Equity (Details) - Assumptions Used in Option Pricing Model
9 Months Ended
Sep. 30, 2015
Sep. 30, 2014
Assumptions Used in Option Pricing Model [Abstract]    
Risk free interest rate 1.06% 0.69%
Dividend yield 3.86% 4.28%
Volatility 26.74% 28.12%
Expected life (years) 5 years 5 years