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Share Based Compensation Plans (Valuation Assumptions) (Details) - USD ($)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]      
Expected life of options granted 5 years 4 years 1 month 13 days 4 years 1 month 2 days
Risk-free interest rate 1.49% 1.25% 1.06%
Expected volatility of stock 29.00% 30.00% 30.00%
Annual expected dividend yield 3.00% 3.00% 3.00%
Fair value of granted options (in shares) $ 1,143,434 $ 473,272 $ 357,456
Nonvested options (in shares) 364,633 307,600 301,943