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Stockholders' Equity Stockholders' Equity (Assumptions using the Black-Scholes option pricing model) (Details) - Employee Stock Option
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected dividend yield 1.18% 0.75% 0.50%
Expected volatility 27.08% 29.29% 31.21%
Risk-free interest rate 2.65% 1.95% 1.23%
Expected life (years) 5 years 5 years 5 years