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Stock Incentive Plan (Weighted Average Grant-Date Fair Value Of SSARS And Assumptions Under Black-Scholes Option Model) (Details) - Stock Appreciation Rights (SARs) - $ / shares
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Weighted average grant date fair value (in dollars per share) $ 12.31 $ 11.34 $ 12.88
Expected life of awards (years) 3 years 3 years 3 years
Risk-free interest rate 1.50% 2.60% 2.20%
Expected volatility 24.10% 24.20% 23.70%
Expected dividend yield 0.90% 1.00% 0.80%