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Share-Based Compensation (Share-Based Compensation Valuation Assumptions) (Details) - Stock Options [Member] - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock option expense for the year $ 4,950 $ 17,162 $ 8,707
Aggregate exercise date intrinsic value of options exercised during the year $ 11,848 $ 25,117 $ 61,334
Expected life of options in years, based upon historical experience 5 years 5 years 5 years
Risk-free interest rate 2.30% 2.70% 1.90%
Expected volatility, based upon historical volatility 8.90% 12.50% 17.90%
Expected dividend yield 3.60% 4.10% 3.60%
Average estimated value of options granted during the year $ 9.61 $ 13.09 $ 23.49
Acceleration of amortization on grants   $ 8,100  
Reduction in compensation expense resulting from forfeitures     $ 800