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Stock Based Compensation (Narrative) (Details) - USD ($)
shares in Millions, $ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of shares authorized 15.0    
Grants in period 0.7 0.8 0.8
Risk free interest rate   2.55%  
Expected dividend rate   5.60% 5.60%
Equity based compensation, noncash expense $ 11.9 $ 13.6 $ 9.4
Equity based compensation, amount capitalized (0.9) $ (0.9) $ 0.0
Compensation cost not yet recognized $ 13.7    
Weighted average remaining contractual term 2 years    
Minimum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Service period 1 year    
Expected volatility rate 20.00% 20.00% 29.00%
Risk free interest rate 1.20%   2.43%
Expected dividend rate 5.90%    
Maximum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Service period 5 years    
Expected volatility rate 23.00% 21.00% 32.00%
Risk free interest rate 1.30%   2.53%
Expected dividend rate 6.00%