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Stock Based Compensation (Narrative) (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Compensation expense and directors' fees related to stock awards $ 9.7 $ 9.5 $ 8.0
Compensation expense, non-vested awards $ 8.6 $ 7.7 $ 6.5
Number of shares issued to employees, directors and officers (in shares) 355,055    
Nonvested awards, total compensation cost not yet recognized $ 3.9    
Weighted Average      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Nonvested awards, total compensation cost not yet recognized, period for recognition 1 year    
Stock Awards | Independent directors      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Award vesting period 1 year