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Employee Benefit Plans (Performance Shares) (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]      
Weighted average period for compensation expense recognition 6 months    
Performance Shares      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Shares awarded (in shares) 374,900 316,100 401,200
Percentage of award paid in stock 50.00%    
Percentage of award paid in cash 50.00%    
Compensation expense $ 20.3 $ 16.8 $ 8.6
Total unrecognized compensation expense related to outstanding restricted stock units and restricted shares $ 19.0    
Weighted average period for compensation expense recognition 10 months 24 days    
Performance Shares | Minimum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Shares awarded after performance period, as a percentage of targeted amount 0.00%    
Performance Shares | Maximum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Shares awarded after performance period, as a percentage of targeted amount 150.00%    
Performance Shares Earned as Dividend Equivalents      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Shares awarded (in shares) 19,204 15,330 10,454
Executive Officer | Performance Shares      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Shares awarded (in shares) 168,627 116,872 168,786
Employees Other Than Named Executive Officers | Performance Shares      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Shares awarded (in shares) 187,036 183,908 221,958
Percentage of award paid in stock 100.00%