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Share-Based Payment Arrangements (Narrative) (Details)
$ / shares in Units, $ in Millions
9 Months Ended
Sep. 30, 2017
USD ($)
entity
$ / shares
shares
Sep. 30, 2016
USD ($)
Options [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Intrinsic value of options exercised | $ $ 4.1  
Restricted and Performance Shares [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Total unrecognized compensation expense | $ $ 40.1  
Weighted-average period 3 years  
Total fair value of shares vested | $ $ 10.1 $ 2.2
Shares granted | shares 63,127  
Grant date fair value per share | $ / shares $ 42.16  
Executive Management [Member] | Performance Shares [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Service period 3 years  
Executive Management [Member] | Performance Shares [Member] | Total Shareholder Return [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Shares granted | shares 23,489  
Grant date fair value per share | $ / shares $ 42.92  
Vesting performance period 3 years  
Number of peer group regional banks | entity 44  
Executive Management [Member] | Performance Shares [Member] | Core Earnings Per Share [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Shares granted | shares 23,489  
Grant date fair value per share | $ / shares $ 38.26  
Vesting performance period 2 years  
Executive Management [Member] | Tranche One [Member] | Performance Shares [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Percentage of maximum number of shares vested 200.00%