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Shareholders' Equity (Details) - USD ($)
$ / shares in Units, $ in Millions
 1 Months Ended 3 Months Ended
Feb. 21, 2019
Mar. 31, 2019
Mar. 31, 2020
Mar. 31, 2019
Dec. 31, 2019
Business Acquisition Equity Interests Issued Or Issuable [Line Items]          
Number of shares authorized to be repurchased     8,900,000    
Purchase of treasury stock     $ 56.2 $ 53.9  
Treasury stock acquired, Shares,     1,100,000 1,000,000.0  
Treasury Stock Acquired, Average Cost Per Share     $ 49.74 $ 53.25  
Preferred stock, par value   $ 1.00 $ 1 $ 1.00 $ 1
Non-Cumulative Perpetual Preferred Stock, Series B [Member]          
Business Acquisition Equity Interests Issued Or Issuable [Line Items]          
Issuance of preferred stock $ 150.0        
Preferred stock, dividend rate percentage 6.25%        
Preferred stock, par value $ 1.00        
Preferred stock liquidation preference per depositary share 25        
Preferred stock, liquidation preference per share $ 25,000        
Preferred stock, redemption terms     The Company may redeem the Series B preferred stock at its option, subject to regulatory approval, on or after March 15, 2024 or following a regulatory capital treatment event, as defined    
Series B Preferred Stock [Member] | Over-Allotment Option [Member]          
Business Acquisition Equity Interests Issued Or Issuable [Line Items]          
Issuance of preferred stock   $ 10.0      
Business Bancshares, Inc. [Member]          
Business Acquisition Equity Interests Issued Or Issuable [Line Items]          
Shares issued     1,300,000