Shareholders' Equity (Details) - USD ($) $ / shares in Units, $ in Millions					3 Months Ended		9 Months Ended
	Aug. 20, 2021	Jul. 22, 2021	Nov. 11, 2020	May 19, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Business Acquisition Equity Interests Issued Or Issuable [Line Items]
Number of shares authorized to be repurchased					11,900,000		11,900,000
Purchase of treasury stock					$ 44.8		$ 86.4	$ 56.5
Treasury stock acquired, Shares,					700,000	0	1,300,000	1,700,000
Treasury Stock Acquired, Average Cost Per Share					$ 66.74		$ 65.69	$ 33.08
Stock Dividend			50.00%
Preferred stock, par value					$ 1	$ 1.00	$ 1	$ 1.00	$ 1
Non-Cumulative Perpetual Preferred Stock, Series C [Member]
Business Acquisition Equity Interests Issued Or Issuable [Line Items]
Issuance of preferred stock				$ 225.0
Stock Dividend				6.125%
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 C preferred stock at its option, subject to regulatory approval, on or after June 15, 2025.
Series C Preferred Stock [Member] | Over-Allotment Option [Member]
Business Acquisition Equity Interests Issued Or Issuable [Line Items]
Issuance of preferred stock				$ 25.0
Non-cumulative Perpetual Series D Preferred Stock [Member]
Business Acquisition Equity Interests Issued Or Issuable [Line Items]
Stock Dividend		4.50%
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 D preferred stock at its option, subject to regulatory approval, on or after August 15, 2026.
Underwritten registered public offering		$ 300.0
Non-cumulative Perpetual Series A Preferred Stock [Member]
Business Acquisition Equity Interests Issued Or Issuable [Line Items]
Stock Dividend	6.25%
Preferred stock redemption price per depositary share	$ 25,000,000.00
Business Bancshares, Inc. [Member]
Business Acquisition Equity Interests Issued Or Issuable [Line Items]
Issuance of common stock							2,500,000