Shareholders' Equity (Details) - USD ($) $ / shares in Units, $ in Thousands			1 Months Ended	3 Months Ended	9 Months Ended
	May 19, 2020	Feb. 21, 2019	Mar. 31, 2019	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 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				$ 55,500	$ 56,500	$ 180,400
Treasury stock acquired, Shares,				1,000,000.0	1,100,000	3,300,000
Treasury Stock Acquired, Average Cost Per Share				$ 55.43	$ 49.62	$ 55.10
Stock Repurchase Program, Authorized Amount					$ 0
Preferred stock, par value				$ 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	$ 225,000
Preferred stock, dividend rate percentage	6.125%
Preferred stock, par value	$ 1.00
Preferred stock liquidation preference per depositary share	25
Preferred stock, liquidation preference per share	$ 25,000
Series C Preferred Stock [Member] | Over-Allotment Option [Member]
Business Acquisition Equity Interests Issued Or Issuable [Line Items]
Issuance of preferred stock	$ 25,000
Non-Cumulative Perpetual Preferred Stock, Series B [Member]
Business Acquisition Equity Interests Issued Or Issuable [Line Items]
Issuance of preferred stock		$ 150,000
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
Series B Preferred Stock [Member] | Over-Allotment Option [Member]
Business Acquisition Equity Interests Issued Or Issuable [Line Items]
Issuance of preferred stock			$ 10,000
Business Bancshares, Inc. [Member]
Business Acquisition Equity Interests Issued Or Issuable [Line Items]
Issuance of common stock					1,400,000