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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 |  |

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