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Capital Stock and Dividend Restrictions - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions |  |  | 12 Months Ended |  |  |
--- | --- | --- | --- | --- | --- | ---
Dec. 14, 2023 | Feb. 01, 2022 | Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021 | May 25, 2023 | Mar. 24, 2022 | Dec. 14, 2021
Class of Stock |  |  |  |  |  |  |  |
Common stock, shares authorized |  |  | 150,000,000 |  |  |  | 250,000,000 |
Common stock, shares, outstanding |  |  | 103,941,626 | 104,442,023 |  |  |  |
Stock compensation expense |  |  | $ 4.7 | $ 9.6 | $ 8.9 |  |  |
Payments for Repurchase of Common Stock | $ 32.1 |  | $ 34.0 | $ 199.0 | $ 5.4 |  |  |
Stock Repurchased and Retired During Period, Shares |  |  | 1,056,191 | 5,040,896 | 128,171 |  |  |
Sale of Stock Shares Authorized For Future Sale |  |  |  |  |  |  |  | 47,158,390
Preferred Stock, Shares Authorized |  |  | 100,000 | 100,000 |  |  |  |
Capital Stock, Authorized |  |  | 150,100,000 |  |  |  |  |
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Authorized |  |  |  |  |  | 2,000,000,000,000 |  |
Great Western Bank |  |  |  |  |  |  |  |
Class of Stock |  |  |  |  |  |  |  |
Total consideration paid |  | $ 1,723.3 |  |  |  |  |  |
Class A Common Stock |  |  |  |  |  |  |  |
Class of Stock |  |  |  |  |  |  |  |
Stock Repurchased and Retired During Period, Shares |  |  |  | 5,000,000,000,000 |  |  |  |
Class A Common Stock |  |  |  |  |  |  |  |
Class of Stock |  |  |  |  |  |  |  |
Common stock, shares authorized |  |  |  |  |  |  | 150,000,000 |
Common Stock, Voting Rights, Votes Per Share |  |  | $ 1 |  |  |  |  |
Common stock, shares, outstanding |  |  |  | 104,442,023 |  |  |  |
Class A Common Stock | Great Western Bank |  |  |  |  |  |  |  |
Class of Stock |  |  |  |  |  |  |  |
Common stock issued (in shares) |  | 46,879,601 |  |  |  |  |  |
Class B Common Stock |  |  |  |  |  |  |  |
Class of Stock |  |  |  |  |  |  |  |
Common stock, shares authorized |  |  |  |  |  |  | 100,000,000 |
Director [Member] | Class A Common Stock |  |  |  |  |  |  |  |
Class of Stock |  |  |  |  |  |  |  |
Shares issued to directors during period |  |  | 54,414 |  |  |  |  |
Stock compensation expense |  |  | $ 1.2 |  |  |  |  |
Board of Directors |  |  |  |  |  |  |  |
Class of Stock |  |  |  |  |  |  |  |
Aggregate value of shares issued to directors |  |  |  | $ 1.3 |  |  |  |
Board of Directors | Class A Common Stock |  |  |  |  |  |  |  |
Class of Stock |  |  |  |  |  |  |  |
Shares issued to directors during period |  |  |  | 33,769 |  |  |  |

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