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Capital Stock and Dividend Restrictions - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions |  | 12 Months Ended |  |  |
--- | --- | --- | --- | --- | ---
Feb. 01, 2022 | Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020 | May 25, 2022 | Dec. 14, 2021 | Jun. 11, 2019
Class of Stock |  |  |  |  |  |  |
Common stock, shares authorized |  | 250,000,000 | 100,000,000 |  |  |  |
Common stock, shares, outstanding |  | 104,442,023 | 62,200,456 |  |  |  |
Stock compensation expense |  | $ 9.6 | $ 8.9 | $ 7.5 |  |  |
Aggregate purchase price of shares repurchased and retired |  | $ 199.0 | $ 5.4 | $ 116.8 |  |  |
Stock Repurchased and Retired During Period, Shares |  | 5,040,896 | 128,171 | 3,578,743 |  |  |
Sale of Stock Shares Authorized For Future Sale |  |  |  |  |  | 47,158,390 |
Accelerated Share Repurchases, Adjustment to Recorded Amount |  | $ 197.4 |  |  |  |  |
Treasury Stock Acquired, Average Cost Per Share |  | $ 39.48 |  |  |  |  |
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 |  |  |  |  |
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 |  |  | 41,699,409 |  |  |  |
Stock Repurchase Program, Number of Shares Authorized to be Repurchased |  |  |  |  |  |  | 5,000,000
Stock Repurchase Program, Remaining Number of Shares Authorized to be Repurchased |  |  |  |  | 1,889,158 |  |
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 |  |  |  |  |
Common stock, shares, outstanding |  | 0 | 20,501,047 |  |  |  |
Director [Member] | Class A Common Stock |  |  |  |  |  |  |
Class of Stock |  |  |  |  |  |  |
Shares issued to directors during period |  | 33,769 |  |  |  |  |
Stock compensation expense |  | $ 1.3 |  |  |  |  |
Board of Directors |  |  |  |  |  |  |
Class of Stock |  |  |  |  |  |  |
Aggregate value of shares issued to directors |  |  | $ 0.9 |  |  |  |
Board of Directors | Class A Common Stock |  |  |  |  |  |  |
Class of Stock |  |  |  |  |  |  |
Shares issued to directors during period |  |  | 19,081 |  |  |  |

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