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Commitments and Contingencies (Details) - USD ($) $ in Millions | Sep. 30, 2021 | Sep. 16, 2021 | Dec. 31, 2020
--- | --- | --- | ---
Class A Common Stock |  |  |
Loss Contingencies [Line Items] |  |  |
Shares outstanding (in shares) | 41,715,627 |  | 40,335,113
Entity Common Stock, Shares Outstanding | 41,715,627 |  |
Class A Common Stock | Great Western Bank |  |  |
Loss Contingencies [Line Items] |  |  |
Shares outstanding (in shares) |  | 0.8425 |
Common Stock, Value, Outstanding |  | $ 2,000.0 |
Mortgage Loans Held For Sale [Member] |  |  |
Loss Contingencies [Line Items] |  |  |
Mortgage loans with recourse provision in effect | $ 0.4 |  |
Construction Contracts |  |  |
Loss Contingencies [Line Items] |  |  |
Commitments under construction contracts | $ 3.3 |  |

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