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Commitments and Contingencies (Narrative) (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2024 | Mar. 31, 2023 | Dec. 31, 2023
Commitments and Contingencies Disclosure [Abstract] |  |  |
Financial guarantees in connection with standby letters of credit | $ 0.0 | $ 0.0 |
Standby letters of credit expiring within one year | 181.8 |  |
Standby letters of credit expiring thereafter | 14.9 |  |
Loss Contingency Accrual | 6.9 |  |
iCap Entities [Member] |  |  |
Concentration Risk [Line Items] |  |  |
Loss Contingency, Damages Sought, Value | 250.0 |  |
Professional Financial Investors, Inc. and Professional Investors Security Fund, Inc. [Member] |  |  |
Concentration Risk [Line Items] |  |  |
Prior Bankruptcy Recoveries by Plaintiffs | 110.0 |  |
Minimum | Professional Financial Investors, Inc. and Professional Investors Security Fund, Inc. [Member] |  |  |
Concentration Risk [Line Items] |  |  |
Loss Contingency, Damages Sought, Value | 386.2 |  |
Maximum | Professional Financial Investors, Inc. and Professional Investors Security Fund, Inc. [Member] |  |  |
Concentration Risk [Line Items] |  |  |
Loss Contingency, Damages Sought, Value | $ 429.8 |  |
Product Concentration Risk | Revenue Benchmark | Real Estate Loans As Part Of Loan Portfolio |  |  |
Concentration Risk [Line Items] |  |  |
Concentration risk (as a percent) | 75.00% |  | 75.00%
Product Concentration Risk | Revenue Benchmark | Multifamily Loans as Part of Loan portfolio [Member] |  |  |
Concentration Risk [Line Items] |  |  |
Concentration risk (as a percent) | 19.00% |  |
Product Concentration Risk | Revenue Benchmark | Commercial Office Loans as Part of Loan portfolio [Member] |  |  |
Concentration Risk [Line Items] |  |  |
Concentration risk (as a percent) | 8.00% |  |

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