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Commitments and Contingencies (Narrative) (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
Sep. 30, 2024 | Sep. 30, 2023 | Sep. 30, 2024 | Sep. 30, 2023 | Dec. 31, 2023
Commitments and Contingencies Disclosure [Abstract] |  |  |  |  |
Financial guarantees in connection with standby letters of credit | $ 0.0 | $ 0.0 | $ 0.0 | $ 0.0 |
Standby letters of credit expiring within one year | 203.3 |  | 203.3 |  |
Standby letters of credit expiring thereafter | 35.4 |  | 35.4 |  |
Loss Contingency Accrual | 2.4 |  | 2.4 |  |
Concentration Risk [Line Items] |  |  |  |  |
Prior Bankruptcy Recoveries by Plaintiffs | $ 110.0 |  | 110.0 |  |
iCap Entities [Member] |  |  |  |  |
Concentration Risk [Line Items] |  |  |  |  |
Number of Defendant Entities |  |  |  | 34 |
Loss Contingency, Damages Sought, Value |  |  | 290.0 |  |
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% |  | 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% |  | 8.00%

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