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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%