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Securities - Additional Information (Details)
 3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2025
USD ($)
Security
Sep. 30, 2024
USD ($)
Jun. 30, 2024
USD ($)
shares
Sep. 30, 2025
USD ($)
Security
Segment
Sep. 30, 2024
USD ($)
Dec. 31, 2024
USD ($)
Security
Schedule Of Held To Maturity Securities [Line Items]            
Number of Investment Securities Segments | Segment       2    
Credit losses       $ 0    
Municipal securities percentage of securities portfolio 0.70%     0.70%    
Securities in Unrealized Loss Positions Qualitative Disclosure Number of Positions Greater Than or Equal to One Year | Security 756     756   949
Gain (loss) on sale of investment securities $ 0 $ 0   $ 0 $ (9,400,000)  
Available for Sale Securities, Amortized Cost Basis 334,356,000     334,356,000   $ 339,016,000
Debt Securities, Available-for-Sale 332,369,000     332,369,000   336,960,000
Collateralized Securities [Member]            
Schedule Of Held To Maturity Securities [Line Items]            
Available for Sale Securities, Amortized Cost Basis 7,510,000,000     7,510,000,000   10,260,000,000
Debt Securities, Available-for-Sale $ 6,780,000,000     $ 6,780,000,000   $ 8,910,000,000
Visa Stock Exchange [Member]            
Schedule Of Held To Maturity Securities [Line Items]            
Conversion of stock, description       During the second quarter of 2024, the Bank tendered all of its shares of Visa Class B-1 common stock in exchange for a combination of Visa Class B-2 common stock and Visa Class C common stock, pursuant to the terms and subject to the conditions of the public offering of Visa to exchange its Class B-1 common stock for a combination of shares of its Class B-2 common stock and Class C common stock, which expired on May 3, 2024.    
Gain on stock exchange     $ 20,600,000      
Class B-2 Common Stock [Member] | Visa Stock Exchange [Member]            
Schedule Of Held To Maturity Securities [Line Items]            
Conversion of stock, shares converted | shares     48,492      
Cost basis     $ 0      
Common Class C [Member] | Visa Stock Exchange [Member]            
Schedule Of Held To Maturity Securities [Line Items]            
Conversion of stock, shares converted | shares     19,245      
Securities Concentration Risk [Member] | Stockholders' Equity, Total [Member] | Other Than U.S. Government and Agencies [Member]            
Schedule Of Held To Maturity Securities [Line Items]            
Concentration Risk, Percentage       10.00%   10.00%