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Investment Securities and Other Investments - Additional Information (Detail) - USD ($)
Sep. 30, 2025
Dec. 31, 2024
Schedule Of Investments [Line Items]    
Unrealized gain position $ 39,400,000 $ 1,100,000
Federal home loan bank stock 9,100,000 9,400,000
Federal reserve bank stock 9,400,000 9,400,000
Correspondent bank stock 500,000 500,000
Other equity investments 4,900,000 4,800,000
Other Investments, Total 20,804,000 19,405,000 [1]
Federal Reserve Board Bank Term Funding Program [Member]    
Schedule Of Investments [Line Items]    
Advance from federal reserve bank 0 0
Asset Pledged as Collateral without Right [Member] | FHLB [Member]    
Schedule Of Investments [Line Items]    
Securities pledged 176,600,000 268,900,000
Asset Pledged as Collateral without Right [Member] | FRB [Member]    
Schedule Of Investments [Line Items]    
Securities pledged 0 16,300,000
Third Party Investment Grade [Member]    
Schedule Of Investments [Line Items]    
Securities pledged $ 24,200,000 $ 29,300,000
[1] Derived from audited December 31, 2024 Consolidated Financial Statements.