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Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)
$ in Millions
Jan. 31, 2025
Sep. 30, 2025
Sep. 30, 2024
Summary Of Significant Accounting Policies [Line Items]      
Interest bearing amounts held at other financial institutions   $ 124.0 $ 103.2
Heartland Financial USA Inc [Member]      
Summary Of Significant Accounting Policies [Line Items]      
Description of acquired entity On January 31, 2025 (Acquisition Date), the Company acquired Heartland Financial USA, Inc. (HTLF) pursuant to an Agreement and Plan of Merger, dated as of April 28, 2024.    
Acquisition date Jan. 31, 2025    
Name of acquired entity Heartland Financial USA, Inc. (HTLF)    
Date of merger Apr. 28, 2024