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Securities - Additional Information (Detail)
 3 Months Ended 6 Months Ended
Jun. 30, 2025
USD ($)
Security
Jun. 30, 2024
USD ($)
Jun. 30, 2025
USD ($)
Security
Jun. 30, 2024
USD ($)
Dec. 31, 2024
USD ($)
Security
Debt Securities, Available-for-Sale [Line Items]          
Proceeds from sale of debt securities available-for-sale $ 0 $ 0 $ 0 $ 0  
Gross realized gains 0 0 0 0  
Gross realized losses 0 $ 0 0 $ 0  
Carrying value of pledged securities $ 213,729,000   $ 213,729,000   $ 206,600,000
Number of securities in portfolio with unrealized losses | Security 511   511   508
Available for sale term 3 years   3 years    
Equity securities $ 2,300,000   $ 2,300,000   $ 2,400,000
FHLBC stock 24,400,000   24,400,000   18,500,000
FRBC stock 11,500,000   11,500,000   11,500,000
Other securities 36,195,000   36,195,000   30,352,000
United Bankers Bancorp [Member]          
Debt Securities, Available-for-Sale [Line Items]          
Other securities 225,000   225,000   225,000
Farmer Mac [Member]          
Debt Securities, Available-for-Sale [Line Items]          
Other securities 42,000   42,000   42,000
Norwalk Community Development Corp [Member]          
Debt Securities, Available-for-Sale [Line Items]          
Other securities $ 2,000   $ 2,000   $ 2,000