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Summary of Significant Accounting Policies - Additional Information (Detail)
 1 Months Ended 3 Months Ended 9 Months Ended
Jul. 22, 2025
shares
Sep. 30, 2023
$ / shares
shares
Sep. 30, 2025
USD ($)
shares
Sep. 30, 2024
USD ($)
shares
Sep. 30, 2025
USD ($)
Location
shares
Sep. 30, 2024
USD ($)
shares
Dec. 31, 2024
USD ($)
Equity, Class of Treasury Stock [Line Items]              
Number of locations | Location         79    
Minimum number of shares that company is required to repurchase | shares 0            
Stock repurchase program, number of shares authorized to be repurchased | shares 5,000,000            
Amount of allowance for credit loss     $ 0 $ 0 $ 0 $ 0 $ 0
Shares repurchased and retired average price | $ / shares   $ 26.99          
Minimum number of days to consider the loans as non-accrual         90 days 90 days  
Impairment recorded         $ 0 $ 0  
Other identifiable intangible assets, amortized period (years)     7 years   7 years    
Securities sold under agreements to repurchase maturity range (in days)         one to four days    
Interest-bearing time deposits, maturity period (in days)         90 days or less    
Unrealized net losses in available-for-sale securities, included in accumulated other comprehensive income     $ 308,579,000 $ 329,817,000 $ 308,579,000 $ 329,817,000 424,289,000
First financial antidilutive securities excluded from eps computation | shares     474,000 375,000 401,000 449,000  
Shares repurchased under stock repurchase authorization, shares | shares   101,337     0 0  
Deferred Tax Assets     $ 96,564,000 $ 94,239,000 $ 96,564,000 $ 94,239,000 116,999,000
Commitments to Extend Credit [Member]              
Equity, Class of Treasury Stock [Line Items]              
Reserve for unfunded commitments     8,842,000 8,004,000 8,842,000 8,004,000 8,677,000
Held-to-maturity Securities [Member]              
Equity, Class of Treasury Stock [Line Items]              
Securities held to maturity     $ 0 $ 0 $ 0 $ 0 $ 0