Summary of Significant Accounting Policies - Additional Information (Detail)	1 Months Ended		3 Months Ended		6 Months Ended
	Jul. 22, 2025 shares	Sep. 30, 2023 $ / shares shares	Jun. 30, 2025 USD ($) shares	Jun. 30, 2024 USD ($) shares	Jun. 30, 2025 USD ($) Location shares	Jun. 30, 2024 USD ($) shares	Dec. 31, 2024 USD ($)	Jul. 23, 2024 shares
Equity, Class of Treasury Stock [Line Items]
Number of locations | Location					79
Minimum number of shares that company is required to repurchase | shares	0
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			$ 373,456,000	$ 441,557,000	$ 373,456,000	$ 441,557,000	424,289,000
First financial antidilutive securities excluded from eps computation | shares			360,000	407,000	364,000	412,000
Shares repurchased under stock repurchase authorization, shares | shares		101,337			0
Deferred Tax Assets			$ 113,810,000	$ 123,407,000	$ 113,810,000	$ 123,407,000	116,999,000
Commitments to Extend Credit [Member]
Equity, Class of Treasury Stock [Line Items]
Reserve for unfunded commitments			9,914,000	7,433,000	9,914,000	7,433,000	8,677,000
Held-to-maturity Securities [Member]
Equity, Class of Treasury Stock [Line Items]
Securities held to maturity			$ 0	$ 0	$ 0	$ 0	$ 0
Maximum [Member]
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, number of shares authorized to be repurchased | shares	5,000,000							5,000,000