Summary of Significant Accounting Policies - Additional Information (Detail)	1 Months Ended	3 Months Ended		6 Months Ended		7 Months Ended
	Sep. 30, 2023 $ / shares shares	Jun. 30, 2024 USD ($) shares	Jun. 30, 2023 USD ($) shares	Jun. 30, 2024 USD ($) Location shares	Jun. 30, 2023 USD ($) shares	Jul. 27, 2021 shares	Dec. 31, 2023 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
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		$ 441,557,000	$ 490,280,000	$ 441,557,000	$ 490,280,000		403,298,000
First financial antidilutive securities excluded from eps computation | shares		407,000	778,000	412,000	485,000
Shares repurchased under stock repurchase authorization, shares | shares	101,337
Deferred Tax Assets		$ 123,407,000	$ 133,016,000	$ 123,407,000	$ 133,016,000		110,800,000
Commitments to Extend Credit [Member]
Equity, Class of Treasury Stock [Line Items]
Reserve for unfunded commitments		7,433,000	9,448,000	7,433,000	9,448,000		7,903,000
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