Summary of Significant Accounting Policies - Additional Information (Detail)	1 Months Ended	3 Months Ended		7 Months Ended
	Sep. 30, 2023 $ / shares shares	Mar. 31, 2024 USD ($) Location shares	Mar. 31, 2023 USD ($) 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
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
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		$ 441,227,000	$ 458,249,000		403,298,000
First financial antidilutive securities excluded from eps computation | shares		417,000	480,000
Shares repurchased under stock repurchase authorization, shares | shares	101,337
Deferred Tax Assets		$ 122,844,000	$ 122,947,000		110,800,000
Commitments to Extend Credit [Member]
Equity, Class of Treasury Stock [Line Items]
Reserve for unfunded commitments		7,455,000	10,397,000		7,903,000
Held-to-maturity Securities [Member]
Equity, Class of Treasury Stock [Line Items]
Securities held to maturity		$ 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