Summary of Significant Accounting Policies - Additional Information (Detail)	3 Months Ended		6 Months Ended		7 Months Ended
	Jun. 30, 2023 USD ($) shares	Jun. 30, 2022 USD ($) shares	Jun. 30, 2023 USD ($) Location $ / shares shares	Jun. 30, 2022 USD ($) shares	Jul. 27, 2021 shares	Dec. 31, 2022 USD ($)
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			$ 38.61
Minimum number of days to consider the loans as non-accrual			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	$ (490,280,000)	(400,514,000)	$ (490,280,000)	(400,514,000)		(535,228,000)
Retained earnings net of tax after transitional charges	$ 1,175,410,000	$ 1,052,453,000	$ 1,175,410,000	$ 1,052,453,000		1,121,945,000
First financial antidilutive securities excluded from eps computation | shares	778,000	207,000	485,000	209,000
Shares repurchased under stock repurchase authorization, shares | shares			244,559
Deferred Tax Assets	$ 133,016,000,000	$ 109,450,000,000	$ 133,016,000,000	$ 109,450,000,000		145,511,000,000
Common Stock [Member]
Equity, Class of Treasury Stock [Line Items]
Shares repurchased under stock repurchase authorization, shares | shares		(191,987)		(191,987)
Commitments to Extend Credit [Member]
Equity, Class of Treasury Stock [Line Items]
Reserve for unfunded commitments	9,449,000	$ 8,718,000	9,449,000	$ 8,718,000		12,323,000
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