Summary of Significant Accounting Policies - Additional Information (Detail)	2 Months Ended	7 Months Ended	9 Months Ended	12 Months Ended
	Jul. 31, 2022 $ / shares shares	Jul. 27, 2021 shares	Sep. 30, 2023 shares	Dec. 31, 2023 USD ($) Location $ / shares shares	Dec. 31, 2022 USD ($) shares	Dec. 31, 2021 USD ($) shares
Equity Class Of Treasury Stock [Line Items]
Number of locations | Location				79
Common stock, shares authorized | shares				200,000,000	200,000,000
Minimum number of shares that company is required to repurchase | shares		0
Shares repurchased under stock repurchase authorization, shares | shares	244,559		101,337
Retained earnings net of tax after transitional charges				$ 1,219,525,000	$ 1,121,945,000
Minimum number of days to consider the loans as non-accrual				90 days
Amount of allowance for credit loss				$ 0	0
Other identifiable intangible assets, amortized period (years)				7 years
Goodwill and intangible assets with indefinite lives				$ 313,481,000	313,481,000
Impairment recorded				0	0	$ 0
Carrying amount of goodwill arising from acquisitions, is deductible for federal income tax purposes				$ 8,826,000	11,233,000
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 gains in available-for-sale securities, included in accumulated other comprehensive income				$ (403,298,000)	$ (535,228,000)
First financial antidilutive securities excluded from eps computation | shares				473,000	1,261,000	0
Average Price of share repurchase | $ / shares	$ 38.61			$ 26.99
Commitments to Extend Credit [Member]
Equity Class Of Treasury Stock [Line Items]
Reserve for unfunded commitments				$ 7,903,000	$ 12,323,000
Held-to-maturity Securities [Member]
Equity Class Of Treasury Stock [Line Items]
Securities held to maturity				$ 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