Summary of Significant Accounting Policies - Additional Information (Detail)	3 Months Ended		7 Months Ended	9 Months Ended		14 Months Ended
	Sep. 30, 2022 USD ($) shares	Sep. 30, 2021 USD ($) shares	Jul. 27, 2021 shares	Sep. 30, 2022 USD ($) Location shares	Sep. 30, 2021 USD ($) shares	Sep. 30, 2022 USD ($) $ / shares shares	Dec. 31, 2021 USD ($)
Equity, Class of Treasury Stock [Line Items]
Number of locations | Location				78
Minimum number of shares that company is required to repurchase | shares			0
Amount of allowance for credit loss	$ 0	$ 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
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 (losses) in available-for-sale securities, included in accumulated other comprehensive income	(632,421,000)	109,447,000		$ (632,421,000)	109,447,000	$ (632,421,000)	99,253,000
Retained earnings net of tax after transitional charges	$ 1,087,543,000	$ 947,724,000		$ 1,087,543,000	$ 947,724,000	$ 1,087,543,000	981,675,000
First financial antidilutive securities excluded from eps computation | shares	346,000	127,000		272,000	46,000
Shares repurchased under stock repurchase authorization, shares | shares						244,559
Deferred Tax Assets	$ 168,398,000			$ 168,398,000		$ 168,398,000
Deferred Tax Liabilities		$ 27,524,000			$ 27,524,000		24,817,000
Common Stock [Member]
Equity, Class of Treasury Stock [Line Items]
Shares repurchased under stock repurchase authorization, shares | shares	(52,572)			(244,559)
Commitments to Extend Credit [Member]
Equity, Class of Treasury Stock [Line Items]
Reserve for unfunded commitments	$ 10,879,000	6,751,000		$ 10,879,000	6,751,000	10,879,000	6,436,000
Held-to-maturity Securities [Member]
Equity, Class of Treasury Stock [Line Items]
Securities held to maturity	$ 0	$ 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