Summary of Significant Accounting Policies - Additional Information (Detail)	1 Months Ended	2 Months Ended	9 Months Ended	12 Months Ended
	Jul. 23, 2024 shares	Jul. 31, 2022 $ / shares shares	Sep. 30, 2023 $ / shares shares	Dec. 31, 2024 USD ($) Location shares	Dec. 31, 2023 USD ($) shares	Dec. 31, 2022 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				$ 1,340,082,000	$ 1,219,525,000
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				$ 6,418,000	8,826,000
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 loss in available-for-sale securities, included in accumulated other comprehensive income				$ 424,289,000	$ 403,298,000
First financial antidilutive securities excluded from eps computation | shares				503,000	473,000	1,261,000
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				$ 8,677,000	$ 7,903,000
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