Securities - Additional Information (Detail) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Schedule Of Marketable Securities [Line Items]
AOCI, Debt Securities, Available-for-sale, Adjustment, Pre Tax	$ 685	$ 1,200
Net unamortized unrealized gain on transferred securities included in accumulated other comprehensive income, net of tax	$ 541	909
Percent Municipal Bond Portfolio Issued By Political Subdivision Or Agencies Within State Of Texas Guaranteed By Texas Permanent School Fund Or Have Been Pre-Refunded	72.60%
Debt Securities, Available-for-sale, Allowance for Credit Loss	$ 0	0
Held-to-maturity Securities [Member]
Schedule Of Marketable Securities [Line Items]
Carry Value of Securities Pledged	1,000,000	1,000,000
Accrued interest receivable	20,200	40,900
Available-for-sale Securities [Member]
Schedule Of Marketable Securities [Line Items]
Carry Value of Securities Pledged	5,400,000	6,100,000
Accrued interest receivable	$ 75,800	$ 114,900