Securities - Additional Information (Detail) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Schedule Of Marketable Securities [Line Items]
Carrying value of pledged securities held to maturity	$ 3,711,579	$ 2,639,083
AOCI, Debt Securities, Available-for-sale, Adjustment, Pre Tax	1,600	1,800
Net unamortized unrealized gain on transferred securities included in accumulated other comprehensive income, net of tax	$ 1,300	1,400
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	75.90%
Carrying value of pledged securities, available-for-sale	$ 17,981,830	18,243,605
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Held-to-maturity Securities [Member]
Schedule Of Marketable Securities [Line Items]
Accrued interest receivable	20,600	30,200
Carry Value of Securities Pledged	438,000	256,300
Available-for-sale Securities [Member]
Schedule Of Marketable Securities [Line Items]
Accrued interest receivable	91,400	140,600
Carry Value of Securities Pledged	$ 6,900,000	$ 8,000,000