Securities - Additional Information (Detail) - USD ($) $ in Thousands	Mar. 31, 2026	Dec. 31, 2025
Schedule Of Marketable Securities [Line Items]
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	69.80%
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	1,300,000	1,400,000
Accrued interest receivable	19,400	37,200
Available-for-sale Securities [Member]
Schedule Of Marketable Securities [Line Items]
Carry Value of Securities Pledged	5,800,000	6,600,000
Accrued interest receivable	$ 76,500	$ 122,500