Securities - Additional Information (Detail) - USD ($) $ in Thousands |
Mar. 31, 2025 |
Dec. 31, 2024 |
|---|---|---|
| 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 | 71.30% | |
| 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 | 19,900 | 37,800 |
| Available-for-sale Securities [Member] | ||
| Schedule Of Marketable Securities [Line Items] | ||
| Carry Value of Securities Pledged | 6,100,000 | 6,200,000 |
| Accrued interest receivable | $ 86,200 | $ 104,900 |