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Securities - Additional Information (Detail) - USD ($) $ in Thousands | Jun. 30, 2025 | Dec. 31, 2024
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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 | 69.50% |
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 | 37,400 | 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 | $ 117,200 | $ 104,900

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