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Securities - Additional Information (Detail) | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2025 USD ($) Investment | Sep. 30, 2024 USD ($) | Sep. 30, 2025 USD ($) Investment | Sep. 30, 2024 USD ($) | Dec. 31, 2024
Interest Bearing Time Deposits In Banks And Securities [Line Items] |  |  |  |  |
Interest-bearing time deposits, maturity period, years | 12 months | 12 months | 12 months | 12 months | 12 months
Number of investment positions | Investment | 682 |  | 682 |  |
Securities pledged as collateral | $ 2,335,928,000 |  | $ 2,335,928,000 |  |
Debt Securities, Available-for-Sale, Realized Gain | 0 | $ 0 | 0 | $ 0 |
Available-for-Sale Securities [Member] |  |  |  |  |
Interest Bearing Time Deposits In Banks And Securities [Line Items] |  |  |  |  |
Sales of investment securities available-for-sale | $ 0 | $ 0 | $ 0 | $ 0 |
Obligations of State and Political Subdivisions [Member] | Texas [Member] |  |  |  |  |
Interest Bearing Time Deposits In Banks And Securities [Line Items] |  |  |  |  |
Percentage of securities guaranteed by Texas Permanent School Fund | 55.25% |  | 55.25% |  |
Obligations of State and Political Subdivisions [Member] | Texas [Member] | Available-for-Sale Securities [Member] | Geographic Concentration Risk [Member] |  |  |  |  |
Interest Bearing Time Deposits In Banks And Securities [Line Items] |  |  |  |  |
Concentration risk threshold percentage |  |  | 72.57% |  |

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