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Securities (Securities Moody's and Standard & Poor's Bond Rating) (Details) - USD ($) $ in Thousands | Dec. 31, 2023 | Dec. 31, 2022
--- | --- | ---
Schedule of Held-to-maturity Securities [Line Items] |  |
Held to Maturity, Amortized Cost | $ 3,619,738 | $ 2,639,241
States and Political Subdivisions [Member] |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Held to Maturity, Amortized Cost | 2,367,807 | 2,111,619
States and Political Subdivisions [Member] | Not Guaranteed or Pre-Refunded [Member] |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Held to Maturity, Amortized Cost | 804,737 |
States and Political Subdivisions [Member] | Guaranteed by the Texas PSF [Member] |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Held to Maturity, Amortized Cost | 1,541,913 |
States and Political Subdivisions [Member] | Guaranteed by Third Party |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Held to Maturity, Amortized Cost | 19,756 |
States and Political Subdivisions [Member] | Pre-Refunded [Member] |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Held to Maturity, Amortized Cost | 1,401 |
Other [Member] |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Held to Maturity, Amortized Cost | 1,500 | $ 1,500
Aaa/AAA [Member] | States and Political Subdivisions [Member] |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Held to Maturity, Amortized Cost | 1,858,686 |
Aaa/AAA [Member] | States and Political Subdivisions [Member] | Not Guaranteed or Pre-Refunded [Member] |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Held to Maturity, Amortized Cost | 301,721 |
Aaa/AAA [Member] | States and Political Subdivisions [Member] | Guaranteed by the Texas PSF [Member] |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Held to Maturity, Amortized Cost | 1,541,913 |
Aaa/AAA [Member] | States and Political Subdivisions [Member] | Guaranteed by Third Party |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Held to Maturity, Amortized Cost | 13,651 |
Aaa/AAA [Member] | States and Political Subdivisions [Member] | Pre-Refunded [Member] |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Held to Maturity, Amortized Cost | 1,401 |
Aaa/AAA [Member] | Other [Member] |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Held to Maturity, Amortized Cost | 0 |
Aa/AA [Member] | States and Political Subdivisions [Member] |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Held to Maturity, Amortized Cost | 509,121 |
Aa/AA [Member] | States and Political Subdivisions [Member] | Not Guaranteed or Pre-Refunded [Member] |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Held to Maturity, Amortized Cost | 503,016 |
Aa/AA [Member] | States and Political Subdivisions [Member] | Guaranteed by the Texas PSF [Member] |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Held to Maturity, Amortized Cost | 0 |
Aa/AA [Member] | States and Political Subdivisions [Member] | Guaranteed by Third Party |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Held to Maturity, Amortized Cost | 6,105 |
Aa/AA [Member] | States and Political Subdivisions [Member] | Pre-Refunded [Member] |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Held to Maturity, Amortized Cost | 0 |
Aa/AA [Member] | Other [Member] |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Held to Maturity, Amortized Cost | 0 |
Not rated [Member] | States and Political Subdivisions [Member] |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Held to Maturity, Amortized Cost | 0 |
Not rated [Member] | States and Political Subdivisions [Member] | Not Guaranteed or Pre-Refunded [Member] |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Held to Maturity, Amortized Cost | 0 |
Not rated [Member] | States and Political Subdivisions [Member] | Guaranteed by the Texas PSF [Member] |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Held to Maturity, Amortized Cost | 0 |
Not rated [Member] | States and Political Subdivisions [Member] | Guaranteed by Third Party |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Held to Maturity, Amortized Cost | 0 |
Not rated [Member] | States and Political Subdivisions [Member] | Pre-Refunded [Member] |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Held to Maturity, Amortized Cost | 0 |
Not rated [Member] | Other [Member] |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Held to Maturity, Amortized Cost | $ 1,500 |

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