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Investment Securities - Summary of Investment Securities (Details) - USD ($) $ in Thousands | Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
--- | --- | --- | ---
Held-to-maturity |  |  |
Amortized Cost | $ 3,639,850 | $ 3,729,502 |
Allowance for Credit Losses | (3,214) | (3,214) | $ (1,388)
Net Carrying Amount | 3,636,636 | 3,726,288 |
Gross Unrealized Gains | 232 | 638 |
Gross Unrealized (Losses) | (686,917) | (591,556) |
Estimated Fair Value | 2,949,951 | 3,135,370 |
Available-for-sale |  |  |
Amortized Cost | 2,852,774 | 3,509,709 |
Allowance for Credit Losses | 0 | 0 | 0
Gross Unrealized Gains | 307 | 230 |
Gross Unrealized (Losses) | (323,655) | (357,786) |
Estimated Fair Value | 2,529,426 | 3,152,153 |
U.S. Treasury |  |  |
Available-for-sale |  |  |
Amortized Cost | 999 | 2,285 |
Allowance for Credit Losses | 0 | 0 |
Gross Unrealized Gains | 0 | 0 |
Gross Unrealized (Losses) | (3) | (31) |
Estimated Fair Value | 996 | 2,254 |
U.S. Government agencies |  |  |
Held-to-maturity |  |  |
Amortized Cost | 455,869 | 453,121 |
Allowance for Credit Losses | 0 | 0 |
Net Carrying Amount | 455,869 | 453,121 |
Gross Unrealized Gains | 0 | 0 |
Gross Unrealized (Losses) | (95,961) | (89,203) |
Estimated Fair Value | 359,908 | 363,918 |
Available-for-sale |  |  |
Amortized Cost | 55,589 | 74,460 |
Allowance for Credit Losses | 0 | 0 |
Gross Unrealized Gains | 5 | 35 |
Gross Unrealized (Losses) | (1,047) | (1,993) |
Estimated Fair Value | 54,547 | 72,502 |
Mortgage-backed securities |  |  |
Held-to-maturity |  |  |
Amortized Cost | 1,070,032 | 1,161,694 |
Allowance for Credit Losses | 0 | 0 |
Net Carrying Amount | 1,070,032 | 1,161,694 |
Gross Unrealized Gains | 212 | 354 |
Gross Unrealized (Losses) | (133,746) | (107,834) |
Estimated Fair Value | 936,498 | 1,054,214 |
Available-for-sale |  |  |
Amortized Cost | 1,545,539 | 2,138,652 |
Allowance for Credit Losses | 0 | 0 |
Gross Unrealized Gains | 4 | 8 |
Gross Unrealized (Losses) | (152,784) | (198,353) |
Estimated Fair Value | 1,392,759 | 1,940,307 |
State and political subdivisions |  |  |
Held-to-maturity |  |  |
Amortized Cost | 1,857,373 | 1,858,680 |
Allowance for Credit Losses | (196) | (2,006) | (110)
Net Carrying Amount | 1,857,177 | 1,856,674 |
Gross Unrealized Gains | 20 | 284 |
Gross Unrealized (Losses) | (436,061) | (369,509) |
Estimated Fair Value | 1,421,136 | 1,487,449 |
Available-for-sale |  |  |
Amortized Cost | 1,015,619 | 1,035,147 |
Allowance for Credit Losses | 0 | 0 | 0
Gross Unrealized Gains | 132 | 187 |
Gross Unrealized (Losses) | (157,569) | (132,541) |
Estimated Fair Value | 858,182 | 902,793 |
Other securities |  |  |
Held-to-maturity |  |  |
Amortized Cost | 256,576 | 256,007 |
Allowance for Credit Losses | (3,018) | (1,208) | (1,278)
Net Carrying Amount | 253,558 | 254,799 |
Gross Unrealized Gains | 0 | 0 |
Gross Unrealized (Losses) | (21,149) | (25,010) |
Estimated Fair Value | 232,409 | 229,789 |
Available-for-sale |  |  |
Amortized Cost | 235,028 | 259,165 |
Allowance for Credit Losses | 0 | 0 | $ 0
Gross Unrealized Gains | 166 | 0 |
Gross Unrealized (Losses) | (12,252) | (24,868) |
Estimated Fair Value | $ 222,942 | $ 234,297 |

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