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v3.23.3

Investment Securities - Summary of Investment Securities (Details) - USD ($) $ in Thousands | Sep. 30, 2023 | Jun. 30, 2023 | Dec. 31, 2022 | Sep. 30, 2022 | Jun. 30, 2022 | Dec. 31, 2021
--- | --- | --- | --- | --- | --- | ---
Held-to-maturity |  |  |  |  |  |
Amortized Cost | $ 3,745,506 |  | $ 3,761,094 |  |  |
Allowance for credit losses on HTM | (3,214) | $ (3,214) | (1,388) | $ (1,384) | $ (1,381) | $ (1,279)
Net Carrying Amount | 3,742,292 |  | 3,759,706 |  |  |
Gross Unrealized Gains | 26 |  | 283 |  |  |
Gross Unrealized (Losses) | (894,107) |  | (696,756) |  |  |
Estimated Fair Value | 2,848,211 |  | 3,063,233 |  |  |
Available-for-sale |  |  |  |  |  |
Amortized Cost | 3,890,910 |  | 4,331,413 |  |  |
Allowance for Credit Losses | (1,196) | (2,396) | 0 |  |  |
Gross Unrealized Gains | 156 |  | 373 |  |  |
Gross Unrealized (Losses) | (531,449) |  | (478,932) |  |  |
Estimated Fair Value | 3,358,421 |  | 3,852,854 |  |  |
U.S. Government agencies |  |  |  |  |  |
Held-to-maturity |  |  |  |  |  |
Amortized Cost | 452,428 |  | 448,012 |  |  |
Allowance for credit losses on HTM | 0 |  | 0 |  |  |
Net Carrying Amount | 452,428 |  | 448,012 |  |  |
Gross Unrealized Gains | 0 |  | 0 |  |  |
Gross Unrealized (Losses) | (117,530) |  | (102,558) |  |  |
Estimated Fair Value | 334,898 |  | 345,454 |  |  |
Available-for-sale |  |  |  |  |  |
Amortized Cost | 179,638 |  | 191,498 |  |  |
Allowance for Credit Losses | 0 |  | 0 |  |  |
Gross Unrealized Gains | 45 |  | 103 |  |  |
Gross Unrealized (Losses) | (6,924) |  | (7,322) |  |  |
Estimated Fair Value | 172,759 |  | 184,279 |  |  |
U.S. Treasury |  |  |  |  |  |
Available-for-sale |  |  |  |  |  |
Amortized Cost | 2,278 |  | 2,257 |  |  |
Allowance for Credit Losses | 0 |  | 0 |  |  |
Gross Unrealized Gains | 0 |  | 0 |  |  |
Gross Unrealized (Losses) | (54) |  | (60) |  |  |
Estimated Fair Value | 2,224 |  | 2,197 |  |  |
Mortgage-backed securities |  |  |  |  |  |
Held-to-maturity |  |  |  |  |  |
Amortized Cost | 1,178,324 |  | 1,190,781 |  |  |
Allowance for credit losses on HTM | 0 |  | 0 |  |  |
Net Carrying Amount | 1,178,324 |  | 1,190,781 |  |  |
Gross Unrealized Gains | 0 |  | 227 |  |  |
Gross Unrealized (Losses) | (172,976) |  | (118,960) |  |  |
Estimated Fair Value | 1,005,348 |  | 1,072,048 |  |  |
Available-for-sale |  |  |  |  |  |
Amortized Cost | 2,444,803 |  | 2,809,319 |  |  |
Allowance for Credit Losses | 0 |  | 0 |  |  |
Gross Unrealized Gains | 0 |  | 20 |  |  |
Gross Unrealized (Losses) | (287,711) |  | (266,437) |  |  |
Estimated Fair Value | 2,157,092 |  | 2,542,902 |  |  |
State and political subdivisions |  |  |  |  |  |
Held-to-maturity |  |  |  |  |  |
Amortized Cost | 1,859,172 |  | 1,861,102 |  |  |
Allowance for credit losses on HTM | (1,520) | (934) | (110) | (107) | (103) | (1,197)
Net Carrying Amount | 1,857,652 |  | 1,860,992 |  |  |
Gross Unrealized Gains | 26 |  | 56 |  |  |
Gross Unrealized (Losses) | (564,366) |  | (446,198) |  |  |
Estimated Fair Value | 1,293,312 |  | 1,414,850 |  |  |
Available-for-sale |  |  |  |  |  |
Amortized Cost | 999,373 |  | 1,056,124 |  |  |
Allowance for Credit Losses | 0 | 0 | 0 |  |  |
Gross Unrealized Gains | 111 |  | 250 |  |  |
Gross Unrealized (Losses) | (209,140) |  | (185,300) |  |  |
Estimated Fair Value | 790,344 |  | 871,074 |  |  |
Other securities |  |  |  |  |  |
Held-to-maturity |  |  |  |  |  |
Amortized Cost | 255,582 |  | 261,199 |  |  |
Allowance for credit losses on HTM | (1,694) | (2,280) | (1,278) | $ (1,277) | $ (1,278) | $ (82)
Net Carrying Amount | 253,888 |  | 259,921 |  |  |
Gross Unrealized Gains | 0 |  | 0 |  |  |
Gross Unrealized (Losses) | (39,235) |  | (29,040) |  |  |
Estimated Fair Value | 214,653 |  | 230,881 |  |  |
Available-for-sale |  |  |  |  |  |
Amortized Cost | 264,818 |  | 272,215 |  |  |
Allowance for Credit Losses | (1,196) | $ (2,396) | 0 |  |  |
Gross Unrealized Gains | 0 |  | 0 |  |  |
Gross Unrealized (Losses) | (27,620) |  | (19,813) |  |  |
Estimated Fair Value | $ 236,002 |  | $ 252,402 |  |  |

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