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v3.21.2

Investment Securities - Summary of Investment Securities (Details) - USD ($) $ in Thousands | Sep. 30, 2021 | Jun. 30, 2021 | Dec. 31, 2020 | Sep. 30, 2020 | Jun. 30, 2020 | Dec. 31, 2019
--- | --- | --- | --- | --- | --- | ---
Held-to-maturity |  |  |  |  |  |
Amortized Cost | $ 1,518,076 |  | $ 335,946 |  |  |
Allowance for credit losses on HTM | (1,279) | $ (1,132) | (2,915) | $ (373) | $ (307) | $ 0
Net Carrying Amount | 1,516,797 |  | 333,031 |  |  |
Gross Unrealized Gains | 2,623 |  | 8,924 |  |  |
Gross Unrealized (Losses) | (31,504) |  | (30) |  |  |
Estimated Fair Value | 1,487,916 |  | 341,925 |  |  |
Available-for-sale |  |  |  |  |  |
Amortized Cost | 6,838,743 |  | 3,397,043 |  |  |
Allowance for credit losses on AFS | 0 | 0 | (312) | (1,208) | (609) | 0
Gross Unrealized Gains | 40,581 |  | 79,663 |  |  |
Gross Unrealized (Losses) | (57,121) |  | (2,796) |  |  |
Estimated Fair Value | 6,822,203 |  | 3,473,598 |  |  |
U.S. Treasury |  |  |  |  |  |
Available-for-sale |  |  |  |  |  |
Amortized Cost | 300 |  |  |  |  |
Allowance for credit losses on AFS | 0 |  |  |  |  |
Gross Unrealized Gains | 0 |  |  |  |  |
Gross Unrealized (Losses) | 0 |  |  |  |  |
Estimated Fair Value | 300 |  |  |  |  |
U.S. Government agencies |  |  |  |  |  |
Held-to-maturity |  |  |  |  |  |
Amortized Cost | 232,549 |  |  |  |  |
Allowance for credit losses on HTM | 0 |  |  |  |  |
Net Carrying Amount | 232,549 |  |  |  |  |
Gross Unrealized Gains | 0 |  |  |  |  |
Gross Unrealized (Losses) | (5,179) |  |  |  |  |
Estimated Fair Value | 227,370 |  |  |  |  |
Available-for-sale |  |  |  |  |  |
Amortized Cost | 361,452 |  | 477,693 |  |  |
Allowance for credit losses on AFS | 0 |  | 0 |  |  |
Gross Unrealized Gains | 635 |  | 844 |  |  |
Gross Unrealized (Losses) | (7,705) |  | (1,300) |  |  |
Estimated Fair Value | 354,382 |  | 477,237 |  |  |
Mortgage-backed securities |  |  |  |  |  |
Held-to-maturity |  |  |  |  |  |
Amortized Cost | 57,930 |  | 22,354 |  |  |
Allowance for credit losses on HTM | 0 |  | 0 |  |  |
Net Carrying Amount | 57,930 |  | 22,354 |  |  |
Gross Unrealized Gains | 417 |  | 683 |  |  |
Gross Unrealized (Losses) | (1,024) |  | 0 |  |  |
Estimated Fair Value | 57,323 |  | 23,037 |  |  |
Available-for-sale |  |  |  |  |  |
Amortized Cost | 4,434,981 |  | 1,374,769 |  |  |
Allowance for credit losses on AFS | 0 |  | 0 |  |  |
Gross Unrealized Gains | 14,741 |  | 21,261 |  |  |
Gross Unrealized (Losses) | (28,102) |  | (1,094) |  |  |
Estimated Fair Value | 4,421,620 |  | 1,394,936 |  |  |
State and political subdivisions |  |  |  |  |  |
Held-to-maturity |  |  |  |  |  |
Amortized Cost | 1,210,287 |  | 312,416 |  |  |
Allowance for credit losses on HTM | (1,196) | (871) | (2,307) | (73) | (95) | 0
Net Carrying Amount | 1,209,091 |  | 310,109 |  |  |
Gross Unrealized Gains | 2,206 |  | 8,148 |  |  |
Gross Unrealized (Losses) | (24,962) |  | (30) |  |  |
Estimated Fair Value | 1,186,335 |  | 318,227 |  |  |
Available-for-sale |  |  |  |  |  |
Amortized Cost | 1,574,674 |  | 1,416,136 |  |  |
Allowance for credit losses on AFS | 0 | 0 | (217) | (1,148) | (371) | 0
Gross Unrealized Gains | 17,877 |  | 55,111 |  |  |
Gross Unrealized (Losses) | (17,343) |  | (307) |  |  |
Estimated Fair Value | 1,575,208 |  | 1,470,723 |  |  |
Other securities |  |  |  |  |  |
Held-to-maturity |  |  |  |  |  |
Amortized Cost | 17,310 |  | 1,176 |  |  |
Allowance for credit losses on HTM | (83) | (261) | (608) | (300) | (212) | 0
Net Carrying Amount | 17,227 |  | 568 |  |  |
Gross Unrealized Gains | 0 |  | 93 |  |  |
Gross Unrealized (Losses) | (339) |  | 0 |  |  |
Estimated Fair Value | 16,888 |  | 661 |  |  |
Available-for-sale |  |  |  |  |  |
Amortized Cost | 467,336 |  | 128,445 |  |  |
Allowance for credit losses on AFS | 0 | $ 0 | (95) | $ (60) | $ (238) | $ 0
Gross Unrealized Gains | 7,328 |  | 2,447 |  |  |
Gross Unrealized (Losses) | (3,971) |  | (95) |  |  |
Estimated Fair Value | $ 470,693 |  | $ 130,702 |  |  |

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