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v3.21.2

Investment Securities - Summary of Investment Securities (Details) - USD ($) $ in Thousands | Jun. 30, 2021 | Mar. 31, 2021 | Dec. 31, 2020 | Jun. 30, 2020 | Mar. 31, 2020 | Dec. 31, 2019
--- | --- | --- | --- | --- | --- | ---
Held-to-maturity |  |  |  |  |  |
Amortized Cost | $ 932,484 |  | $ 335,946 |  |  |
Allowance for credit losses on HTM | (1,132) | $ (1,618) | (2,915) | $ (307) | $ (409) | $ 0
Net Carrying Amount | 931,352 |  | 333,031 |  |  |
Gross Unrealized Gains | 9,550 |  | 8,924 |  |  |
Gross Unrealized (Losses) | (5,306) |  | (30) |  |  |
Estimated Fair Value | 935,596 |  | 341,925 |  |  |
Available-for-sale |  |  |  |  |  |
Amortized Cost | 6,543,022 |  | 3,397,043 |  |  |
Allowance for credit losses on AFS | 0 | (2,454) | (312) | (609) | (269) | 0
Gross Unrealized Gains | 59,361 |  | 79,663 |  |  |
Gross Unrealized (Losses) | (45,802) |  | (2,796) |  |  |
Estimated Fair Value | 6,556,581 |  | 3,473,598 |  |  |
U.S. Treasury |  |  |  |  |  |
Available-for-sale |  |  |  |  |  |
Amortized Cost | 600 |  |  |  |  |
Allowance for credit losses on AFS | 0 |  |  |  |  |
Gross Unrealized Gains | 0 |  |  |  |  |
Gross Unrealized (Losses) | 0 |  |  |  |  |
Estimated Fair Value | 600 |  |  |  |  |
U.S. Government agencies |  |  |  |  |  |
Held-to-maturity |  |  |  |  |  |
Amortized Cost | 77,396 |  |  |  |  |
Allowance for credit losses on HTM | 0 |  |  |  |  |
Net Carrying Amount | 77,396 |  |  |  |  |
Gross Unrealized Gains | 0 |  |  |  |  |
Gross Unrealized (Losses) | (2,054) |  |  |  |  |
Estimated Fair Value | 75,342 |  |  |  |  |
Available-for-sale |  |  |  |  |  |
Amortized Cost | 567,722 |  | 477,693 |  |  |
Allowance for credit losses on AFS | 0 |  | 0 |  |  |
Gross Unrealized Gains | 720 |  | 844 |  |  |
Gross Unrealized (Losses) | (13,505) |  | (1,300) |  |  |
Estimated Fair Value | 554,937 |  | 477,237 |  |  |
Mortgage-backed securities |  |  |  |  |  |
Held-to-maturity |  |  |  |  |  |
Amortized Cost | 60,649 |  | 22,354 |  |  |
Allowance for credit losses on HTM | 0 |  | 0 |  |  |
Net Carrying Amount | 60,649 |  | 22,354 |  |  |
Gross Unrealized Gains | 474 |  | 683 |  |  |
Gross Unrealized (Losses) | (729) |  | 0 |  |  |
Estimated Fair Value | 60,394 |  | 23,037 |  |  |
Available-for-sale |  |  |  |  |  |
Amortized Cost | 3,996,823 |  | 1,374,769 |  |  |
Allowance for credit losses on AFS | 0 |  | 0 |  |  |
Gross Unrealized Gains | 13,405 |  | 21,261 |  |  |
Gross Unrealized (Losses) | (23,019) |  | (1,094) |  |  |
Estimated Fair Value | 3,987,209 |  | 1,394,936 |  |  |
State and political subdivisions |  |  |  |  |  |
Held-to-maturity |  |  |  |  |  |
Amortized Cost | 794,178 |  | 312,416 |  |  |
Allowance for credit losses on HTM | (871) | (1,042) | (2,307) | (95) | (97) | 0
Net Carrying Amount | 793,307 |  | 310,109 |  |  |
Gross Unrealized Gains | 8,118 |  | 8,148 |  |  |
Gross Unrealized (Losses) | (2,523) |  | (30) |  |  |
Estimated Fair Value | 798,902 |  | 318,227 |  |  |
Available-for-sale |  |  |  |  |  |
Amortized Cost | 1,526,833 |  | 1,416,136 |  |  |
Allowance for credit losses on AFS | 0 | (64) | (217) | (371) | (95) | 0
Gross Unrealized Gains | 36,945 |  | 55,111 |  |  |
Gross Unrealized (Losses) | (6,281) |  | (307) |  |  |
Estimated Fair Value | 1,557,497 |  | 1,470,723 |  |  |
Other securities |  |  |  |  |  |
Held-to-maturity |  |  |  |  |  |
Amortized Cost | 261 |  | 1,176 |  |  |
Allowance for credit losses on HTM | (261) | (576) | (608) | (212) | (312) | 0
Net Carrying Amount | 0 |  | 568 |  |  |
Gross Unrealized Gains | 958 |  | 93 |  |  |
Gross Unrealized (Losses) | 0 |  | 0 |  |  |
Estimated Fair Value | 958 |  | 661 |  |  |
Available-for-sale |  |  |  |  |  |
Amortized Cost | 451,044 |  | 128,445 |  |  |
Allowance for credit losses on AFS | 0 | $ (2,390) | (95) | $ (238) | $ (174) | $ 0
Gross Unrealized Gains | 8,291 |  | 2,447 |  |  |
Gross Unrealized (Losses) | (2,997) |  | (95) |  |  |
Estimated Fair Value | $ 456,338 |  | $ 130,702 |  |  |

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