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Investment Securities (Details) - USD ($) $ in Thousands | Apr. 01, 2021 | Sep. 30, 2021 | Dec. 31, 2020
--- | --- | --- | ---
Investment securities available-for-sale |  |  |
Amortized Cost |  | $ 655,560 | $ 578,138
Unrealized Gains |  | 7,212 | 14,749
Unrealized Losses |  | (7,490) | (545)
Fair Value |  | 655,282 | 592,342
Amortized Cost |  | 362,586 |
Unrealized Gains |  | 1,585 |
Unrealized Losses |  | (631) |
Fair Value |  | 363,540 |
Amortized Cost |  | 1,018,146 |
Unrealized Gains |  | 8,797 |
Unrealized Losses |  | (8,121) |
Fair Value |  | 1,018,822 |
U. S. Treasury and agencies |  |  |
Investment securities available-for-sale |  |  |
Amortized Cost |  | 5,382 | 5,926
Unrealized Gains |  | 87 |
Unrealized Losses |  |  | (19)
Fair Value |  | 5,469 | 5,907
Obligations of state and political agencies |  |  |
Investment securities available-for-sale |  |  |
Amortized Cost |  |  | 148,491
Unrealized Gains |  |  | 5,282
Fair Value |  |  | 153,773
Amortized Cost |  | 145,172 |
Unrealized Gains |  | 1,530 |
Unrealized Losses |  | (29) |
Fair Value |  | 146,673 |
Fair value of debt securities available-for-sale transferred to held-to-maturity | $ 149,200 |  |
Net unrealized gain from available-for-sale to held-to-maturity | $ 1,300 |  |
Mortgage backed securities - Residential agency |  |  |
Investment securities available-for-sale |  |  |
Amortized Cost |  | 523,743 | 303,760
Unrealized Gains |  | 2,219 | 3,395
Unrealized Losses |  | (7,490) | (436)
Fair Value |  | 518,472 | 306,719
Amortized Cost |  | 217,414 |
Unrealized Gains |  | 55 |
Unrealized Losses |  | (602) |
Fair Value |  | 216,867 |
Mortgage backed securities - Commercial |  |  |
Investment securities available-for-sale |  |  |
Amortized Cost |  | 91,336 | 89,300
Unrealized Gains |  | 3,582 | 5,678
Fair Value |  | 94,918 | 94,978
Asset backed securities |  |  |
Investment securities available-for-sale |  |  |
Amortized Cost |  | 61 | 109
Unrealized Gains |  | 3 | 6
Fair Value |  | 64 | 115
Corporate bonds |  |  |
Investment securities available-for-sale |  |  |
Amortized Cost |  | 35,038 | 30,552
Unrealized Gains |  | 1,321 | 388
Unrealized Losses |  |  | (90)
Fair Value |  | $ 36,359 | $ 30,850

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