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Investment Securities - Gross unrealized losses (Details) - USD ($) $ in Thousands | Sep. 30, 2023 | Dec. 31, 2022
--- | --- | ---
Investment securities available-for-sale |  |
Unrealized losses less than 12 months | $ (9) | $ (19,761)
Fair value less than 12 months | 584 | 178,719
Unrealized losses over 12 months | (156,025) | (112,503)
Fair value over 12 months | 600,544 | 535,024
Total Unrealized losses | (156,034) | (132,264)
Total Fair value | 601,128 | 713,743
Held-to-maturity investment securities |  |
Unrealized losses less than 12 months |  | (3,336)
Fair value less than 12 months |  | 18,788
Unrealized losses over 12 months |  | (47,654)
Fair value over 12 months |  | 249,623
Total Unrealized losses |  | (50,990)
Total Fair value |  | 268,411
Unrealized losses less than 12 months |  | (23,097)
Fair value less than 12 months |  | 197,507
Unrealized losses over 12 months |  | (160,157)
Fair value over 12 months |  | 784,647
Total Unrealized losses |  | (183,254)
Total Fair value |  | 982,154
U. S. Treasury and agencies |  |
Investment securities available-for-sale |  |
Unrealized losses less than 12 months |  | (17)
Fair value less than 12 months |  | 509
Unrealized losses over 12 months | (23) |
Fair value over 12 months | 389 |
Total Unrealized losses | (23) | (17)
Total Fair value | 389 | 509
Mortgage backed securities - Residential agency |  |
Investment securities available-for-sale |  |
Unrealized losses less than 12 months | (9) | (10,457)
Fair value less than 12 months | 577 | 79,693
Unrealized losses over 12 months | (135,213) | (107,711)
Fair value over 12 months | 484,451 | 507,418
Total Unrealized losses | (135,222) | (118,168)
Total Fair value | 485,028 | 587,111
Held-to-maturity investment securities |  |
Unrealized losses over 12 months |  | (33,254)
Fair value over 12 months |  | 150,861
Total Unrealized losses |  | (33,254)
Total Fair value |  | 150,861
Mortgage backed securities - Commercial |  |
Investment securities available-for-sale |  |
Unrealized losses less than 12 months |  | (4,835)
Fair value less than 12 months |  | 50,437
Unrealized losses over 12 months | (8,295) | (2,276)
Fair value over 12 months | 58,684 | 13,120
Total Unrealized losses | (8,295) | (7,111)
Total Fair value | 58,684 | 63,557
Asset backed securities |  |
Investment securities available-for-sale |  |
Fair value less than 12 months | 7 | 32
Fair value over 12 months | 19 | 2
Total Fair value | 26 | 34
Corporate bonds |  |
Investment securities available-for-sale |  |
Unrealized losses less than 12 months |  | (4,452)
Fair value less than 12 months |  | 48,048
Unrealized losses over 12 months | (12,494) | (2,516)
Fair value over 12 months | 57,001 | 14,484
Total Unrealized losses | (12,494) | (6,968)
Total Fair value | $ 57,001 | 62,532
Obligations of state and political agencies. |  |
Held-to-maturity investment securities |  |
Unrealized losses less than 12 months |  | (3,336)
Fair value less than 12 months |  | 18,788
Unrealized losses over 12 months |  | (14,400)
Fair value over 12 months |  | 98,762
Total Unrealized losses |  | (17,736)
Total Fair value |  | $ 117,550

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