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Securities, Held to Maturity (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2021 | Sep. 30, 2020 | Dec. 31, 2020
Held-to-maturity securities, fair value to amortized cost [Abstract] |  |  |  |  |
Amortized cost | $ 683,103 |  | $ 683,103 |  | $ 616,560
Unrealized gains | 12,260 |  | 12,260 |  | 21,942
Unrealized losses | 6,234 |  | 6,234 |  | 1,675
Estimated fair value | 689,129 |  | 689,129 |  | 636,827
Allowance for credit losses on HTM securities | 0 |  | 0 |  | 0
Gains from calls on HTM securities | 14 | $ 11 | 29 | $ 15 |
Held-to-maturity securities sold, amortized cost | 0 |  | 0 | 1,000 |
Held-to-maturity securities sold, realized loss |  |  |  | $ 1 |
Amortized costs of securities available for sale and held to maturity pledged | 1,600,000 |  | 1,600,000 |  | 1,400,000
Amortized costs of securities AFS and HTM pledged as collateral for repurchase agreements | 149,200 |  | 149,200 |  | 305,200
Federal Agency [Member] |  |  |  |  |
Held-to-maturity securities, fair value to amortized cost [Abstract] |  |  |  |  |
Amortized cost | 100,000 |  | 100,000 |  | 100,000
Unrealized gains | 0 |  | 0 |  | 0
Unrealized losses | 3,821 |  | 3,821 |  | 1,658
Estimated fair value | 96,179 |  | 96,179 |  | 98,342
Mortgage-Backed, Government Sponsored Enterprises [Member] |  |  |  |  |
Held-to-maturity securities, fair value to amortized cost [Abstract] |  |  |  |  |
Amortized cost | 121,040 |  | 121,040 |  | 107,914
Unrealized gains | 2,851 |  | 2,851 |  | 4,583
Unrealized losses | 568 |  | 568 |  | 0
Estimated fair value | 123,323 |  | 123,323 |  | 112,497
Mortgage-Backed, U.S. Government Agency Securities [Member] |  |  |  |  |
Held-to-maturity securities, fair value to amortized cost [Abstract] |  |  |  |  |
Amortized cost | 9,121 |  | 9,121 |  | 11,533
Unrealized gains | 659 |  | 659 |  | 979
Unrealized losses | 0 |  | 0 |  | 0
Estimated fair value | 9,780 |  | 9,780 |  | 12,512
Collateralized Mortgage Obligations, Government-Sponsored Enterprises [Member] |  |  |  |  |
Held-to-maturity securities, fair value to amortized cost [Abstract] |  |  |  |  |
Amortized cost | 75,852 |  | 75,852 |  | 103,105
Unrealized gains | 3,050 |  | 3,050 |  | 4,477
Unrealized losses | 0 |  | 0 |  | 0
Estimated fair value | 78,902 |  | 78,902 |  | 107,582
Collateralized Mortgage Obligations, U.S. Government Agency Securities [Member] |  |  |  |  |
Held-to-maturity securities, fair value to amortized cost [Abstract] |  |  |  |  |
Amortized cost | 54,587 |  | 54,587 |  | 79,145
Unrealized gains | 679 |  | 679 |  | 3,950
Unrealized losses | 341 |  | 341 |  | 0
Estimated fair value | 54,925 |  | 54,925 |  | 83,095
State & Municipal [Member] |  |  |  |  |
Held-to-maturity securities, fair value to amortized cost [Abstract] |  |  |  |  |
Amortized cost | 322,503 |  | 322,503 |  | 214,863
Unrealized gains | 5,021 |  | 5,021 |  | 7,953
Unrealized losses | 1,504 |  | 1,504 |  | 17
Estimated fair value | $ 326,020 |  | $ 326,020 |  | $ 222,799

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