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Securities, Held to Maturity (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Held-to-maturity securities, fair value to amortized cost [Abstract] |  |  |
Amortized cost | $ 630,074 | $ 783,599 |
Unrealized gains | 11,817 | 3,362 |
Unrealized losses | 629 | 8,286 |
Estimated fair value | 641,262 | 778,675 |
Transactions of HTM securities [Abstract] |  |  |
Held-to-maturity securities sold, amortized cost | 0 | 0 | $ 800
Held-to-maturity securities sold, realized loss |  |  | (2)
Held-to-maturity securities sold, unrealized loss |  |  | (2)
Gains from calls on HTM securities | 12 | 0 | $ 0
Federal Agency [Member] |  |  |
Held-to-maturity securities, fair value to amortized cost [Abstract] |  |  |
Amortized cost |  | 19,995 |
Unrealized gains |  | 52 |
Unrealized losses |  | 0 |
Estimated fair value |  | 20,047 |
Mortgage-backed Securities, Government-Sponsored Enterprises [Member] |  |  |
Held-to-maturity securities, fair value to amortized cost [Abstract] |  |  |
Amortized cost | 149,448 | 164,618 |
Unrealized gains | 3,184 | 712 |
Unrealized losses | 155 | 2,773 |
Estimated fair value | 152,477 | 162,557 |
Mortgage-Backed, U.S. Government Agency Securities [Member] |  |  |
Held-to-maturity securities, fair value to amortized cost [Abstract] |  |  |
Amortized cost | 13,667 | 15,230 |
Unrealized gains | 584 | 403 |
Unrealized losses | 0 | 0 |
Estimated fair value | 14,251 | 15,633 |
Collateralized Mortgage Obligations, Government-Sponsored Enterprises [Member] |  |  |
Held-to-maturity securities, fair value to amortized cost [Abstract] |  |  |
Amortized cost | 189,402 | 257,475 |
Unrealized gains | 2,165 | 1,097 |
Unrealized losses | 368 | 3,897 |
Estimated fair value | 191,199 | 254,675 |
Collateralized Mortgage Obligations, U.S. Government Agency Securities [Member] |  |  |
Held-to-maturity securities, fair value to amortized cost [Abstract] |  |  |
Amortized cost | 110,498 | 83,148 |
Unrealized gains | 3,256 | 767 |
Unrealized losses | 100 | 0 |
Estimated fair value | 113,654 | 83,915 |
State & Municipal [Member] |  |  |
Held-to-maturity securities, fair value to amortized cost [Abstract] |  |  |
Amortized cost | 167,059 | 243,133 |
Unrealized gains | 2,628 | 331 |
Unrealized losses | 6 | 1,616 |
Estimated fair value | 169,681 | 241,848 |
Public Deposits and Other Purposes [Member] |  |  |
Securities pledged [Abstract] |  |  |
Amortized costs of securities available for sale and held to maturity pledged | 1,300,000 | 1,500,000 |
Securities Sold under Repurchase Agreements [Member] |  |  |
Securities pledged [Abstract] |  |  |
Amortized costs of securities available for sale and held to maturity pledged | $ 189,800 | $ 215,300 |

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