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SECURITIES - Summary of Held to Maturity Investment Securities (Details) - USD ($) $ in Thousands | Dec. 31, 2020 | Dec. 31, 2019
--- | --- | ---
Held to maturity: |  |
Amortized Cost | $ 85,700 | $ 133,638
Gross Unrealized Gains | 3,634 | 1,731
Gross Unrealized Losses | (9) | (342)
Estimated Fair Value | 89,325 | 135,027
State and municipal obligations |  |
Held to maturity: |  |
Amortized Cost | 23,715 | 41,008
Gross Unrealized Gains | 1,406 | 809
Estimated Fair Value | 25,121 | 41,817
U.S. GSE residential mortgage-backed securities |  |
Held to maturity: |  |
Amortized Cost | 6,272 | 8,142
Gross Unrealized Gains | 227 | 5
Gross Unrealized Losses |  | (54)
Estimated Fair Value | 6,499 | 8,093
U.S. GSE residential collateralized mortgage obligations |  |
Held to maturity: |  |
Amortized Cost | 18,511 | 39,936
Gross Unrealized Gains | 489 | 624
Gross Unrealized Losses | (9) | (62)
Estimated Fair Value | 18,991 | 40,498
U.S. GSE commercial mortgage-backed securities |  |
Held to maturity: |  |
Amortized Cost | 13,069 | 17,215
Gross Unrealized Gains | 625 | 102
Gross Unrealized Losses |  | (82)
Estimated Fair Value | 13,694 | 17,235
U.S. GSE commercial collateralized mortgage obligations |  |
Held to maturity: |  |
Amortized Cost | 24,133 | 27,337
Gross Unrealized Gains | 887 | 191
Gross Unrealized Losses |  | (144)
Estimated Fair Value | $ 25,020 | $ 27,384

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