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INVESTMENT SECURITIES - Narrative (Details) - USD ($) | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2021 | Sep. 30, 2020 | Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Held-to-maturity securities, unrealized loss position | $ 0 |  | $ 0 |  | $ 0
Tax exempt interest income on available-for-sale securities | $ 2,600,000 | $ 2,800,000 | $ 7,600,000 | $ 7,900,000 |
Mortgage Backed Securities and Collateralized Mortgage Obligations |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Weighted average yield | 1.85% |  | 1.85% |  | 1.92%

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