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SECURITIES (Narrative) (Details) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2020 USD ($) security | Dec. 31, 2019 USD ($) security
Schedule of Investments [Line Items] |  |
Available for sale securities that had been in a continuous loss position for more than 12 months | $ 36,400,000 | $ 75,000,000.0
Available-for-sale securities, continuous unrealized loss position, 12 months or longer, accumulated loss | 1,042,000 | 696,000
Securities available for sale, at fair value | 1,972,903,000 | $ 1,945,445,000
Available for sale securities past due or non-accrual | 0 |
HTM securities, additional reserve for allowance for credit losses | 0 |
Held to maturity securities, past due | $ 0 |
Federal Home Loan Bank requires Bank to maintain percentage of stock equal to outstanding borrowings | 4.25% | 4.25%
Percentage of Federal Reserve Bank of Richmond reserve | 6.00% | 6.00%
Restricted equity securities consist of Federal Reserve Bank stock | $ 67,000,000.0 | $ 67,000,000.0
Federal Home Loan Bank Stock | $ 63,200,000 | $ 63,900,000
Available-for-sale Securities |  |
Schedule of Investments [Line Items] |  |
Available for sale securities that had been in a continuous loss position for more than 12 months, Number of issues | security | 20 | 47
Non-agency collateralized mortgage obligations | AAA |  |
Schedule of Investments [Line Items] |  |
Securities available for sale, at fair value | $ 40,600,000 |
Securities available for sale, unrealized losses | $ 1,300,000 |
Percentage of Simplified Supervisory Formula Approach (SSFA) rating | 20.00% |

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