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MARKETABLE SECURITIES - Narrative (Details) | 3 Months Ended |
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Mar. 31, 2020 USD ($) Position security | Mar. 31, 2019 security | Dec. 31, 2019 USD ($)
Investments Debt And Equity Securities [Abstract] |  |  |
Allowance for credit losses for available for sale debt securities | $ 0 |  |
Other than temporary impairment losses on debt securities related to credit losses |  |  | $ 0
Number of investment positions in an unrealized loss position | Position | 66 |  |
Percentage of unrealized loss exceeds book value | 20.00% |  |
Number of securities other than agencies amount | security | 0 |  |
Fair value of securities pledged as collateral | $ 300,214,000 |  | $ 278,318,000
Number of securities sold | security | 0 | 0 |

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