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MARKETABLE SECURITIES - Narrative (Details) | 12 Months Ended
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Dec. 31, 2019 USD ($) security | Dec. 31, 2018 USD ($) security | Dec. 31, 2017 USD ($) security
Debt Securities, Available-for-sale [Line Items] |  |  |
Other than temporary impairment losses on debt securities related to credit losses | $ | $ 0 | $ 0 |
Securities in unrealized loss positions, over 12 months | 95 |  |
Securities in unrealized loss positions, less than 12 months | 75 |  |
Available-for-sale, securities in unrealized loss positions, over 12 months | 37 |  |
Held-to-maturity, securities in unrealized loss positions, over 12 months | 58 |  |
Available-for-sale securities in unrealized loss positions, less than 12 months | 13 |  |
Held-to-maturity, securities in unrealized loss positions, less than 12 months | 62 |  |
Number of securities other than agencies amount | 0 |  |
Fair value of securities pledged as collateral | $ | $ 278,318,000 | $ 259,557,000 |
Number of held-to-maturity securities sold | 0 | 0 | 3
Amortized cost, other than temporary impairment | $ |  |  | $ 324,000
Amortized cost, principal write-downs | $ |  |  | $ 499,000
Municipal securities |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Number of held-to-maturity securities sold |  |  | 2
Corporate bonds |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Number of held-to-maturity securities sold |  |  | 3

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