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MARKETABLE SECURITIES - Narrative (Details) | 12 Months Ended |
--- | --- | ---
Dec. 31, 2017 USD ($) security | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($) | Dec. 31, 2013 USD ($)
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Carrying value | $ 174,684,000 | $ 189,371,000 |  |
Unrealized losses | 448,000 | 4,700,000 |  |
Other than temporary impairment losses on debt securities related to credit losses | $ 0 | 0 |  |
Securities in unrealized loss positions, over 12 months | security | 62 |  |  |
Securities in unrealized loss positions, less than 12 months | security | 36 |  |  |
Available-for-sale, securities in unrealized loss positions, over 12 months | security | 17 |  |  |
Held-to-maturity, securities in unrealized loss positions, over 12 months | security | 45 |  |  |
Available-for-sale securities in unrealized loss positions, less than 12 months | security | 20 |  |  |
Held-to-maturity, securities in unrealized loss positions, less than 12 months | security | 16 |  |  |
Fair value of securities pledged as collateral | $ 245,600,000 | 259,499,000 |  |
Number of held-to-maturity securities sold | security | 5 |  |  |
Amortized cost | $ 3,140,000 | 1,842,000 | $ 0 |
Non-Agency Collateralized Mortgage Obligations |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Carrying value |  | 1,636,000 |  |
Unrealized losses |  | $ 521,000 |  |
Other than temporary impairment losses on debt securities related to credit losses |  |  |  | $ 324,000
Municipal securities |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Number of held-to-maturity securities sold | security | 3 |  |  |
Corporate bonds |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Number of held-to-maturity securities sold | security | 2 |  |  |
Other Than Temporary Impairment |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized cost | $ 324,000 |  |  |
Principal Write-downs |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized cost | $ 499,000 |  |  |

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