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FAIR VALUE - Quantitative Information (Details) - Significant Unobservable Inputs (Level 3) - Other real estate owned: - Non-recurring - USD ($) $ in Thousands | 9 Months Ended | 12 Months Ended
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Sep. 30, 2021 | Dec. 31, 2020
Information related to Level 3 non-recurring fair value measurement [Abstract] |  |
Assets, fair value disclosure | $ 171 | $ 237
Residential mortgages | Sales comparison |  |
Information related to Level 3 non-recurring fair value measurement [Abstract] |  |
Assets, fair value disclosure | $ 124 | $ 126
Residential mortgages | Sales comparison | Minimum |  |
Information related to Level 3 non-recurring fair value measurement [Abstract] |  |
Discount to appraised value (in percentage) | 20.80% | 20.80%
Residential mortgages | Sales comparison | Maximum |  |
Information related to Level 3 non-recurring fair value measurement [Abstract] |  |
Discount to appraised value (in percentage) | 20.80% | 20.80%
Residential mortgages | Sales comparison | Weighted Average |  |
Information related to Level 3 non-recurring fair value measurement [Abstract] |  |
Discount to appraised value (in percentage) | 20.80% | 20.80%
Home equity lines and loans | Sales comparison |  |
Information related to Level 3 non-recurring fair value measurement [Abstract] |  |
Assets, fair value disclosure | $ 47 |
Home equity lines and loans | Sales comparison | Minimum |  |
Information related to Level 3 non-recurring fair value measurement [Abstract] |  |
Discount to appraised value (in percentage) | 10.00% |
Home equity lines and loans | Sales comparison | Maximum |  |
Information related to Level 3 non-recurring fair value measurement [Abstract] |  |
Discount to appraised value (in percentage) | 10.00% |
Home equity lines and loans | Sales comparison | Weighted Average |  |
Information related to Level 3 non-recurring fair value measurement [Abstract] |  |
Discount to appraised value (in percentage) | 10.00% |
Commercial mortgages, other | Sales comparison |  |
Information related to Level 3 non-recurring fair value measurement [Abstract] |  |
Assets, fair value disclosure |  | $ 111
Commercial mortgages, other | Sales comparison | Minimum |  |
Information related to Level 3 non-recurring fair value measurement [Abstract] |  |
Discount to appraised value (in percentage) |  | 20.80%
Commercial mortgages, other | Sales comparison | Maximum |  |
Information related to Level 3 non-recurring fair value measurement [Abstract] |  |
Discount to appraised value (in percentage) |  | 20.80%
Commercial mortgages, other | Sales comparison | Weighted Average |  |
Information related to Level 3 non-recurring fair value measurement [Abstract] |  |
Discount to appraised value (in percentage) |  | 20.80%

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- Definition Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=123874694&loc=d3e19207-110258 + Details
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