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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) |  |  | 3 Months Ended | 9 Months Ended |  |
--- | --- | --- | --- | --- | --- | ---
Mar. 16, 2020 | Jan. 01, 2020 USD ($) | Sep. 30, 2020 USD ($) subsidary Family Residentialhouse | Sep. 30, 2019 USD ($) | Sep. 30, 2020 USD ($) subsidary Family Residentialhouse | Sep. 30, 2019 USD ($) | Mar. 27, 2020 USD ($) | Dec. 31, 2019 USD ($)
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |
Number of subsidiaries | subsidary |  |  | 6 |  | 6 |  |  |
Provision for loan losses |  |  | $ (300,000) | $ 100,000 | $ 13,200,000 | $ 1,250,000 |  |
Decrease to retained earnings |  |  | $ 105,721,000 |  | 105,721,000 |  |  | $ 98,239,000
Retained earnings, net of tax |  |  |  |  | $ 955,000 |  |  |
Number of families secured by loans of real estate | Family |  |  | 4 |  | 4 |  |  |
Number of housing units secured by loans from segment | Residentialhouse |  |  | 5 |  | 5 |  |  |
Paycheck Protection Program Loans |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |
Percentage of government guaranteed loans |  |  | 100.00% |  | 100.00% |  |  |
ASU 2017-04 |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |
Change in Accounting Principle, Accounting Standards Update, Adopted [true false] |  |  | true |  | true |  |  |
Change in Accounting Principle, Accounting Standards Update, Adoption Date |  |  | Jan. 01, 2020 |  | Jan. 01, 2020 |  |  |
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false] |  |  | true |  | true |  |  |
Accounting Standards Update 2016-13 |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |
Change in Accounting Principle, Accounting Standards Update, Adopted [true false] |  |  | true |  | true |  |  |
Change in Accounting Principle, Accounting Standards Update, Adoption Date |  |  | Jan. 01, 2020 |  | Jan. 01, 2020 |  |  |
Increase to allowance for credit losses |  | $ 4,548,000 |  |  |  |  |  |
Increase to allowance for credit losses, percent |  | 28.10% |  |  |  |  |  |
Provision for loan losses |  |  | $ 13,200,000 |  | $ 13,200,000 |  |  |
Accounting Standards Update 2016-13 | Cumulative Effect | Revision of Prior Period, Adjustment |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |
Decrease to retained earnings |  |  | $ (3,593,000) |  | (3,593,000) |  |  |
Retained earnings, net of tax |  |  |  |  | $ 955,000 |  |  |
COVID-19 |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |
Maximum authorized amount of coronavirus aid, relief and economic security |  |  |  |  |  |  | $ 2,000,000,000,000 |
Description of federal fund interest rate |  |  |  |  | Due to the COVID-19 pandemic, market interest rates have declined significantly, with the 10-year Treasury bond falling below 1.00% on March 3, 2020 for the first time. On March 16, 2020, the Federal Open Market Committee reduced the target federal funds rate range to 0.00% to 0.25%. |  |  |
COVID-19 | Minimum |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |
Federal open market committee reduced target federal funds interest rate. | 0.00% |  |  |  |  |  |  |
COVID-19 | Maximum |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |
Federal open market committee reduced target federal funds interest rate. | 0.25% |  |  |  |  |  |  |

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