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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Stock-based compensation (Details) - USD ($) | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019
Restricted Stock |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Number of shares authorized (in shares) | 15,000 |
Age limit for forfeiture of stock award | 65 years |
Restricted Stock | Share-based Compensation Award, Vesting Each Year Commencing with First Anniversary Date of Award |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Award vesting rights percent | 20.00% |
Restricted Stock | Share-based Compensation Award, Vesting on Fifth Anniversary Date |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Award vesting rights percent | 100.00% |
Incentive Compensation Plan |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Number of shares authorized (in shares) | 10,000 |
Cash compensation | $ 300,000 |
Director |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Increase in annual cash retainer paid |  | $ 6,000
Annual cash retainer paid to individuals |  | 11,500
Director | Directors' Compensation Plan |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Number of shares authorized (in shares) | 20,000 |
Award requisite service period (months) | 12 months |
Trading days period | 30 days |
Board of Directors Chairman |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Annual cash retainer paid to individuals |  | 19,250
Audit Committee Chairman |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Increase in annual cash retainer paid |  | 2,875
Annual cash retainer paid to individuals |  | $ 14,375
Deferred Compensation, Share-based Payments |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Maximum annual installments period (years) | 10 years |

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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