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Restricted Stock Plan (Details) - Restricted Stock - Isabella Bank Corporation Restricted Stock Plan - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended |  |
--- | --- | --- | --- | ---
Sep. 30, 2021 | Sep. 30, 2021 | Jun. 30, 2021 | Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Share-based Payment Arrangement, Expense | $ 33 | $ 58 |  |
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount | $ 346 | $ 346 |  |
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition |  | 2 years 11 months 12 days |  |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number | 20,123 | 20,123 | 16,257 | 4,658
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Nonvested | $ 418 | $ 418 | $ 334 | $ 82
Shares Granted, Value, Share-based Payment Arrangement, before Forfeiture | 84 | 336 |  |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Intrinsic Value, Amount Per Share | 0 | 0 |  |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Vested | $ 0 | $ 0 |  |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | 3,866 | 15,465 |  |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period | 0 | 0 |  |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period | 0 | 0 |  |
Minimum [Member] |  |  |  |
Share-based Payment Arrangement [Abstract] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Percentage of Employee Annual Salary | 2500.00% | 2500.00% |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Percentage of Employee Annual Salary | 2500.00% | 2500.00% |  |
Maximum [Member] |  |  |  |
Share-based Payment Arrangement [Abstract] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Percentage of Employee Annual Salary | 4000.00% | 4000.00% |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Percentage of Employee Annual Salary | 4000.00% | 4000.00% |  |

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