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Benefit Plans (Narrative) (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Retirement Benefits [Abstract] |  |  |
Employees contribution | 100.00% |  |
Corporation matching contribution, percent | 100.00% |  |
Employee contribution, percent | 5.00% |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Performance bonus expense | $ 796 | $ 1,072 | $ 1,063
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement | 0 | (109) | 0
Plan expenses | 885 | 805 | 792
Accumulated other comprehensive income includes net unrecognized pension cost before income taxes | 882 |  |
Corporation self-funded medical plan | 100 |  |
Medical expenses | 2,281 | 3,026 | 3,297
Defined Benefit Plan Disclosure [Line Items] |  |  |
Performance Bonus Expense - Executive Plan | 53 | 252 | 253
Other Postretirement Benefits Plan [Member] |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Plan expenses | 345 | 251 | 352
Restricted Stock | Isabella Bank Corporation Restricted Stock Plan |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Compensation expense | 253 | $ 147 | $ 86
Unrecognized compensation expense | $ 92 |  |
Unrecognized compensation expense, period for recognition | 1 year 6 months 18 days |  |
Minimum [Member] | Restricted Stock | Isabella Bank Corporation Restricted Stock Plan |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Award as a percentage of salary | 2500.00% |  |
Maximum [Member] | Restricted Stock | Isabella Bank Corporation Restricted Stock Plan |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Award as a percentage of salary | 4000.00% |  |
Safe Harbor 401(k) [Member] |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Vesting percentage | 100.00% |  |
Fixed Income Funds [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Investment allocation in securities | 50.00% |  |
Equity Collective Trust [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Investment allocation in securities | 50.00% |  |

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