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Benefit Plans (Narrative) (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
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 | $ 1,485 | $ 796 | $ 1,072
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement | 0 | 0 | (109)
Plan expenses | 965 | 885 | 805
Corporation self-funded medical plan | 100 |  |
Medical expenses | 2,895 | 2,281 | 3,026
Defined Benefit Plan Disclosure [Line Items] |  |  |
Performance Bonus Expense - Executive Plan | 103 | 53 | 252
Other Postretirement Benefits Plan [Member] |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Plan expenses | 529 | 345 | 251
Restricted Stock | Isabella Bank Corporation Restricted Stock Plan |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Compensation expense | 95 | $ 253 | $ 147
Unrecognized compensation expense | $ 88 |  |
Unrecognized compensation expense, period for recognition | 2 years 4 months 17 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 | 25.00% |  |
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 | 40.00% |  |
Safe Harbor 401(k) [Member] |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Vesting percentage | 100.00% |  |
Equity Collective Trust [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Investment allocation in securities | 50.00% |  |
Fixed Income Funds [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Investment allocation in securities | 50.00% |  |

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