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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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