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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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Share-based Compensation Arrangement by Share-based Payment Award, Percentage of Employee Annual Salary

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