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Restricted Stock Plan (Narrative) (Details) - Restricted Stock - Isabella Bank Corporation Restricted Stock Plan - USD ($) $ in Thousands | 3 Months Ended
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Mar. 31, 2023 | Mar. 31, 2022
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Share-based Payment Arrangement, Expense | $ 42 | $ 31
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition | 2 years 10 months 9 days |
Share-based Payment Arrangement, Nonvested Award, Excluding Option, Cost Not yet Recognized, Amount | $ 394 |
Minimum [Member] |  |
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% |
Maximum [Member] |  |
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% |

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- Definition Amount of expense for award under share-based payment arrangement. Excludes amount capitalized. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1)(i) -URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901 + Details
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- Definition Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (i) -URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901 + Details
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- Definition Amount of cost to be recognized for nonvested award under share-based payment arrangement. Excludes share and unit options. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (i) -URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901 + Details
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