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Related Party Transactions (Ending balances of, and contributions to the Isabella Bank Foundation) (Details) - USD ($) $ in Thousands | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
--- | --- | --- | ---
Related Party Transaction [Line Items] |  |  |
Ending assets | $ 1,957,378 | $ 1,812,643 |
Affiliated Entity [Member] | Isabella Bank Foundation [Member] |  |  |
Related Party Transaction [Line Items] |  |  |
Common Stock, Shares Held by Related Party | 44,350 | 44,350 |
Affiliated Entity [Member] | Isabella Bank Foundation [Member] |  |  |
Related Party Transaction [Line Items] |  |  |
Ending assets | $ 1,286 | $ 1,678 | $ 1,731
Donations | $ 0 | $ 50 | $ 0

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Balance Type: | debit
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- Definition Common Stock, Shares Held by Related Party + References No definition available. + Details
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Balance Type: | na
Period Type: | instant

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- Definition Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(11)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 22 -URI http://asc.fasb.org/extlink&oid=115929826&loc=d3e8736-108599 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(12)) -URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Details
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Namespace Prefix: |
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Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
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Balance Type: |
Period Type: |

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- Details
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