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Related Party Transactions (Narrative) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Employee Stock Ownership Plan (ESOP) Deposit [Member] | Subsidiaries [Member]
Related Party Transaction [Line Items]
Total deposits	$ 0	$ 266
Principal Officers and Directors and Their Affiliates [Member]
Related Party Transaction [Line Items]
Total deposits	$ 5,029	$ 5,671
Affiliated Entity [Member] | Isabella Bank Foundation [Member]
Related Party Transaction [Line Items]
Common Stock, Shares Held by Related Party	44,350	44,350

X

- Definition

Common Stock, Shares Held by Related Party

+ References

No definition available.

+ Details

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Namespace Prefix:	isba_
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Balance Type:	na
Period Type:	instant

X

- Definition

Amount of deposits held by the entity for a related party (entity, shareholder, employee).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(k))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

+ Details

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X

- 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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- Details

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- Details

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- Details

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- Details

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