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Benefit Plans - Nonvested Restricted Stock Awards Activity (Details) - Restricted Stock - Isabella Bank Corporation Restricted Stock Plan - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024
Number of Shares
Beginning balance (in shares)	14,733	27,072
Granted (in shares)	6,125	3,901
Vested (in shares)	(8,023)	(16,240)
Forfeited (in shares)	0	0
Ending balance (in shares)	12,835	14,733
Fair Value
Beginning balance	$ 323	$ 592
Granted	144	76
Vested	(173)	(345)
Forfeited	0	0
Ending balance	$ 294	$ 323

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Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value

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The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(03)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

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- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
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-Name Accounting Standards Codification
-Section 50
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-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
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-Name Accounting Standards Codification
-Section 50
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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
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-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

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Intrinsic value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-4

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