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Related Party Transactions - Narrative (Details) - USD ($) $ in Thousands	Dec. 31, 2025	Dec. 31, 2024
Principal Officers and Directors and Their Affiliates
Related Party Transaction [Line Items]
Total deposits	$ 5,050	$ 4,024
Affiliated Entity | Isabella Bank Foundation
Related Party Transaction [Line Items]
Common stock, shares held by related party	20,000	20,000

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