Related Party Transactions (Ending balances of, and contributions to the Isabella Bank Foundation) (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Related Party Transaction [Line Items]
Ending assets	$ 2,032,158	$ 1,957,378
Affiliated Entity [Member] \| Isabella Bank Foundation [Member]
Related Party Transaction [Line Items]
Common Stock, Shares Held by Related Party	20,000	44,350
Affiliated Entity [Member] \| Isabella Bank Foundation [Member]
Related Party Transaction [Line Items]
Ending assets	$ 1,511	$ 1,286	$ 1,678
Donations	$ 50	$ 0	$ 50

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.

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+ Details