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Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Thousands | Total | Cumulative effect of accounting change - adoption of ASC 326 | Isabella Bank Corporation Restricted Stock Plan | Common Stock | Common Stock Isabella Bank Corporation Restricted Stock Plan | Common Shares to be Issued for Deferred Compensation Obligations | Retained Earnings | Retained Earnings Cumulative effect of accounting change - adoption of ASC 326 | Accumulated Other Comprehensive Income (Loss)
--- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Beginning balance at Dec. 31, 2022 | $ 186,210 | $ (2,417) |  | $ 128,651 |  | $ 5,005 | $ 89,748 | $ (2,417) | $ (37,194)
Beginning balances (in shares) at Dec. 31, 2022 |  |  |  | 7,559,421 |  |  |  |  |
Increase (Decrease) in Stockholders' Equity [Roll Forward] |  |  |  |  |  |  |  |  |
Comprehensive income (loss) | 29,465 |  |  |  |  |  | 18,167 |  | 11,298
Issuance of common stock | 1,617 |  |  | $ 1,617 |  |  |  |  |
Issuance of common stock, shares |  |  |  | 75,488 |  |  |  |  |
Common stock transferred from the Rabbi Trust to satisfy deferred compensation obligations | 0 |  |  | $ 1,841 |  | (1,841) |  |  |
Share-based payment awards under the Directors Plan | 529 |  |  |  |  | 529 |  |  |
Share-based compensation expense recognized in earnings under the RSP |  |  | $ 253 |  | $ 253 |  |  |  |
Common stock purchased for deferred compensation obligations | (1,624) |  |  | (1,624) |  |  |  |  |
Common stock repurchased | (3,415) |  |  | $ (3,415) |  |  |  |  |
Common stock repurchased (in shares) |  |  |  | (149,020) |  |  |  |  |
Cash dividends paid | (8,216) |  |  |  |  |  | (8,216) |  |
Ending balance at Dec. 31, 2023 | 202,402 |  |  | $ 127,323 |  | 3,693 | 97,282 |  | (25,896)
Ending balances (in shares) at Dec. 31, 2023 |  |  |  | 7,485,889 |  |  |  |  |
Increase (Decrease) in Stockholders' Equity [Roll Forward] |  |  |  |  |  |  |  |  |
Comprehensive income (loss) | 18,430 |  |  |  |  |  | 13,889 |  | 4,541
Issuance of common stock | 1,523 |  |  | $ 1,523 |  |  |  |  |
Issuance of common stock, shares |  |  |  | 75,341 |  |  |  |  |
Common stock transferred from the Rabbi Trust to satisfy deferred compensation obligations | 0 |  |  | $ 1,691 |  | (1,691) |  |  |
Share-based payment awards under the Directors Plan | 381 |  |  |  |  | 381 |  |  |
Share-based compensation expense recognized in earnings under the RSP |  |  | 95 |  | $ 95 |  |  |  |
Common stock purchased for deferred compensation obligations | (1,332) |  |  | (1,332) |  |  |  |  |
Common stock repurchased | (3,076) |  |  | $ (3,076) |  |  |  |  |
Common stock repurchased (in shares) |  |  |  | (152,577) |  |  |  |  |
Common stock issued for deferred compensation under the RSP (in shares) |  |  |  |  | 16,240 |  |  |  |
Cash dividends paid | (8,147) |  |  |  |  |  | (8,147) |  |
Ending balance at Dec. 31, 2024 | $ 210,276 |  |  | $ 126,224 |  | 2,383 | 103,024 |  | (21,355)
Ending balances (in shares) at Dec. 31, 2024 | 7,424,893 |  |  | 7,424,893 |  |  |  |  |
Increase (Decrease) in Stockholders' Equity [Roll Forward] |  |  |  |  |  |  |  |  |
Comprehensive income (loss) | $ 32,242 |  |  |  |  |  | 18,910 |  | 13,332
Issuance of common stock | 1,331 |  |  | $ 1,331 |  |  |  |  |
Issuance of common stock, shares |  |  |  | 42,904 |  |  |  |  |
Common stock transferred from the Rabbi Trust to satisfy deferred compensation obligations | 0 |  |  | $ 294 |  | (294) |  |  |
Share-based payment awards under the Directors Plan | 277 |  |  |  |  | 277 |  |  |
Share-based compensation expense recognized in earnings under the RSP |  |  | $ 64 |  | $ 64 |  |  |  |
Common stock repurchased | (4,709) |  |  | $ (4,709) |  |  |  |  |
Common stock repurchased (in shares) |  |  |  | (156,957) |  |  |  |  |
Common stock issued for deferred compensation under the RSP (in shares) |  |  |  |  | 11,367 |  |  |  |
Cash dividends paid | (8,085) |  |  |  |  |  | (8,085) |  |
Ending balance at Dec. 31, 2025 | $ 231,396 |  |  | $ 123,204 |  | $ 2,366 | $ 113,849 |  | $ (8,023)
Ending balances (in shares) at Dec. 31, 2025 | 7,322,207 |  |  | 7,322,207 |  |  |  |  |

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