v3.26.1
Capital Ratios and Shareholders' Equity - Compliance with Regulatory Capital Requirements (Details)
$ in Thousands
Jun. 30, 2026
USD ($)
Dec. 31, 2025
USD ($)
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]    
Common equity Tier 1 capital to risk weighted assets, Actual, Amount $ 209,173 $ 191,137
Common equity Tier 1 capital to risk weighted assets, Actual, Ratio 0.1234 0.1173
Common equity Tier 1 capital to risk weighted assets, Minimum Capital Required Plus Capital Conservation Buffer, Amount $ 118,619 $ 114,114
Common equity Tier 1 capital to risk weighted assets, Minimum Capital Required Plus Capital Conservation Buffer, Ratio 7.00% 7.00%
Tier 1 capital to risk weighted assets, Actual, Amount $ 209,173 $ 191,137
Tier 1 capital to risk weighted assets, Actual, Ratio 0.1234 0.1173
Tier 1 capital to risk weighted assets, Minimum Capital Required Plus Capital Conservation Buffer, Amount $ 144,037 $ 138,568
Tier 1 capital to risk weighted assets, Minimum Capital Required Plus Capital Conservation Buffer, Ratio 0.0850 0.0850
Total capital to risk weighted assets, Actual, Amount $ 247,903 $ 234,871
Total capital to risk weighted assets, Actual, Ratio 0.1463 0.1441
Total capital to risk weighted assets, Minimum Capital Required Plus Capital Conservation Buffer, Amount $ 177,928 $ 171,172
Total capital to risk weighted assets, Minimum Capital Required Plus Capital Conservation Buffer, Ratio 0.1050 0.1050
Tier 1 capital to average assets, Actual, Amount $ 209,173 $ 191,137
Tier 1 capital to average assets, Actual, Ratio 0.0959 0.0884
Tier 1 capital to average assets, Minimum Capital Required Plus Capital Conservation Buffer, Amount $ 87,235 $ 86,476
Tier 1 capital to average assets, Minimum Capital Required Plus Capital Conservation Buffer, Ratio 0.0400 0.0400
Isabella Bank    
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]    
Common equity Tier 1 capital to risk weighted assets, Actual, Amount $ 194,064 $ 182,116
Common equity Tier 1 capital to risk weighted assets, Actual, Ratio 0.1149 0.1120
Common equity Tier 1 capital to risk weighted assets, Minimum Capital Required Plus Capital Conservation Buffer, Amount $ 118,197 $ 113,783
Common equity Tier 1 capital to risk weighted assets, Minimum Capital Required Plus Capital Conservation Buffer, Ratio 7.00% 7.00%
Common equity Tier 1 capital to risk weighted assets, Minimum Capital Required To Be Considered Well Capitalized, Amount $ 109,754 $ 105,656
Common equity Tier 1 capital to risk weighted assets, Minimum Capital Required To Be Considered Well Capitalized, Ratio 0.0650 0.0650
Tier 1 capital to risk weighted assets, Actual, Amount $ 194,064 $ 182,116
Tier 1 capital to risk weighted assets, Actual, Ratio 0.1149 0.1120
Tier 1 capital to risk weighted assets, Minimum Capital Required Plus Capital Conservation Buffer, Amount $ 143,525 $ 138,165
Tier 1 capital to risk weighted assets, Minimum Capital Required Plus Capital Conservation Buffer, Ratio 0.0850 0.0850
Tier 1 capital to risk weighted assets, Minimum Capital Required To Be Considered Well Capitalized, Amount $ 135,082 $ 130,038
Tier 1 capital to risk weighted assets, Minimum Capital Required To Be Considered Well Capitalized, Ratio 0.0800 0.0800
Total capital to risk weighted assets, Actual, Amount $ 209,147 $ 196,336
Total capital to risk weighted assets, Actual, Ratio 0.1239 0.1208
Total capital to risk weighted assets, Minimum Capital Required Plus Capital Conservation Buffer, Amount $ 177,295 $ 170,675
Total capital to risk weighted assets, Minimum Capital Required Plus Capital Conservation Buffer, Ratio 0.1050 0.1050
Total capital to risk weighted assets, Minimum Capital Required To Be Considered Well Capitalized, Amount $ 168,853 $ 162,547
Total capital to risk weighted assets, Minimum Capital Required To Be Considered Well Capitalized, Ratio 0.1000 0.1000
Tier 1 capital to average assets, Actual, Amount $ 194,064 $ 182,116
Tier 1 capital to average assets, Actual, Ratio 0.0893 0.0845
Tier 1 capital to average assets, Minimum Capital Required Plus Capital Conservation Buffer, Amount $ 86,910 $ 86,170
Tier 1 capital to average assets, Minimum Capital Required Plus Capital Conservation Buffer, Ratio 0.0400 0.0400
Tier 1 capital to average assets, Minimum Capital Required To Be Considered Well Capitalized, Amount $ 108,638 $ 107,713
Tier 1 capital to average assets, Minimum Capital Required To Be Considered Well Capitalized, Ratio 0.0500 0.0500