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Regulatory Capital - Regulatory Capital Ratios (Details) $ in Thousands | Sep. 30, 2025 USD ($) | Dec. 31, 2024 USD ($)
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Compliance with Regulatory Capital Requirements under Banking Regulations |  |
Total capital | $ 452,731 | $ 421,639
Total capital to risk-weighted assets | 0.1218 | 0.1208
Total capital, Minimum Required for Capital Adequacy Purposes | $ 297,419 | $ 279,330
Total capital to risk-weighted assets, Minimum Required for Capital Adequacy Purposes | 0.08 | 0.08
Capital Required for Capital Adequacy Plus Capital Conservation Buffer | $ 390,363 | $ 366,621
Capital Required for Capital Adequacy Plus Conservation Buffer to Risk Weighted Assets | 10.50% | 10.50%
Tier 1 capital | $ 359,409 | $ 329,796
Tier 1 capital to risk-weighted assets | 0.0967 | 0.0945
Tier 1 capital, Minimum Required for Capital Adequacy Purposes | $ 223,064 | $ 209,498
Tier 1 capital to risk-weighted assets, Minimum Required for Capital Adequacy Purposes | 0.06 | 0.06
Tier One Risk Based Capital Required for Capital Adequacy Plus Capital Conservation Buffer | $ 316,008 | $ 296,788
Tier One Risk Based Capital Required for Capital Adequacy Plus Conservation Buffer to Risk Weighted Assets | 8.50% | 8.50%
Common equity tier 1 capital | $ 347,417 | $ 317,804
Common equity tier 1 capital to risk-weighted assets | 9.34% | 9.10%
Common equity tier 1 capital, Minimum Required for Capital Adequacy Purposes | $ 167,298 | $ 157,123
Common equity tier 1 capital to risk-weighted assets, Minimum Required for Capital Adequacy Purposes | 4.50% | 4.50%
Common Equity Tier One Capital Required for Capital Adequacy Plus Capital Conservation Buffer | $ 260,242 | $ 244,414
Common Equity Tier One Capital Required for Capital Adequacy Plus Conservation Buffer to Risk Weighted Assets | 7.00% | 7.00%
Tier 1 leverage capital | $ 359,409 | $ 329,796
Tier 1 leverage capital to average assets | 0.0887 | 0.0878
Tier 1 leverage capital, Minimum Required for Capital Adequacy Purposes | $ 162,031 | $ 150,256
Tier 1 leverage capital to average assets, Minimum Required for Capital Adequacy Purposes | 0.04 | 0.04
Tier One Leverage Capital Required for Capital Adequacy Plus Capital Conservation Buffer | $ 162,031 | $ 150,256
Tier One Leverage Capital Required for Capital Adequacy Plus Conservation Buffer to Risk Weighted Assets | 4.00% | 4.00%
First Business Bank |  |
Compliance with Regulatory Capital Requirements under Banking Regulations |  |
Total capital | $ 450,613 | $ 417,965
Total capital to risk-weighted assets | 0.1212 | 0.1197
Total capital, Minimum Required for Capital Adequacy Purposes | $ 297,482 | $ 279,342
Total capital to risk-weighted assets, Minimum Required for Capital Adequacy Purposes | 0.08 | 0.08
Capital Required for Capital Adequacy Plus Capital Conservation Buffer | $ 390,445 | $ 366,636
Capital Required for Capital Adequacy Plus Conservation Buffer to Risk Weighted Assets | 10.50% | 10.50%
Total capital, Minimum Required to be Well Capitalized Under Prompt Corrective Action Requirements | $ 371,853 | $ 349,177
Total capital to risk-weighted assets, Minimum Required to be Well Capitalized Under Prompt Corrective Action Requirements | 0.10 | 0.10
Tier 1 capital | $ 412,067 | $ 380,811
Tier 1 capital to risk-weighted assets | 0.1108 | 0.1091
Tier 1 capital, Minimum Required for Capital Adequacy Purposes | $ 223,112 | $ 209,506
Tier 1 capital to risk-weighted assets, Minimum Required for Capital Adequacy Purposes | 0.06 | 0.06
Tier One Risk Based Capital Required for Capital Adequacy Plus Capital Conservation Buffer | $ 316,075 | $ 296,801
Tier One Risk Based Capital Required for Capital Adequacy Plus Conservation Buffer to Risk Weighted Assets | 8.50% | 8.50%
Tier 1 capital, Minimum Required to be Well Capitalized Under Prompt Corrective Action Requirements | $ 297,482 | $ 279,342
Tier 1 capital to risk weighted assets, Minimum Required to be Well Capitalized Under Prompt Corrective Action Requirements | 0.08 | 0.08
Common equity tier 1 capital | $ 412,067 | $ 380,811
Common equity tier 1 capital to risk-weighted assets | 11.08% | 10.91%
Common equity tier 1 capital, Minimum Required for Capital Adequacy Purposes | $ 167,334 | $ 157,130
Common equity tier 1 capital to risk-weighted assets, Minimum Required for Capital Adequacy Purposes | 4.50% | 4.50%
Common Equity Tier One Capital Required for Capital Adequacy Plus Capital Conservation Buffer | $ 260,297 | $ 244,424
Common Equity Tier One Capital Required for Capital Adequacy Plus Conservation Buffer to Risk Weighted Assets | 7.00% | 7.00%
Common equity tier 1 capital, Minimum Required to Be Well Capitalized Under Prompt Corrective Action Requirements | $ 241,704 | $ 226,965
Common equity tier 1 capital to risk-weighted assets, Minimum Required to Be Well Capitalized Under Prompt Corrective Action Requirements | 6.50% | 6.50%
Tier 1 leverage capital | $ 412,067 | $ 380,811
Tier 1 leverage capital to average assets | 0.1018 | 0.1017
Tier 1 leverage capital, Minimum Required for Capital Adequacy Purposes | $ 161,895 | $ 150,207
Tier 1 leverage capital to average assets, Minimum Required for Capital Adequacy Purposes | 0.04 | 0.04
Tier One Leverage Capital Required for Capital Adequacy Plus Capital Conservation Buffer | $ 161,895 | $ 150,207
Tier One Leverage Capital Required for Capital Adequacy Plus Conservation Buffer to Risk Weighted Assets | 4.00% | 4.00%
Tier 1 leverage capital, Minimum Required to be Well Capitalized Under Prompt Corrective Action Requirements | $ 202,369 | $ 187,759
Tier 1 leverage capital to average assets, Minimum Required to be Well Capitalized Under Prompt Corrective Action Requirements | 0.05 | 0.05

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