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Regulatory & Capital Matters (Details) | Dec. 31, 2017 | Dec. 31, 2016
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Regulatory & Capital Matters |  |
Tier 1 capital leverage ratio (as a percent) | 10.08% | 8.90%
Risk-based capital ratio (as a percent) | 12.93% | 12.29%
Old Second National Bank |  |
Regulatory & Capital Matters |  |
Tier 1 capital leverage ratio (as a percent) | 10.79% | 10.24%
Risk-based capital ratio (as a percent) | 13.78% | 13.45%
Minimum | Old Second National Bank |  |
Regulatory & Capital Matters |  |
Tier 1 capital leverage ratio (as a percent) | 8.00% |
Risk-based capital ratio (as a percent) | 12.00% |

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