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Employee Benefit Plans (Details) - USD ($) $ in Millions | 12 Months Ended | 36 Months Ended
--- | --- | ---
Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2023
Employee Benefit Plans |  |  |  |
Expense relating to the 401(k) plan | $ 2.2 | $ 2.0 | $ 1.4 |
Old Second Bancorp Inc Employees 401(k) Savings Plan and Trust |  |  |  |
Employee Benefit Plans |  |  |  |
Company's discretionary matching contributions to the Plan (as a percent) | 100.00% | 100.00% | 100.00% |
Company's discretionary matching contributions to the Plan (as a percent) |  |  |  | 50.00%
Percentage of compensation contributed to the Plan matched by employer (as a percent) |  |  |  | 2.00%
Percentage of compensation contributed to the Plan matched by employer | 3.00% | 3.00% | 3.00% |
Participants vesting as percentage of discretionary matching contributions | 100.00% |  |  |

X
- Definition Second percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan. + References No definition available. + Details
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- Definition Second percentage employer matches of the employee's percentage contribution matched. + References No definition available. + Details
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- Definition Amount of cost for defined contribution plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 70 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480794/715-70-50-1 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 70 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480794/715-70-50-1 + Details
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- Definition Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan. + References No definition available. + Details
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- Definition Percentage employer matches of the employee's percentage contribution matched. + References No definition available. + Details
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- Definition Percentage of employer's matching contributions to a defined contribution plan that vests in a given year. + References No definition available. + Details
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- Details
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