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Employee Benefit Plans (Details) - USD ($) $ in Millions | 12 Months Ended | 24 Months Ended
--- | --- | ---
Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2017 | Dec. 31, 2019
Employee Benefit Plans |  |  |  |  |
Expense relating to the 401(k) plan | $ 1.4 | $ 1.2 | $ 1.1 |  |
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%
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%
Participants vesting as percentage of discretionary matching contributions |  |  |  | 100.00% |

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- 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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X
- 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 -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 70 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942 + 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 No definition available. + Details
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X
- 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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X
- 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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Namespace Prefix: | us-gaap_
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- Details
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