XML 117 R100.htm IDEA: XBRL DOCUMENT
v3.20.4

Employee Benefit Plans (Details) - USD ($) $ in Millions | 12 Months Ended | 24 Months Ended
--- | --- | ---
Dec. 31, 2020 | Dec. 31, 2017 | Dec. 31, 2019
Employee Benefit Plans |  |  |
Expense relating to the 401(k) plan | $ 1.2 |  |
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% |
Expense relating to the 401(k) plan |  |  | $ 1.1

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
Name: | osbc_DefinedContributionPlanEmployerMatchingContributionPercentOfEmployeesGrossPayTwo
Namespace Prefix: | osbc_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Second percentage employer matches of the employee's percentage contribution matched. + References No definition available. + Details
Name: | osbc_DefinedContributionPlanEmployerMatchingContributionPercentOfMatchTwo
Namespace Prefix: | osbc_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- 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
Name: | us-gaap_DefinedContributionPlanCostRecognized
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- 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
Name: | us-gaap_DefinedContributionPlanDisclosureLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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
Name: | us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage employer matches of the employee's percentage contribution matched. + References No definition available. + Details
Name: | us-gaap_DefinedContributionPlanEmployerMatchingContributionPercentOfMatch
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage of employer's matching contributions to a defined contribution plan that vests in a given year. + References No definition available. + Details
Name: | us-gaap_DefinedContributionPlanEmployersMatchingContributionAnnualVestingPercentage
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_RetirementPlanNameAxis=osbc_OldSecondBancorpIncEmployees401KSavingsPlanAndTrustMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |