Schedule of Assets (Details) - 401(k) Savings Plan and Trust
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12 Months Ended |
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Dec. 31, 2025
USD ($)
shares
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|---|
| Schedule of Assets |
|
| Entity tax identification number |
36-3143493
|
| Plan number |
003
|
| Notes receivable from participants |
$ 2,149,602
|
| Total Investments and Loans |
$ 119,733,441
|
| Investment, Identifier [Axis]: American Century Mid Cap Value CL R6, Registered Investment Companies |
|
| Schedule of Assets |
|
| EBP, Investment, Issuer Name [Extensible Enumeration] |
osbc:AmericanCenturyMidCapValueClR6Member
|
| EBP, Investment, Current Value, Type [Extensible Enumeration] |
Mutual Fund [Member]
|
| Number of Units/Shares | shares |
16,545
|
| Current Value |
$ 244,865
|
| EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration] |
us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
|
| Investment, Identifier [Axis]: American Funds New World R6, Registered Investment Companies |
|
| Schedule of Assets |
|
| EBP, Investment, Issuer Name [Extensible Enumeration] |
osbc:AmericanFundsNewWorldR6Member
|
| EBP, Investment, Current Value, Type [Extensible Enumeration] |
Mutual Fund [Member]
|
| Number of Units/Shares | shares |
14,501
|
| Current Value |
$ 1,351,084
|
| EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration] |
us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
|
| Investment, Identifier [Axis]: Dodge & Cox Stock Fund, Registered Investment Companies |
|
| Schedule of Assets |
|
| EBP, Investment, Issuer Name [Extensible Enumeration] |
osbc:DodgeCoxStockFundMember
|
| EBP, Investment, Current Value, Type [Extensible Enumeration] |
Mutual Fund [Member]
|
| Number of Units/Shares | shares |
402,971
|
| Current Value |
$ 6,685,290
|
| EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration] |
us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
|
| Investment, Identifier [Axis]: Federated Capital Preservation Trust Fund, Common/Collective Trust Fund, Stable Value |
|
| Schedule of Assets |
|
| EBP, Investment, Issuer Name [Extensible Enumeration] |
osbc:FederatedCapitalPreservationTrustFundMember
|
| EBP, Investment, Current Value, Type [Extensible Enumeration] |
Common Collective Trust [Member]
|
| Number of Units/Shares | shares |
567,316
|
| Current Value |
$ 5,673,161
|
| EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration] |
us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
|
| Investment, Identifier [Axis]: Federated Ultra Short DB FD Inst SH, Registered Investment Companies |
|
| Schedule of Assets |
|
| EBP, Investment, Issuer Name [Extensible Enumeration] |
osbc:DodgeCoxStockFundMember
|
| EBP, Investment, Current Value, Type [Extensible Enumeration] |
Mutual Fund [Member]
|
| Number of Units/Shares | shares |
83,411
|
| Current Value |
$ 777,387
|
| EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration] |
us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
|
| Investment, Identifier [Axis]: Fidelity Mid Cap Index, Registered Investment Companies |
|
| Schedule of Assets |
|
| EBP, Investment, Issuer Name [Extensible Enumeration] |
osbc:FederatedUltraShortDbFdInstShMember
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| EBP, Investment, Current Value, Type [Extensible Enumeration] |
Mutual Fund [Member]
|
| Number of Units/Shares | shares |
63,919
|
| Current Value |
$ 2,360,517
|
| EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration] |
us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
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| Investment, Identifier [Axis]: JPMorgan Small Cap Growth Fund R6, Registered Investment Companies |
|
| Schedule of Assets |
|
| EBP, Investment, Issuer Name [Extensible Enumeration] |
osbc:JpmorganSmallCapGrowthFundR6Member
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| EBP, Investment, Current Value, Type [Extensible Enumeration] |
Mutual Fund [Member]
|
| Number of Units/Shares | shares |
30,329
|
| Current Value |
$ 681,785
|
| EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration] |
us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
|
| Investment, Identifier [Axis]: MFS Intl Growth CL R6, Registered Investment Companies |
|
| Schedule of Assets |
|
| EBP, Investment, Issuer Name [Extensible Enumeration] |
osbc:MfsIntlGrowthClR6Member
|
| EBP, Investment, Current Value, Type [Extensible Enumeration] |
Mutual Fund [Member]
|
| Number of Units/Shares | shares |
4,605
|
| Current Value |
$ 218,633
|
| EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration] |
us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
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| Investment, Identifier [Axis]: Metropolitan West Total Return BD PL, Registered Investment Companies |
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| Schedule of Assets |
|
| EBP, Investment, Issuer Name [Extensible Enumeration] |
osbc:MetropolitanWestTotalReturnBdPlMember
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| EBP, Investment, Current Value, Type [Extensible Enumeration] |
Mutual Fund [Member]
|
| Number of Units/Shares | shares |
368,819
|
| Current Value |
$ 3,171,842
|
| EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration] |
us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
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| Investment, Identifier [Axis]: Neuberger Berman Mid Cap Growth Inst, Registered Investment Companies |
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| Schedule of Assets |
|
| EBP, Investment, Issuer Name [Extensible Enumeration] |
osbc:NeubergerBermanMidCapGrowthInstMember
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| EBP, Investment, Current Value, Type [Extensible Enumeration] |
Mutual Fund [Member]
|
| Number of Units/Shares | shares |
245,867
|
| Current Value |
$ 3,604,410
|
| EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration] |
us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
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| Investment, Identifier [Axis]: Old Second Bancorp, Inc. common stock, Company Stock |
|
| Schedule of Assets |
|
| EBP, Investment, Issuer Name [Extensible Enumeration] |
osbc:OldSecondBancorpInc.Member
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| EBP, Investment, Current Value, Type [Extensible Enumeration] |
EBP, Employer, Common Stock [Member]
|
| Number of Units/Shares | shares |
645,509
|
| Current Value |
$ 12,587,426
|
| EBP, Asset Held for Investment, Party-in-Interest [true false] |
true
|
| EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration] |
us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
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| Investment, Identifier [Axis]: Schwab Retirement Value Advantage Money Fund, Money Market Account |
|
| Schedule of Assets |
|
| EBP, Investment, Issuer Name [Extensible Enumeration] |
osbc:SchwabRetirementValueAdvantageMoneyFundMember
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| EBP, Investment, Current Value, Type [Extensible Enumeration] |
Money Market Funds [Member]
|
| Number of Units/Shares | shares |
402
|
| Current Value |
$ 402
|
| EBP, Asset Held for Investment, Party-in-Interest [true false] |
true
|
| EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration] |
us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
|
| Investment, Identifier [Axis]: Schwab Small Cap Index, Registered Investment Companies |
|
| Schedule of Assets |
|
| EBP, Investment, Issuer Name [Extensible Enumeration] |
osbc:SchwabSmallCapIndexMember
|
| EBP, Investment, Current Value, Type [Extensible Enumeration] |
Mutual Fund [Member]
|
| Number of Units/Shares | shares |
72,247
|
| Current Value |
$ 2,876,872
|
| EBP, Asset Held for Investment, Party-in-Interest [true false] |
true
|
| EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration] |
us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
|
| Investment, Identifier [Axis]: T. Rowe Price All-Cap Opportunities, Registered Investment Companies |
|
| Schedule of Assets |
|
| EBP, Investment, Issuer Name [Extensible Enumeration] |
osbc:T.RowePriceAllCapOpportunitiesMember
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| EBP, Investment, Current Value, Type [Extensible Enumeration] |
Mutual Fund [Member]
|
| Number of Units/Shares | shares |
116,021
|
| Current Value |
$ 9,161,002
|
| EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration] |
us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
|
| Investment, Identifier [Axis]: T. Rowe Price Intl Value Eqty FD 1, Registered Investment Companies |
|
| Schedule of Assets |
|
| EBP, Investment, Issuer Name [Extensible Enumeration] |
osbc:T.RowePriceIntlValueEqtyFd1Member
|
| EBP, Investment, Current Value, Type [Extensible Enumeration] |
Mutual Fund [Member]
|
| Number of Units/Shares | shares |
13,552
|
| Current Value |
$ 318,876
|
| EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration] |
us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
|
| Investment, Identifier [Axis]: T. Rowe Price Retirement 2020 I, Registered Investment Companies |
|
| Schedule of Assets |
|
| EBP, Investment, Issuer Name [Extensible Enumeration] |
osbc:T.RowePriceRetirement2020IMember
|
| EBP, Investment, Current Value, Type [Extensible Enumeration] |
Mutual Fund [Member]
|
| Number of Units/Shares | shares |
24,268
|
| Current Value |
$ 478,072
|
| EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration] |
us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
|
| Investment, Identifier [Axis]: T. Rowe Price Retirement 2030 I, Registered Investment Companies |
|
| Schedule of Assets |
|
| EBP, Investment, Issuer Name [Extensible Enumeration] |
osbc:T.RowePriceRetirement2030IMember
|
| EBP, Investment, Current Value, Type [Extensible Enumeration] |
Mutual Fund [Member]
|
| Number of Units/Shares | shares |
116,344
|
| Current Value |
$ 3,223,884
|
| EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration] |
us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
|
| Investment, Identifier [Axis]: T. Rowe Price Retirement 2040 I, Registered Investment Companies |
|
| Schedule of Assets |
|
| EBP, Investment, Issuer Name [Extensible Enumeration] |
osbc:T.RowePriceRetirement2040IMember
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| EBP, Investment, Current Value, Type [Extensible Enumeration] |
Mutual Fund [Member]
|
| Number of Units/Shares | shares |
116,289
|
| Current Value |
$ 3,998,018
|
| EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration] |
us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
|
| Investment, Identifier [Axis]: T. Rowe Price Retirement 2050 I, Registered Investment Companies |
|
| Schedule of Assets |
|
| EBP, Investment, Issuer Name [Extensible Enumeration] |
osbc:T.RowePriceRetirement2050IMember
|
| EBP, Investment, Current Value, Type [Extensible Enumeration] |
Mutual Fund [Member]
|
| Number of Units/Shares | shares |
142,935
|
| Current Value |
$ 3,091,677
|
| EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration] |
us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
|
| Investment, Identifier [Axis]: T. Rowe Price Retirement 2060 I, Registered Investment Companies |
|
| Schedule of Assets |
|
| EBP, Investment, Issuer Name [Extensible Enumeration] |
osbc:T.RowePriceRetirement2060IMember
|
| EBP, Investment, Current Value, Type [Extensible Enumeration] |
Mutual Fund [Member]
|
| Number of Units/Shares | shares |
81,078
|
| Current Value |
$ 1,540,488
|
| EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration] |
us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
|
| Investment, Identifier [Axis]: The Old Second National Bank of Aurora Common Trust Fund for Corporate Retirement Plans, Balanced Fund, Common/Collective Trust Funds |
|
| Schedule of Assets |
|
| EBP, Investment, Issuer Name [Extensible Enumeration] |
osbc:OldSecondNationalBankOfAuroraCommonTrustFundForCorporateRetirementPlansMember
|
| EBP, Investment, Current Value, Type [Extensible Enumeration] |
Common Collective Trust [Member]
|
| Number of Units/Shares | shares |
267,292
|
| Current Value |
$ 10,702,191
|
| EBP, Asset Held for Investment, Party-in-Interest [true false] |
true
|
| EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration] |
us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
|
| Investment, Identifier [Axis]: The Old Second National Bank of Aurora Common Trust Fund for Corporate Retirement Plans, Bond Fund, Common/Collective Trust Funds |
|
| Schedule of Assets |
|
| EBP, Investment, Issuer Name [Extensible Enumeration] |
osbc:OldSecondNationalBankOfAuroraCommonTrustFundForCorporateRetirementPlansMember
|
| EBP, Investment, Current Value, Type [Extensible Enumeration] |
Common Collective Trust [Member]
|
| Number of Units/Shares | shares |
28,214
|
| Current Value |
$ 6,225,407
|
| EBP, Asset Held for Investment, Party-in-Interest [true false] |
true
|
| EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration] |
us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
|
| Investment, Identifier [Axis]: The Old Second National Bank of Aurora Common Trust Fund for Corporate Retirement Plans, Diversified Equity Portfolio, Common/Collective Trust Funds |
|
| Schedule of Assets |
|
| EBP, Investment, Issuer Name [Extensible Enumeration] |
osbc:OldSecondNationalBankOfAuroraCommonTrustFundForCorporateRetirementPlansMember
|
| EBP, Investment, Current Value, Type [Extensible Enumeration] |
Common Collective Trust [Member]
|
| Number of Units/Shares | shares |
61,982
|
| Current Value |
$ 12,269,037
|
| EBP, Asset Held for Investment, Party-in-Interest [true false] |
true
|
| EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration] |
us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
|
| Investment, Identifier [Axis]: The Old Second National Bank of Aurora Common Trust Fund for Corporate Retirement Plans, Strategic Dividend Fund, Common/Collective Trust Funds |
|
| Schedule of Assets |
|
| EBP, Investment, Issuer Name [Extensible Enumeration] |
osbc:OldSecondNationalBankOfAuroraCommonTrustFundForCorporateRetirementPlansMember
|
| EBP, Investment, Current Value, Type [Extensible Enumeration] |
Common Collective Trust [Member]
|
| Number of Units/Shares | shares |
157,261
|
| Current Value |
$ 5,531,072
|
| EBP, Asset Held for Investment, Party-in-Interest [true false] |
true
|
| EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration] |
us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
|
| Investment, Identifier [Axis]: Vanguard 500 Index Fund, Registered Investment Companies |
|
| Schedule of Assets |
|
| EBP, Investment, Issuer Name [Extensible Enumeration] |
osbc:Vanguard500IndexFundMember
|
| EBP, Investment, Current Value, Type [Extensible Enumeration] |
Mutual Fund [Member]
|
| Number of Units/Shares | shares |
22,486
|
| Current Value |
$ 14,207,770
|
| EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration] |
us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
|
| Investment, Identifier [Axis]: Vanguard Developed Markets Index, Registered Investment Companies |
|
| Schedule of Assets |
|
| EBP, Investment, Issuer Name [Extensible Enumeration] |
osbc:VanguardDevelopedMarketsIndexMember
|
| EBP, Investment, Current Value, Type [Extensible Enumeration] |
Mutual Fund [Member]
|
| Number of Units/Shares | shares |
299,962
|
| Current Value |
$ 6,020,229
|
| EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration] |
us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
|
| Investment, Identifier [Axis]: Vanguard Small Cap Value Index Admi, Registered Investment Companies |
|
| Schedule of Assets |
|
| EBP, Investment, Issuer Name [Extensible Enumeration] |
osbc:VanguardSmallCapValueIndexAdmiMember
|
| EBP, Investment, Current Value, Type [Extensible Enumeration] |
Mutual Fund [Member]
|
| Number of Units/Shares | shares |
6,399
|
| Current Value |
$ 582,442
|
| EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration] |
us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
|
| Minimum |
|
| Schedule of Assets |
|
| Interest rates of notes receivable from participants |
3.25%
|
| Maximum |
|
| Schedule of Assets |
|
| Interest rates of notes receivable from participants |
10.50%
|