Document and Entity Information [Abstract] Document Information [Table] Legal Entity [Axis] Entity [Domain] Represents the retirement plan 003. E B P 003 [Member] 401(k) Savings Plan and Trust Document Information [Line Items] Document Type Entity Registrant Name Entity Central Index Key Amendment Flag Statements of Net Assets Available for Benefits EBP, Statement of Net Asset Available for Benefit [Table] EBP, Statement of Net Asset Available for Benefit [Line Items] Statements of Net Assets Available for Benefits EBP, Asset [Abstract] Assets EBP, Noninterest-Bearing Cash Cash - noninterest bearing EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value Participant directed investments, at fair value Current Value EBP, Receivable [Abstract] Receivables: EBP, Employer Contribution, Receivable Employer match contribution receivable EBP, Note Receivable from Participant Notes receivable from participants EBP, Receivable Total receivables EBP, Net Asset Available for Benefit End of year Beginning of year Net assets available for benefits Statement of Changes in Net Assets Available for Benefits EBP, Statement of Change in Net Asset Available for Benefit [Table] EBP, Statement of Change in Net Asset Available for Benefit [Line Items] Statements of Net Assets Available for Benefits EBP, Change in Net Asset Available for Benefit, Increase [Abstract] Additions EBP, Change in Net Asset Available for Benefit, Increase (Decrease) from Income (Loss) on Investment [Abstract] Investment Income EBP, Change in Net Asset Available for Benefit, Increase (Decrease) from Gain (Loss) on Investment Net realized and unrealized gain in fair value of investments EBP, Change in Net Asset Available for Benefit, Increase from Interest and Dividend Income on Investment Dividend and interest income EBP, Change in Net Asset Available for Benefit, Increase (Decrease) from Income (Loss) on Investment Net investment gain EBP, Change in Net Asset Available for Benefit, Increase from Contribution [Abstract] Contributions EBP, Change in Net Asset Available for Benefit, Increase from Participant Contribution, Excluding Rollover Participants EBP, Change in Net Asset Available for Benefit, Increase from Employer Contribution, Cash and Noncash Employer EBP, Change in Net Asset Available for Benefit, Increase from Participant Contribution, Rollover Rollover EBP, Change in Net Asset Available for Benefit, Increase from Contribution Total contributions EBP, Change in Net Asset Available for Benefit, Increase from Interest Income on Note Receivable from Participant Interest income from notes receivable from participants EBP, Change in Net Asset Available for Benefit, Increase Total additions EBP, Change in Net Asset Available for Benefit, Decrease [Abstract] Deductions EBP, Change in Net Asset Available for Benefit, Decrease from Payment to Participant Benefit payments to participants or beneficiaries EBP, Change in Net Asset Available for Benefit, Decrease from Administrative Expense Administrative expenses Accounting and administrative services EBP, Change in Net Asset Available for Benefit, Decrease Total deductions EBP, Change in Net Asset Available for Benefit, Increase (Decrease) Net increase EBP, Change in Net Asset Available for Benefit, Increase (Decrease) [Abstract] Net assets available for benefits: Description of the Plan EBP, Description of Plan [Table] EBP, Description of Plan [Line Items] Description of the Plan EBP, Description of Plan [Text Block] Description of the Plan Summary of Significant Accounting Policies EBP, Accounting Policy [Table] EBP, Accounting Policy [Line Items] Summary of Significant Accounting Policies EBP, Summary of Accounting Policy [Text Block] Summary of Significant Accounting Policies Risk and Uncertainties EBP, Risk and Uncertainty [Table] EBP, Risk and Uncertainty [Line Items] Risk and Uncertainties EBP, Risk and Uncertainty [Text Block] Risk and Uncertainties Fair Value Measurements EBP, Investment, Fair Value and NAV [Table] EBP, Investment, Fair Value and NAV [Line Items] Fair Value Measurements EBP, Investment, Fair Value and NAV [Text Block] Fair Value Measurements Income Tax Status EBP, Tax Status [Table] EBP, Tax Status [Line Items] Income Tax Status EBP, Tax Status [Text Block] Income Tax Status Related Party Transactions EBP, Related Party and Party-in-Interest Transactions [Table] EBP, Related Party and Party-in-Interest Transactions [Line Items] Related Party Transactions EBP, Related Party and Party-in-Interest Transactions [Text Block] Related Party Transactions Schedule of Assets EBP, Schedule of Asset Held for Investment [Table] EBP, Schedule of Asset Held for Investment [Line Items] Schedule of Assets EBP, Schedule of Asset Held for Investment [Text Block] Schedule of Assets EBP, Basis of Accounting [Policy Text Block] Basis of Accounting EBP, Use of Estimate [Policy Text Block] Use of Estimates Disclosure of accounting policy for income recognition and investment valuation held by employee stock purchase, saving, or similar plan (employee benefit plan (EBP)). Employee Benefit Plan, Investment Valuation and Income Recognition [Policy Text Block] Investment Valuation and Income Recognition EBP, Note Receivable from Participant [Policy Text Block] Notes Receivable from Participants EBP, Payment to Participant [Policy Text Block] Payment of Benefits EBP, Expense [Policy Text Block] Administrative Expenses Disclosure of accounting policy for new accounting pronouncements in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)). Employee Benefit Plan, New Accounting Pronouncements [Policy Text Block] New Accounting Pronouncements Tabular disclosure of profit sharing contributions. Schedule of Profit Sharing Contributions [Table Text Block] Schedule of profit sharing contributions under 6 years EBP, Investment, Fair Value and NAV [Table Text Block] Schedule of investments measured at fair value Statistical Measurement [Axis] Statistical Measurement [Domain] Minimum [Member] Minimum Maximum [Member] Maximum EBP, Employer Contribution, Matching Percentage Percentage of employer contribution EBP, Employer Contribution, Participant Compensation Matched, Percentage Percentage of participant eligible compensation Percentage of employer matching contribution on additional participant contribution to employee stock purchase, saving, or similar plan (employee benefit plan (EBP)). Employee Benefit Plan, Employer Contribution, Matching Percentage On Additional Contribution Percentage of matching contribution on additional contribution Percentage of additional participant compensation eligible for employer matching contribution for participant in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)). Employee Benefit Plan , Employer Contribution, Additional Participant Compensation Matched, Percentage Percentage of matching contribution for employee earnings on additional contribution Percentage of participant compensation, equal to or greater than 5 percent, that is elected by the participant and is eligible for employer matching contribution for participant in employee stock purchase, savings, or similar plan (employee benefit plan (EBP)). Employee Benefit Plan , Employer Contribution, Participant Compensation 5% or More Elected, Matched Percentage Total company matched percentage Percentage of participant compensation representing the minimum amount elected by the participant that is eligible for employer matching contribution for participant in employee stock purchase, savings, or similar plan (employee benefit plan (EBP)). Employee Benefit Plan , Employer Contribution, Minimum Participant Compensation Elected, Percentage Contribution rate Period of service required for a participant to become eligible for employer matching contributions in an employee stock purchase, savings, or similar plan (employee benefit plan (EBP)). Employee Benefit Plan , Matching Contribution Eligibility, Period of Service Number of years of service, Eligibility of matching contributions Represents the percentage of vesting. Employee Benefit Plan, Vesting Percentage Vesting percentage Number of years of service required for a participant to become eligible for profit-sharing contributions in an employee stock purchase, savings, or similar plan (employee benefit plan (EBP)). Employee Benefit Plan , Profit Sharing Contributions Eligibility, Number of Years of Service Number of years of service, Eligibility of profit-sharing contributions Amount of employer profit-sharing contributions allocated to participants in an employee stock purchase, savings, or similar plan (employee benefit plan (EBP)). Employee Benefit Plan , Profit Sharing Contributions, Amount Profit-sharing contributions EBP, Forfeited Nonvested Account, Decrease from Employer Contribution Forfeitures used to reduce the employer matching contributions Age at which a participant becomes eligible to receive in-service distributions from an employee stock purchase, savings, or similar plan (employee benefit plan (EBP)). Employee Benefit Plan , Participant Age Eligibility to Receive In-service Distributions In-service distribution, Participant's age eligibility EBP, Note Receivable from Participant, Account, Maximum Borrowing, Amount Note receivable, maximum borrowing amount EBP, Note Receivable from Participant, Account, Maximum Borrowing, to Total Account, Percentage Note receivable, maximum borrowing percentage Term of participant loan of employee stock purchase, saving, or similar plan (employee benefit plan (EBP)). Employee Benefit Plan, Note Receivable From Participant, Term Loan term Scenario [Axis] Scenario [Domain] Represents information pertaining to scenario in which number of years of vesting service completed, upto year 1. Number of Years of Vesting Service Completed, Upto Year 1 [Member] Year 0 - 1 Represents information pertaining to scenario in which number of years of vesting service completed, upto year 2. Number of Years of Vesting Service Completed, Upto Year 2 [Member] Year 2 Represents information pertaining to scenario in which number of years of vesting service completed, upto year 3. Number of Years of Vesting Service Completed, Upto Year 3 [Member] Year 3 Represents information pertaining to scenario in which number of years of vesting service completed, upto year 4. Number of Years of Vesting Service Completed, Upto Year 4 [Member] Year 4 Represents information pertaining to scenario in which number of years of vesting service completed, upto year 5. Number of Years of Vesting Service Completed, Upto Year 5 [Member] Year 5 Represents information pertaining to scenario in which number of years of vesting service completed, upto year 6. Number of Years of Vesting Service Completed, Upto Year 6 [Member] Year 6 Investment Type [Axis] Investments [Domain] Mutual Fund [Member] Registered investment companies EBP, Employer, Common Stock [Member] Company stock Money Market Funds [Member] Money market account Common Collective Trust [Member] Common/collective trusts Represents the information pertains to diversified equity portfolio in common collective trust. Defined Benefit Plan, Common Collective Trust, Diversified Equity Portfolio [Member] Diversified Equity Portfolio Represents the information pertains to strategic dividend fund in common collective trust. Defined Benefit Plan, Common Collective Trust, Strategic Dividend Fund [Member] Strategic Dividend Fund Represents the information pertains to bond fund in common collective trust. Defined Benefit Plan, Common Collective Trust, Bond Fund [Member] Bond Fund Represents the information pertains to balanced fund in common collective trust. Defined Benefit Plan, Common Collective Trust, Balanced Fund [Member] Balanced Fund Represents the information pertains to stable value fund in common collective trust. Defined Benefit Plan, Common Collective Trust, Stable Value Fund [Member] Stable Value Fund Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Domain] Fair Value, Inputs, Level 1, Level 2, and Level 3 [Member] Fair value Fair Value, Inputs, Level 1 [Member] Level 1 Fair Value, Inputs, Level 2 [Member] Level 2 Fair Value Measured at Net Asset Value Per Share [Member] NAV EBP, Net Asset Value per Share or Unit Established unit value EBP, Fair Value, Investment, NAV, Redemption, Notice Period Notice period EBP, Fair Value, Investment, NAV, Unfunded Commitment Unfunded commitments EBP, Tax Determination Letter, Obtained [true false] Determination letter obtained EBP, Tax Determination Letter, Date Determination letter date EBP, Related Party and Party-in-Interest [Axis] EBP, Related Party and Party-in-Interest [Domain] Employer of participant in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)). Employee Benefit Plan Employer [Member] Company EBP, Trustee [Member] Old Second National Bank EBP, Investment, Purchased, Number of Shares Shares purchased EBP, Investment Acquired, Excluding Plan Interest in Master Trust, Cost Shares purchased at cost EBP, Investment, Sold, Number of Shares Shares sold EBP, Investment Sold, Excluding Plan Interest in Master Trust, Selling Price Proceeds from shares sold EBP, Investment, Number of Shares Number of Units/Shares EBP, Change in Net Asset Available for Benefit, Increase from Dividend Income on Investment Dividends received Amount of administrative expenses incurred by trustee in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)). Employee Benefit Plan Administration Cost Incurred By Trustee Accounting and administrative services paid by trustee Investment, Identifier [Axis] Entity Tax Identification Number Entity tax identification number EBP, Plan Number Plan number EBP, Investment, Issuer Name [Extensible Enumeration] EBP, Investment, Current Value, Type [Extensible Enumeration] EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Current Value Current Value EBP, Asset Held for Investment, Participant Loan, after Deemed Distribution Notes receivable from participants EBP, Asset Held for Investment, Participant Loan, Interest Rate Interest rates of notes receivable from participants EBP, Asset Held for Investment Total Investments and Loans EBP, Asset Held for Investment, Party-in-Interest [true false] EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration]