Trading Arrangements, by Individual Trading Arrangements, by Individual [Table] Trading Arrangement: Trading Arrangement [Axis] Maximum Maximum [Member] Interest rate, stated (as a percent) Investment Interest Rate, Stated Investment Interest Rate, Stated Percentage of portfolio investments containing limited consultation with financial advisory services firm (as a percent) Investment Company, Portfolio Investments, Limited Consultation With Financial Advisory Services Firm, Percentage Investment Company, Portfolio Investments, Limited Consultation With Financial Advisory Services Firm, Percentage Title of 12(b) Security Subsequent Event Subsequent Event [Member] Debt instrument, weighted-average annual interest rate (as a percent) Debt, Weighted Average Interest Rate Adjustment to Compensation, Amount Adjustment to Compensation Amount Number of portfolio investments in entities Investment Company, Number Of Portfolio Investments, Entities Investment Company, Number Of Portfolio Investments, Entities Financial Instrument [Axis] Financial Instrument [Axis] Schedule of Portfolio Investments by Level in the Fair Value Hierarchy Fair Value, Assets Measured on Recurring Basis [Table Text Block] Freeport Financial Funds Freeport Financial Funds [Member] Freeport Financial Funds State and other Investment Income, Operating, Deferred State And Other Tax Expense (Benefit) Investment Income, Operating, Deferred State And Other Tax Expense (Benefit) Affiliate investments: Investment, Affiliated Issuer, Noncontrolled [Member] Issuance of restricted stock, net of forfeited shares (in shares) Stock Issued During Period, Shares, Restricted Stock Award, Net of Forfeitures Interest and dividend receivable and prepaids and other assets Increase (Decrease) In Interest And Dividend Receivable And Other Assets Increase (Decrease) In Interest And Dividend Receivable And Other Assets Measurement Frequency [Axis] Measurement Frequency [Axis] ZRG Partners, LLC ZRG Partners, LLC [Member] ZRG Partners, LLC Entity Common Stock, Shares Outstanding Financial Instrument Performance Status [Domain] Financial Instrument Performance Status [Domain] Federal Investment Income, Operating, Deferred Federal Tax Expense (Benefit) Investment Income, Operating, Deferred Federal Tax Expense (Benefit) Fee income Fee income Fee Income RELATED PARTY TRANSACTIONS Related Party Transactions Disclosure [Text Block] Machinery Machinery [Member] Machinery Accretive effect of DRIP issuance (issuing shares above NAV per share) (in dollars per share) Investment Company, Effect Of Dividend Reinvestment Plan, Per Share Investment Company, Effect Of Dividend Reinvestment Plan, Per Share Investment Company, Nonconsolidated Subsidiary [Axis] Investment Company, Nonconsolidated Subsidiary [Axis] Common stock, par value (in dollars per share) Common Stock, Par or Stated Value Per Share Career Team Holdings, LLC Career Team Holdings, LLC [Member] Career Team Holdings, LLC Intangible asset Intangible Asset, Excluding Goodwill, after Accumulated Amortization Nonvested beginning balance (in shares) Nonvested ending balance (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Number Income tax provision Investment Company, Tax Basis, Income Tax Provision Investment Company, Tax Basis, Income Tax Provision O 2025 A2 Regular Dividends O 2025 A2 Regular Dividends [Member] O 2025 A2 Regular Dividends Outstanding Aggregate Erroneous Compensation Amount Outstanding Aggregate Erroneous Compensation Amount OMi Topco, LLC OMi Topco, LLC [Member] OMi Topco, LLC Number of reportable segments Number of Reportable Segments First lien debt Debt Securities, First Lien [Member] Debt Securities, First Lien AVEX Aviation Holdings, LLC AVEX Aviation Holdings, LLC [Member] AVEX Aviation Holdings, LLC Specialty Retail Specialty Retail [Member] Specialty Retail JorVet Holdings, LLC JorVet Holdings, LLC [Member] JorVet Holdings, LLC Entity Address, City or Town Less net restricted stock granted (in shares) Granted (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period Rabbi Trust Rabbi Trust [Member] Rabbi Trust Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items] Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items] Annualized total return on investments (as a percent) Investment Company, Annualized Total Return Investment Company, Annualized Total Return Statement of Financial Position [Abstract] Title of Individual [Domain] Title and Position [Domain] Peer Group Total Shareholder Return Amount Peer Group Total Shareholder Return Amount Significant Other Observable Inputs (Level 2) Fair Value, Inputs, Level 2 [Member] Total Shareholder Return Vs Peer Group Total Shareholder Return Vs Peer Group [Text Block] Net investment income (in dollars per share) Investment Company, Investment Income (Loss), Per Share, Basic Non-Rule 10b5-1 Arrangement Terminated Non-Rule 10b5-1 Arrangement Terminated [Flag] Total Rate Interest rate (as a percent) Investment Interest Rate SPV Facility SPV Facility [Member] SPV Facility Floor rate (as a percent) Investment, Interest Rate, Floor Dividends [Domain] Dividends [Domain] CompareNetworks Topco, LLC CompareNetworks Topco, LLC [Member] CompareNetworks Topco, LLC Subsequent Event Type [Axis] Subsequent Event Type [Axis] Variable Rate Component One Variable Rate Component One [Member] Variable Rate Component One Unsecured Revolving Promissory Note Unsecured Revolving Promissory Note [Member] Unsecured Revolving Promissory Note Concentration Risk Type [Axis] Concentration Risk Type [Axis] Schedule of Long-Term Debt Instruments [Table] Schedule of Long-Term Debt Instruments [Table] Debt Instrument, interest rate, yield-to-worst Debt Instrument, Interest Rate, Yield-To-Worst Debt Instrument, Interest Rate, Yield-To-Worst Contractual obligation, number of additional investments, investment period expired with remaining commitments restricted for fund expenses Investment Company, Number Of Additional Investments, Investment Period Expired With Remaining Commitments Restricted For Fund Expenses Investment Company, Number Of Additional Investments, Investment Period Expired With Remaining Commitments Restricted For Fund Expenses Joerns Healthcare, LLC Joerns Healthcare, LLC [Member] Joerns Healthcare, LLC 2015 Deferred Compensation Plan The 2015 Deferred Compensation Plan [Member] The 2015 Deferred Compensation Plan Use of Estimates Use of Estimates, Policy [Policy Text Block] Federal Investment Income, Operating, Federal Tax Expense (Benefit), Current Investment Income, Operating, Federal Tax Expense (Benefit), Current Related Party [Axis] Related and Nonrelated Parties [Axis] Investment company, number of portfolio companies with annual third-party appraisal was obtained, reviewed and certified Investment Company, Number Of Portfolio Companies With Annual Third-Party Appraisal Was Obtained, Reviewed and Certified Investment Company, Number Of Portfolio Companies With Annual Third-Party Appraisal Was Obtained, Reviewed and Certified Repayments on Credit Facilities Repayments of Lines of Credit Document Period End Date Face amount Debt Instrument, Face Amount Debt instrument, term (in years) Debt Instrument, Term Interest rate (as a percent) Debt Instrument, Interest Rate, Effective Percentage Insight Borrower Corporation Insight Borrower Corporation [Member] Insight Borrower Corporation ITA Holdings Group, LLC ITA Holdings Group, LLC [Member] ITA Holdings Group, LLC Federal and state income and other tax expenses Investment Company, Federal And State Income And Other Tax Expense Investment Company, Federal And State Income And Other Tax Expense Entity Shell Company GS HVAM Intermediate, LLC GS HVAM Intermediate, LLC [Member] GS HVAM Intermediate, LLC Expected principal recovery percentage Measurement Input, Expected Principal Recovery Percentage [Member] Measurement Input, Expected Principal Recovery Percentage Cybermedia Technologies, LLC Cybermedia Technologies, LLC [Member] Cybermedia Technologies, LLC December 2025 Series A Notes December 2025 Series A Notes [Member] December 2025 Series A Notes Other (in dollars per share) Investment Company, Other, Per Share Investment Company, Other, Per Share Total income tax provision Investment Company, Income Tax Expense (Benefit) Investment Company, Income Tax Expense (Benefit) Document Fiscal Period Focus Incentive fee payable, capital-gain-based Incentive Fee Payable, Capital-Gain-Based Peer Group Issuers, Footnote Peer Group Issuers, Footnote [Text Block] O 2025 A2 Supplemental Dividends O 2025 A2 Supplemental Dividends [Member] O 2025 A2 Supplemental Dividends Total liabilities Liabilities Trading Symbol NET REALIZED GAIN (LOSS): Net Realized Gains (Losses) [Abstract] Net Realized Gains (Losses) Risk adjusted discount rate Measurement Input, Risk Adjusted Discount Rate [Member] Measurement Input, Risk Adjusted Discount Rate Doral Holdings, LLC Doral Holdings, LLC [Member] Doral Holdings, LLC Strike price (in dollars per share) Option Indexed to Issuer's Equity, Strike Price Company Selected Measure Name Company Selected Measure Name Sale of Stock [Domain] Sale of Stock [Domain] SI East, LLC SI East, LLC [Member] SI East, LLC Income Tax Disclosure [Abstract] Income Tax Disclosure [Abstract] Other Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Other Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Other CoreStack, Inc. CoreStack, Inc. [Member] CoreStack, Inc. MoneyThumb Acquisition, LLC MoneyThumb Acquisition, LLC [Member] MoneyThumb Acquisition, LLC Net realized gain (loss) (in dollars per share) Investment Company, Net Realized Gain (Loss) On Investment, Per Share Investment Company, Net Realized Gain (Loss) On Investment, Per Share Financial Instrument Performance Status [Axis] Financial Instrument Performance Status [Axis] Commitment fee (as a percentage) Line of Credit Facility, Commitment Fee Percentage Credit Facility [Domain] Credit Facility [Domain] CASH FLOWS FROM OPERATING ACTIVITIES Cash Provided by (Used in) Operating Activity, Including Discontinued Operation [Abstract] Dividends paid, per share (in dollars per share) Common Stock, Dividends, Per Share, Cash Paid Estimated taxable income Investment Company, Tax Basis, Net Income (Loss) Attributable To Parent, Estimated Investment Company, Tax Basis, Net Income (Loss) Attributable To Parent, Estimated Equity Valuation Assumption Difference, Footnote Equity Valuation Assumption Difference, Footnote [Text Block] Line of Credit Facility [Table] Line of Credit Facility [Table] Schedule of Investment Income Investment Income [Table Text Block] Health Care Providers & Services Health Care Providers & Services [Member] Health Care Providers & Services Dividend payable Dividend payable to MSCC and its subsidiaries Dividends Payable Schedule of Share-Based Compensation Arrangements by Share-Based Payment Award [Table] Schedule of Share-Based Compensation Arrangements by Share-Based Payment Award [Table] Interest and dividend receivable Dividend and Interest Receivable Other G&A expenses Other General and Administrative Expense Schedule of Changes in Fair Value of Main Street’s Level 3 Portfolio Investments Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block] Connect Telecommunications Solutions Holdings, Inc. Connect Telecommunications Solutions Holdings, Inc. [Member] Connect Telecommunications Solutions Holdings, Inc. Investment Company, Financial Highlights [Roll Forward] Investment Company, Financial Highlights [Roll Forward] Secured Revolving Promissory Note Secured Revolving Promissory Note [Member] Secured Revolving Promissory Note Award Timing Predetermined Award Timing Predetermined [Flag] NuStep, LLC NuStep, LLC [Member] NuStep, LLC Schedule of Summarized Dividend Reinvestment Plan Information Schedule of Summarized Dividend Reinvestment Plan Information [Table Text Block] Schedule of Summarized Dividend Reinvestment Plan Information DTE Enterprises, LLC DTE Enterprises, LLC [Member] DTE Enterprises, LLC Adjustment To PEO Compensation, Footnote Adjustment To PEO Compensation, Footnote [Text Block] Share‑based compensation APIC, Share-Based Payment Arrangement, Increase for Cost Recognition Quoted Prices in Active Markets for Identical Assets (Level 1) Fair Value, Inputs, Level 1 [Member] Middle Market portfolio investments Middle Market Portfolio [Member] Middle Market Portfolio Fair Value of Financial Instruments Fair Value of Financial Instruments, Policy [Policy Text Block] Summary of Investment Holdings [Line Items] Summary of Investment Holdings [Line Items] Student Resource Center, LLC Student Resource Center, LLC [Member] Student Resource Center, LLC Book income and tax income differences, including debt origination, structuring fees, dividends, realized gains and changes in estimates Investment Company, Tax Basis, Book Income and Tax Income Differences, Increase (Decrease) In Taxable Income Investment Company, Tax Basis, Book Income and Tax Income Differences, Increase (Decrease) In Taxable Income Waiver of incentive fees Investment Company, Expense, after Reduction of Fee Waiver and Reimbursement Plan Name [Domain] Plan Name [Domain] Scenario [Domain] Scenario [Domain] Datacom, LLC Datacom, LLC [Member] Datacom, LLC Concentration Risk Type [Domain] Concentration Risk Type [Domain] Amount of debt outstanding Related Party Transaction, Amount of Debt Outstanding Related Party Transaction, Amount of Debt Outstanding Fair Value Disclosures [Abstract] Containers & Packaging Containers & Packaging [Member] Containers & Packaging Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Brewer Crane Holdings, LLC Brewer Crane Holdings, LLC [Member] Brewer Crane Holdings, LLC Total dividends Payments of Ordinary Dividends, Common Stock Expiration Date Trading Arrangement Expiration Date Electrical Equipment Electrical Equipment [Member] Electrical Equipment Margin Effective Period Two Margin Effective Period Two [Member] Margin Effective Period Two Food & Staples Retailing Food & Staples Retailing [Member] Food & Staples Retailing Cash and cash equivalents, Fair Value Cash and Cash Equivalents, Fair Value Disclosure December 2025 Notes December 2025 Notes [Member] December 2025 Notes Affiliated Entity Affiliated Entity [Member] Aggregate Pension Adjustments Service Cost Aggregate Pension Adjustments Service Cost [Member] Proceeds from public offering of common stock, net of offering costs Proceeds from Issuance of Common Stock NET INVESTMENT INCOME Investment Income, Operating, after Expense and Tax VVS Holdco LLC VVS Holdco, LLC [Member] VVS Holdco, LLC Internet & Catalog Retail Internet & Catalog Retail [Member] Internet & Catalog Retail June 2027 Notes June 2027 Notes [Member] June 2027 Notes Related Party Transaction [Axis] Related Party Transaction [Axis] Current tax expense (benefit): Investment Tax Expense (Income), Current [Abstract] Investment Tax Expense (Income), Current BDB Holdings, LLC BDB Holdings, LLC [Member] BDB Holdings, LLC Investments in and Advances to Affiliates [Table] Investments in and Advances to Affiliates [Table] Hotels, Restaurants & Leisure Hotels, Restaurants & Leisure [Member] Hotels, Restaurants & Leisure DEBT Debt Disclosure [Text Block] Scenario [Axis] Scenario [Axis] U.S. TelePacific Corp. U.S. TelePacific Corp. [Member] U.S. TelePacific Corp. Deferred financing costs (net of accumulated amortization of $19,112 and $17,601, respectively) Deferred financing costs (net of accumulated amortization of $4,056 and $3,314, respectively) Debt Issuance Costs, Net PEO Actually Paid Compensation Amount PEO Actually Paid Compensation Amount Taxable income earned in prior year and carried forward for distribution in current year Investment Company, Tax Basis, Taxable Income Earned in Prior Year and Carried Forward for Distribution in Current Year Investment Company, Tax Basis Reconciliation, Taxable Income Earned in Prior Year and Carried Forward for Distribution in Current Year Third-party quote Measurement Input, Third-Party Quote [Member] Measurement Input, Third-Party Quote Channel Partners Intermediateco, LLC Channel Partners Intermediateco, LLC [Member] Channel Partners Intermediateco, LLC Jensen Jewelers of Idaho, LLC Jensen Jewelers of Idaho, LLC [Member] Jensen Jewelers of Idaho, LLC Southwest US Southwest Region [Member] Debt instrument, interest rate, stated (as a percent) Debt Instrument, Interest Rate, Stated Percentage Total net assets Balance as of beginning of period Balance as of ending of period Equity NAV as of the end of the period Equity, Attributable to Parent Investment Company, Nonconsolidated Subsidiary [Table] Investment Company, Nonconsolidated Subsidiary [Table] Gulf Manufacturing, LLC Gulf Manufacturing, LLC [Member] Gulf Manufacturing, LLC Sale of stock, shares not yet settled (in shares) Sale Of Stock, Shares Not Yet Settled Sale Of Stock, Shares Not Yet Settled ASSETS ASSETS Assets [Abstract] EBITDA multiple Measurement Input, EBITDA Multiple [Member] CenterPeak Holdings, LLC CenterPeak Holdings, LLC [Member] CenterPeak Holdings, LLC MSMF Main Street Mezzanine Fund, LP [Member] Main Street Mezzanine Fund, LP Airo Purchaser, Inc. Airo Purchaser, Inc. [Member] Airo Purchaser, Inc. Insider Trading Policies and Procedures [Line Items] Investment, Issuer Affiliation [Domain] Investment, Issuer Affiliation [Domain] Non-accrual Status Nonperforming Financial Instruments [Member] Roof Opco, LLC Roof Opco, LLC [Member] Roof Opco, LLC Ziegler’s NYPD, LLC Ziegler’s NYPD, LLC [Member] Ziegler’s NYPD, LLC Deferred taxes Deferred Income Tax Expense (Benefit) Shares outstanding as of the end of the period (in shares) Investment Company, Common Stock, Shares Outstanding Investment Company, Common Stock, Shares Outstanding Variable Rate Component [Domain] Variable Rate Component [Domain] Variable Rate Component [Domain] MSC Income Fund, Inc. MSC Income Fund, Inc. [Member] MSC Income Fund, Inc. Number of operating segments Number of Operating Segments Specialized Aviation Holdings, LLC Specialized Aviation Holdings, LLC [Member] Specialized Aviation Holdings, LLC Entity Central Index Key Robbins Bros. Jewelry, Inc. Robbins Bros. Jewelry, Inc. [Member] Robbins Bros. Jewelry, Inc. Equity [Abstract] Dividends or Other Earnings Paid on Equity Awards not Otherwise Reflected in Total Compensation for Covered Year Dividends or Other Earnings Paid on Equity Awards not Otherwise Reflected in Total Compensation for Covered Year [Member] LKCM Headwater Investments LKCM Headwater Investments [Member] LKCM Headwater Investments Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Schedule of Investments [Line Items] Schedule of Investments [Line Items] Dividend Revenue Recognition, Dividends [Policy Text Block] Schedule of Net Investment Income Related Taxes Schedule of Components of Income Tax Expense (Benefit) [Table Text Block] Accretion of unearned income Accretion of Unearned Income Accretion of Unearned Income Total net unrealized appreciation (depreciation) Net unrealized (appreciation) depreciation Total net unrealized appreciation (depreciation) Amount of Unrealized Gain/(Loss) Debt and Equity Securities, Unrealized Gain (Loss) Debt instrument, basis spread on variable rate (as a percent) Debt Instrument, Basis Spread on Variable Rate Brainworks Software, LLC Brainworks Software, LLC [Member] Brainworks Software, LLC Variable Rate [Domain] Variable Rate [Domain] Restricted Stock Restricted Stock [Member] Bridge Capital Solutions Corporation Bridge Capital Solutions Corporation [Member] Bridge Capital Solutions Corporation All Individuals All Individuals [Member] Mills Fleet Farm Group, LLC Mills Fleet Farm Group, LLC [Member] Mills Fleet Farm Group, LLC Investment, Issuer Name [Domain] Investment, Issuer Name [Domain] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] Share-based payment arrangement, nonvested award, cost not yet recognized, period for recognition (in years) Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition Annual revenues Investments, Annual Revenues Per Company Investments, Annual Revenues Per Company Total net realized gain Net realized gain Total net realized loss Amount of Realized Gain/(Loss) Debt and Equity Securities, Realized Gain (Loss) Interest rate (as a percent) Investment, Index Based Floating Interest Rate Investment, Index Based Floating Interest Rate Direct Marketing Solutions, Inc. Direct Marketing Solutions, Inc. [Member] Direct Marketing Solutions, Inc. O 2026 M8 Dividends O 2026 M8 Dividends [Member] O 2026 M8 Dividends Digital Products Holdings LLC Digital Products Holdings LLC [Member] Digital Products Holdings LLC Statement [Line Items] Statement [Line Items] Total assets Assets JTI Electrical & Mechanical, LLC JTI Electrical & Mechanical, LLC [Member] JTI Electrical & Mechanical, LLC Interest Interest Interest Expense, Operating Debt instrument, issuance price (as a percent) Debt Instrument, Issuance Price, Percentage Debt Instrument, Issuance Price, Percentage Industry Sector [Axis] Industry Sector [Axis] August 2028 Notes August 2028 Notes [Member] August 2028 Notes O 2025 Q2 Regular Dividends O 2025 Q2 Regular Dividends [Member] O 2025 Q2 Regular Dividends Excise tax expense Excise Investment Company, Excise Tax Expense SHARE-BASED COMPENSATION Share-Based Payment Arrangement [Text Block] PEO PEO [Member] Federal Realized Gain (Loss), Investment And Derivative, Operating, Federal Tax Expense (Benefit), Current Realized Gain (Loss), Investment And Derivative, Operating, Federal Tax Expense (Benefit), Current Management and service fees, catch up feature rate (as a percent) Management and Service Fees, Rate HDC/HW Intermediate Holdings HDC/HW Intermediate Holdings [Member] HDC/HW Intermediate Holdings Auria Space, LLC Auria Space, LLC [Member] Auria Space, LLC Nello Industries Investco, LLC Nello Industries Investco, LLC [Member] Nello Industries Investco, LLC Forgone Recovery due to Violation of Home Country Law, Amount Forgone Recovery due to Violation of Home Country Law, Amount Total Undistributed Earnings Retained Earnings [Member] Total allocated expenses Total expenses Operating Expenses Money Market Funds Money Market Funds [Member] Revolving Credit Facility Credit Facility Revolving Credit Facility [Member] Fair Value Measurement Fair Value Measurement, Policy [Policy Text Block] Net increase in net assets resulting from operations (in dollars per share) Investment Company, Investment Income (Loss) from Operations, Per Share Communications Equipment Communications Equipment [Member] Communications Equipment Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Common stock, shares outstanding (in shares) Balance as of beginning of period (in shares) Balance as of ending of period (in shares) Common Stock, Shares, Outstanding Award Timing Disclosures [Line Items] Federal Realized Gain (Loss), Investment And Derivative, Operating, Deferred Federal Tax Expense (Benefit) Realized Gain (Loss), Investment And Derivative, Operating, Deferred Federal Tax Expense (Benefit) Amortization of directors’ deferred compensation Adjustments To Additional Paid In Capital, Amortization Of Directors’ Deferred Compensation Adjustments To Additional Paid In Capital, Amortization Of Directors’ Deferred Compensation Kickhaefer Manufacturing Company, LLC Kickhaefer Manufacturing Company, LLC [Member] Kickhaefer Manufacturing Company, LLC Second lien debt Debt Securities, Second Lien [Member] Debt Securities, Second Lien Bettercloud, Inc. Bettercloud, Inc. [Member] Bettercloud, Inc. Computer Data Source, LLC Computer Data Source, LLC [Member] Computer Data Source, LLC Software Software [Member] Software Share-Based Payment Arrangement [Abstract] South Coast Terminals Holdings, LLC South Coast Terminals Holdings, LLC [Member] South Coast Terminals Holdings, LLC Total investment return Investment Company, Total Return, Market Value AAC Holdings, Inc. AAC Holdings, Inc. [Member] AAC Holdings, Inc. Equity Awards Adjustments, Footnote Equity Awards Adjustments, Footnote [Text Block] Interest payable Increase (Decrease) in Interest Payable, Net Schedule of Information from External Investment Manager Investment Company, Nonconsolidated Subsidiary, Summarized Financial Information [Table Text Block] Investment, Issuer Name [Axis] Investment, Issuer Name [Axis] Value of shares issued pursuant to the dividend reinvestment plan Stock Issued Textiles, Apparel & Luxury Goods Textiles, Apparel & Luxury Goods [Member] Textiles, Apparel & Luxury Goods NAPCO Precast, LLC NAPCO Precast, LLC [Member] NAPCO Precast, LLC Title of Individual [Axis] Title and Position [Axis] Sale of Stock [Axis] Sale of Stock [Axis] Schedule of Dividend Information Dividends Declared [Table Text Block] Revenue Recovery Holdings, LLC Revenue Recovery Holdings, LLC [Member] Revenue Recovery Holdings, LLC Dividend income Dividend income Investment Income, Dividend Related Party Transaction [Domain] Related Party Transaction [Domain] Rule 10b5-1 Arrangement Adopted Rule 10b5-1 Arrangement Adopted [Flag] Investments at fair value: Fair value Total Level 3 investments Beginning balance Ending balance Investment Owned, Fair Value Equity investments Equity Equity Securities [Member] BP Loenbro Holdings Inc. BP Loenbro Holdings Inc. [Member] BP Loenbro Holdings Inc. OnAsset Intelligence, Inc. OnAsset Intelligence, Inc. [Member] OnAsset Intelligence, Inc. Number of portfolio companies Investment Company, Number Of Portfolio Companies Investment Company, Number Of Portfolio Companies Northeast Region and Canada Northeast Region and Canada [Member] Northeast Region and Canada Common stock, shares issued (in shares) Common Stock, Shares, Issued Beginning balance Ending balance Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value Consolidated Schedule of Investments in and Advances to Affiliates Investments in and Advances to Affiliates, Schedule of Investments [Text Block] Cash exceeded federal deposit insurance corporation insurance protection levels Cash, Uninsured Amount Product and Service [Domain] Product and Service [Domain] Deferred tax liability, net Deferred Income Tax Liabilities, Net Compensation Actually Paid vs. Other Measure Compensation Actually Paid vs. Other Measure [Text Block] Trading Companies & Distributors Trading Companies & Distributors [Member] Trading Companies & Distributors Termination Date Trading Arrangement Termination Date O 2026 Q3 Including Supplemental Dividends O 2026 Q3 Including Supplemental Dividends [Member] O 2026 Q3 Including Supplemental Dividends ATS Operating, LLC ATS Operating, LLC [Member] ATS Operating, LLC State and other Realized Gain (Loss), Investment And Derivative, Operating, Deferred State And Other Tax Expense (Benefit) Realized Gain (Loss), Investment And Derivative, Operating, Deferred State And Other Tax Expense (Benefit) Subsequent Events [Abstract] Kennedy Fab HoldCo, LLC Kennedy Fab HoldCo, LLC [Member] Kennedy Fab HoldCo, LLC Fair Value, Recurring and Nonrecurring [Table] Fair Value, Recurring and Nonrecurring [Table] Contractual obligation, number of additional investments, investment period expired with remaining commitments restricted for fund expenses or follow on investments in existing portfolio companies Investment Company, Number Of Additional Investments, Commitments Restricted For Fund Expenses Or Follow On Investments In Existing Portfolio Investment Company, Number Of Additional Investments, Commitments Restricted For Fund Expenses Or Follow On Investments In Existing Portfolio Compensation Actually Paid vs. Total Shareholder Return Compensation Actually Paid vs. Total Shareholder Return [Text Block] Net Realized Gains or Losses and Net Unrealized Appreciation or Depreciation Net Realized Gains or Losses And Net Unrealized Appreciation or Depreciation [Policy Text Block] Net Realized Gains or Losses And Net Unrealized Appreciation or Depreciation SPAU Holdings, LLC SPAU Holdings, LLC [Member] SPAU Holdings, LLC RFG AcquireCo, LLC RFG AcquireCo, LLC [Member] RFG AcquireCo, LLC Transfers Into (Out of) Level 3 Hierarchy Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers, Net Fair Value as of Grant Date Award Grant Date Fair Value Percentage of total investment come, attributable to noncash cumulative dividend income (as a percent) Investment Company, Percentage Of Total Investment Income, Attributable To Noncash Cumulative Dividend Income Investment Company, Percentage Of Total Investment Income, Attributable To Noncash Cumulative Dividend Income Pay vs Performance Disclosure, Table Pay vs Performance [Table Text Block] Xenon Arc, Inc. Xenon Arc, Inc. [Member] Xenon Arc, Inc. Arrangement Duration Trading Arrangement Duration American Health Staffing Group, Inc. American Health Staffing Group, Inc. [Member] American Health Staffing Group, Inc. Entity Address, Postal Zip Code Entity Registrant Name SBIC debentures SBIC debentures SBIC Debentures [Member] SBIC Debentures WACC Measurement Input, Weighted-Average Cost Of Capital [Member] Measurement Input, Weighted-Average Cost Of Capital Insider Trading Policies and Procedures Not Adopted Insider Trading Policies and Procedures Not Adopted [Text Block] Total revenues before waivers Revenues Forgone Recovery due to Expense of Enforcement, Amount Forgone Recovery due to Expense of Enforcement, Amount GFG Group, LLC GFG Group, LLC. [Member] GFG Group, LLC. Vesting period (in years) Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Period GradeEight Corp. GradeEight Corp. [Member] GradeEight Corp. Award Type [Domain] Award Type [Domain] MSCC Funding I, LLC MSCC Funding I, LLC [Member] MSCC Funding I, LLC FAIR VALUE HIERARCHY FOR INVESTMENTS—PORTFOLIO COMPOSITION Fair Value Disclosures [Text Block] Significant Unobservable Inputs (Level 3) Fair Value, Inputs, Level 3 [Member] Media Media [Member] Media Dividends Declared But Not Yet Paid Dividends Declared But Not Yet Paid [Member] Dividends Declared But Not Yet Paid Share price (in dollars per share) Geographical [Axis] Geographical [Axis] EnCap Energy Fund Investments EnCap Energy Fund Investments [Member] EnCap Energy Fund Investments Investment, Issuer Affiliation [Axis] Investment, Issuer Affiliation [Axis] Legal Entity [Axis] Total Interest Expense Interest Expense, Debt West US West Region [Member] Fee Income Management and Investment Advisory Fees, Policy [Policy Text Block] Deferred Compensation Plan Postemployment Benefit Plans, Policy [Policy Text Block] Air Freight & Logistics Air Freight & Logistics [Member] Air Freight & Logistics CASH AND CASH EQUIVALENTS AS OF BEGINNING OF PERIOD CASH AND CASH EQUIVALENTS AS OF END OF PERIOD Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Continuing Operation Boccella Precast Products LLC Boccella Precast Products LLC [Member] Boccella Precast Products LLC O 2026 Q3 Dividends O 2026 Q3 Dividends [Member] O 2026 Q3 Dividends Tax credit carryforward Investment Company, Distributable Earnings (Loss), Accumulated Capital Loss Carryforward Non-NEOs Non-NEOs [Member] Jackmont Hospitality, Inc. Jackmont Hospitality, Inc. [Member] Jackmont Hospitality, Inc. KMS, LLC KMS, LLC [Member] KMS, LLC External Investment Manager External Investment Manager [Member] External Investment Manager Schedule of Debt and Average Amount of Total Borrowings Outstanding and Weighted-Overall Average Effective Interest Rate Schedule of Debt [Table Text Block] Net investment income taxes Net Investment Income Tax Expense (Benefit) [Abstract] Net Investment Income Tax Expense (Benefit) Long-Term Debt, Type [Domain] Long-Term Debt, Type [Domain] Schedule of Restricted Stock Issued Disclosure of Share-Based Compensation Arrangements by Share-Based Payment Award [Table Text Block] Statistical Measurement [Axis] Statistical Measurement [Axis] Management and service fees (as a percent) Management and Service Fees, Base Rate Hawk Ridge Systems, LLC Hawk Ridge Systems, LLC [Member] Hawk Ridge Systems, LLC O 2026 Q2 Supplemental Dividends O 2026 Q2 Supplemental Dividends [Member] O 2026 Q2 Supplemental Dividends Award Type [Axis] Award Type [Axis] IT Services IT Services [Member] IT Services FCC Intermediate Holdco, LLC FCC Intermediate Holdco, LLC [Member] FCC Intermediate Holdco, LLC Named Executive Officers, Footnote Named Executive Officers, Footnote [Text Block] Amount of Interest, Fees or Dividends Credited to Income Interest, Fees and Dividend Income, Securities, Operating Interest, Fees and Dividend Income, Securities, Operating Total undistributed earnings Total undistributed earnings Retained Earnings (Accumulated Deficit) CQ Fluency, LLC CQ Fluency, LLC [Member] CQ Fluency, LLC Investment Owned, At Fair Value Investment Owned, At Fair Value [Member] Investment Owned, At Fair Value Product and Service [Axis] Product and Service [Axis] Northeast US Northeast Region [Member] ASC Interests, LLC ASC Interests, LLC [Member] ASC Interests, LLC Summary of Investment Holdings [Table] Investment Holdings [Table] Awards Close in Time to MNPI Disclosures Awards Close in Time to MNPI Disclosures [Table] Common Stock Common Stock [Member] Harris Preston Fund Investments Harris Preston Fund Investments Two [Member] Harris Preston Fund Investments Two Other Non-U.S. Non-US [Member] Current tax expense (benefit): Current Federal, State and Local, Tax Expense (Benefit) [Abstract] Batjer TopCo, LLC Batjer TopCo, LLC [Member] Batjer TopCo, LLC Obra Capital, Inc. Obra Capital, Inc. [Member] Obra Capital, Inc. Principle Environmental, LLC Principle Environmental, LLC [Member] Principle Environmental, LLC Concentration Risk Benchmark [Axis] Concentration Risk Benchmark [Axis] Accrued incentive fees on capital gains Increase (Decrease) in Incentive Fee Payable Total liabilities and net assets Liabilities and Equity Ignite Visibility LLC Ignite Visibility LLC [Member] Ignite Visibility LLC Employee Stock Option Share-Based Payment Arrangement, Option [Member] New Investments Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases O 2026 Q3 Supplemental Dividends O 2026 Q3 Supplemental Dividends [Member] O 2026 Q3 Supplemental Dividends Additional 402(v) Disclosure Additional 402(v) Disclosure [Text Block] Asset Class [Axis] Asset Class [Axis] Related Party [Domain] Related and Nonrelated Parties [Domain] Debt instrument, number of lenders Debt Instrument, Number Of Lenders Debt Instrument, Number Of Lenders Tabular List, Table Tabular List [Table Text Block] Additional paid-in capital Contributed capital Additional Paid in Capital At-The-Market Offerings At-The-Market Offerings [Member] At-The-Market Offerings Name Awards Close in Time to MNPI Disclosures, Individual Name Investment, Identifier [Axis] Investment, Identifier [Axis] Year-end Fair Value of Equity Awards Granted in Covered Year that are Outstanding and Unvested Year-end Fair Value of Equity Awards Granted in Covered Year that are Outstanding and Unvested [Member] Market approach Valuation, Market Approach [Member] Sale of stock, price per share (in dollars per share) Sale of Stock, Price Per Share Ratio of operating expenses to average NAV Investment Company, Operating Expenses Ratio Investment Company, Operating Expenses Ratio Charps, LLC Charps, LLC [Member] Charps, LLC Percentage of portfolio with annual third-party appraisal was obtained, reviewed and certified (as a percent) Investment Company, Percentage of Portfolio With Annual Third-Party Appraisal Was Obtained, Reviewed and Certified Investment Company, Percentage of Portfolio With Annual Third-Party Appraisal Was Obtained, Reviewed and Certified Adjustment to Compensation: Adjustment to Compensation [Axis] Income tax provision on net realized gain (loss) and net unrealized appreciation (in dollars per share) Investment​ Company, Income Tax Benefit (Provision) On Net Realized Gain And Net Unrealized Appreciation, ​​Per​ Share Investment​ Company, Income Tax Benefit (Provision) On Net Realized Gain And Net Unrealized Appreciation, ​​Per​ Share NET INCREASE IN NET ASSETS RESULTING FROM OPERATIONS PER SHARE—DILUTED (in dollars per share) Investment Company, Investment Income (Loss) from Operations, Per Share, Per Diluted Share Investment Company, Investment Income (Loss) from Operations, Per Share, Per Diluted Share Schedule of Accrued Incentive Fees on Capital Gains Schedule Of Accrued Incentive Fees On Capital Gains [Table Text Block] Schedule Of Accrued Incentive Fees On Capital Gains Dividends Payable [Line Items] Dividends Payable [Line Items] Dividends Payable [Table] Dividends Payable [Table] Rule 10b5-1 Arrangement Terminated Rule 10b5-1 Arrangement Terminated [Flag] Aggregate Erroneous Compensation Amount Aggregate Erroneous Compensation Amount Interest paid Interest Paid, Excluding Capitalized Interest, Operating Activity Televerde, LLC Televerde, LLC [Member] Televerde, LLC Credit Facility [Axis] Credit Facility [Axis] Island Pump and Tank, LLC Island Pump and Tank, LLC [Member] Island Pump and Tank, LLC Spring Engineering Holdings, LLC Spring Engineering Holdings, LLC [Member] Spring Engineering Holdings, LLC Name Measure Name Pay vs Performance Disclosure [Line Items] Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Debt Instrument [Line Items] Debt Instrument [Line Items] Additional Paid-In Capital Additional Paid-in Capital [Member] SOFR Adjustment Spread SOFR Adjustment Spread [Member] SOFR Adjustment Spread Name Trading Arrangement, Individual Name Share-based payment arrangement, nonvested award, excluding option, cost not yet recognized, amount Share-Based Payment Arrangement, Nonvested Award, Excluding Option, Cost Not yet Recognized, Amount Investment valuation related taxes Investment Tax Expense (Income) [Abstract] Investment Tax Expense (Income) Cash and cash equivalents Cash and cash equivalent, Cost Cash and cash equivalents Cash and Cash Equivalent Company Selected Measure Amount Company Selected Measure Amount UniTek Global Services, Inc. UniTek Global Services, Inc. [Member] UniTek Global Services, Inc. SOFR Secured Overnight Financing Rate (SOFR) [Member] Titan Meter Midco Corp. Titan Meter Midco Corp. [Member] Titan Meter Midco Corp. Nearshore AcquireCo, LLC Nearshore AcquireCo, LLC [Member] Nearshore AcquireCo, LLC Net unrealized (appreciation) depreciation Investment Company, Tax Basis, Unrealized (Gain) Loss, Not Currently (Taxable) Deductible Investments Investments, Per Company Investments, Per Company Non-PEO NEO Non-PEO NEO [Member] Moffitt Holdings, LLC Moffitt Holdings, LLC [Member] Moffitt Holdings, LLC EXPENSES: EXPENSES: Interest and Debt Expense [Abstract] Subsidiary, Sale of Stock [Line Items] Subsidiary, Sale of Stock [Line Items] Total net investment income tax provision Investment Income, Operating, Tax Expense (Benefit) Deferred tax expense (benefit): Deferred Tax Expense (Income) [Abstract] Deferred Tax Expense (Income) Award Timing Method Award Timing Method [Text Block] Accretive effect of stock offerings (issuing shares above NAV per share) (in dollars per share) Investment Company, Effect of Stock Offerings, Per Share Investment Company, Effect of Stock Offerings, Per Share Net increase in cash and cash equivalents Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Period Increase (Decrease), Including Exchange Rate Effect and Discontinued Operation Forecast Forecast [Member] Forgone Recovery, Explanation of Impracticability Forgone Recovery, Explanation of Impracticability [Text Block] Trantech Radiator Topco, LLC Trantech Radiator Topco, LLC [Member] Trantech Radiator Topco, LLC MSC Income MSC Income [Member] MSC Income NET INCREASE IN NET ASSETS RESULTING FROM OPERATIONS Net increase in net assets resulting from operations Net increase in net assets resulting from operations Net Income (Loss) Attributable to Parent MonitorUS Holding, LLC MonitorUS Holding, LLC [Member] MonitorUS Holding, LLC Long-Term Debt, Type [Axis] Long-Term Debt, Type [Axis] Erroneous Compensation Analysis Erroneous Compensation Analysis [Text Block] Investments Investments [Member] Restatement Determination Date: Restatement Determination Date [Axis] KBK Industries, LLC KBK Industries, LLC [Member] KBK Industries, LLC June 2027 Notes, Additional June 2027 Notes, Additional [Member] June 2027 Notes, Additional Management fee income Management Service, Base [Member] Condensed Income Statements, Captions [Line Items] Condensed Income Statements, Captions [Line Items] Condensed Balance Sheet Statements, Captions [Line Items] Condensed Balance Sheet Statements, Captions [Line Items] External Investment Manager External Investment Manager Investments [Member] External Investment Manager Investments Proceeds from sales and return of capital of equity investments in portfolio companies Proceeds From Sales And Return Of Capital Of Equity Investments In Portfolio Companies Proceeds From Sales And Return Of Capital Of Equity Investments In Portfolio Companies Other direct G&A expenses Other General and Administrative Expense, Direct Other General and Administrative Expense, Direct Southeast US Southeast Region [Member] California Splendor Holdings LLC California Splendor Holdings LLC [Member] California Splendor Holdings LLC Distributors Distributors [Member] Distributors MCT Purchaserco Holding Inc. MCT Purchaserco Holding Inc. [Member] MCT Purchaserco Holding Inc. Pension Benefits Adjustments, Footnote Pension Benefits Adjustments, Footnote [Text Block] Statistical Measurement [Domain] Statistical Measurement [Domain] Pro-Max Restoration & Paint, LLC Pro-Max Restoration & Paint, LLC [Member] Pro-Max Restoration & Paint, LLC Document Fiscal Year Focus CGMS Parent LLC CGMS Parent LLC [Member] CGMS Parent LLC Number of Shares Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] Share purchase (repurchase) program, number of active plans Share Purchase (Repurchase) Program, Number Of Active Plans Share Purchase (Repurchase) Program, Number Of Active Plans State and other Investment Income, Operating, State And Other Tax Expense (Benefit), Current Investment Income, Operating, State And Other Tax Expense (Benefit), Current Common stock, $0.01 par value per share (150,000,000 shares authorized; 93,354,166 and 89,834,849 shares issued and outstanding, 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OUTSTANDING—BASIC (in shares) Weighted Average Number of Shares Outstanding, Basic Funded commitments Related Party Transaction, Purchases from Related Party OnPoint Industrial Services, LLC OnPoint Industrial Services, LLC [Member] OnPoint Industrial Services, LLC Infinity X1 Holdings, LLC Infinity X1 Holdings, LLC [Member] Infinity X1 Holdings, LLC Fair Value, by Balance Sheet Grouping [Table] Fair Value, by Balance Sheet Grouping [Table] Victory Energy Operations, LLC Victory Energy Operations, LLC [Member] Victory Energy Operations, LLC Dynamic Communities, LLC Dynamic Communities, LLC [Member] Dynamic Communities, LLC Advisory Agreement, Previous Advisory Agreement, Previous [Member] Advisory Agreement, Previous Fuse, LLC Fuse, LLC [Member] Fuse, LLC Schedule of Investments [Abstract] Schedule of Investments [Abstract] Investment Company, Nonconsolidated Subsidiary [Line Items] Investment Company, Nonconsolidated Subsidiary [Line Items] Median Median [Member] Equity Warrant Equity 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Rug Doctor, LLC. [Member] Rug Doctor, LLC. 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Adjustments, Excluding Value Reported in Compensation Table Equity Awards Adjustments, Excluding Value Reported in the Compensation Table [Member] COMMON STOCK Equity [Text Block] Legacy Swim Group Legacy Swim Group [Member] Legacy Swim Group Security Exchange Name Investment, accruing income fixed cash rate Investment, Accruing Income Fixed Cash Rate Investment, Accruing Income Fixed Cash Rate Internet Software & Services Internet Software & Services [Member] Internet Software & Services Valuation Approach and Technique [Axis] Valuation Approach and Technique [Axis] O 2026 A2 Supplemental Dividends O 2026 A2 Supplemental Dividends [Member] O 2026 A2 Supplemental Dividends O 2026 Q4 Dividends O 2026 Q4 Dividends [Member] O 2026 Q4 Dividends Restricted stock authorized under the plan (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Authorized Segments Segment Reporting, Policy [Policy Text Block] Investments in and Advances to Affiliates, 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American Glass Services Acquisition, LLC AGS American Glass Services Acquisition, LLC [Member] AGS American Glass Services Acquisition, LLC Schedule of Investments [Table] Schedule of Investments [Table] Additional debenture capacity Debt Instrument, Additional Carrying Amount Debt Instrument, Additional Carrying Amount Non-cash financing activities: Noncash Investing and Financing Items [Abstract] Dividends paid from net investment income (in dollars per share) Investment Company, Dividend Distribution to Shareholders, Per Share Investment Company, Dividend Distribution to Shareholders, Per Share Outstanding Balance Long-Term Debt, Gross Condensed Income Statement [Table] Condensed Income Statement [Table] Debt Debt investments Debt Securities [Member] Asset Class [Domain] Asset Class [Domain] Related Party Transactions [Abstract] Tobacco Tobacco [Member] Tobacco Deferred Financing Costs Debt, Policy [Policy Text Block] Compensation Amount Outstanding Recovery Compensation Amount Individual: Individual [Axis] WEIGHTED-AVERAGE SHARES OUTSTANDING—DILUTED (in shares) Weighted Average Number of Shares Outstanding, Diluted Entity Emerging Growth Company Related Party Transaction [Line Items] Related Party Transaction [Line Items] Percentage of loans with variable rate floors (as a percent) Investment Company, Percentage Of Loans With Variable Rate Floors Investment Company, Percentage Of Loans With Variable Rate Floors Underlying Security Market Price Change Underlying Security Market Price Change, Percent Accrued incentive fees Accrued Incentive Fees Accrued Incentive Fees Proceeds from Credit Facilities Proceeds from Lines of Credit Cash equivalents Cash Equivalent, Money Market Fund, Carrying Value Flame King Holdings, LLC Flame King Holdings, LLC [Member] Flame King Holdings, LLC Condensed Balance Sheet Statement [Table] Condensed Balance Sheet Statement [Table] Accounts receivable from MSCC and its subsidiaries Other Receivables Corporate Facility Corporate Facility [Member] Corporate Facility April 2031 Notes April 2031 Notes [Member] April 2031 Notes Adams Publishing Group, LLC Adams Publishing Group, LLC [Member] Adams Publishing Group, LLC Pinnacle TopCo, LLC Pinnacle TopCo, LLC [Member] Pinnacle TopCo, LLC Bolder Panther Group, LLC Bolder Panther Group, LLC [Member] Bolder Panther Group, LLC Proceeds from public offering Proceeds from Issuance of Unsecured Debt Organization, Consolidation and Presentation of Financial Statements [Abstract] Debt instrument, credit spread adjustment (as a percent) Debt Instrument, Credit Spread Adjustment Debt Instrument, Credit Spread Adjustment Investment Company, Financial Highlights [Line Items] Investment Company, Financial Highlights [Line Items] Ratio of net investment income to average NAV Investment Company, Investment Income (Loss) Ratio EXTERNAL INVESTMENT MANAGER External Investment Manager [Text Block] External Investment Manager Nonvested beginning balance (in dollars per share) Nonvested 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2026 M9 Dividends Cumulative dividends Cumulative Dividends, Non-cash Cumulative Dividends, Non-cash Dividends to stockholders Dividends, Common Stock Isagenix International, LLC Isagenix International, LLC [Member] Isagenix International, LLC Commercial Services & Supplies Commercial Services & Supplies [Member] Commercial Services & Supplies Common stock, shares authorized (in shares) Common Stock, Shares Authorized Sale of stock, number of shares issued in transaction (in shares) Sale of Stock, Number of Shares Issued in Transaction Wash & Wax Systems LLC Wash & Wax Systems LLC [Member] Wash & Wax Systems LLC UPS Intermediate, LLC UPS Intermediate, LLC [Member] UPS Intermediate, LLC Dos Rios Partners Dos Rios Partners [Member] Dos Rios Partners Exercise Price Award Exercise Price Issuance of restricted stock, net of forfeited shares Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures Fair Value, Recurring Fair Value, Recurring [Member] Share repurchase program, authorized, amount Share Repurchase Program, Authorized, Amount Metalforming Holdings, LLC Metalforming Holdings, LLC [Member] Metalforming Holdings, LLC Investment Owned, At Cost Investment Owned, At Cost [Member] Investment Owned, At Cost Document Quarterly Report Year-over-Year Change in Fair Value of Equity Awards Granted in Prior Years That are Outstanding and Unvested Year-over-Year Change in Fair Value of Equity Awards Granted in Prior Years That are Outstanding and Unvested [Member] O 2026 M7 Dividends O 2026 M7 Dividends [Member] O 2026 M7 Dividends Vitesse Systems Vitesse Systems [Member] Vitesse Systems Accounts receivable - advisory clients Accounts Receivable, after Allowance for Credit Loss Measurement input Investment Company, Investment Owned, Measurement Input Investment, cost Cost Investment Owned, Cost Gross Additions Investments in and Advances to Affiliates, at Fair Value, Gross Additions Interest payable Interest payable Interest Payable Investment company, number of companies within portfolio excluded from EBITDA calculation Investment Company, Number of Companies Within Portfolio Excluded From EBITDA Calculation Investment Company, Number of Companies Within Portfolio Excluded From EBITDA Calculation Management fee to MSCC Management Fee Expense Unamortized debt discount Net Unamortized Debt Issuance Premiums (Costs/Discounts) Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net Awards Close in Time to MNPI Disclosures, Table Awards Close in Time to MNPI Disclosures [Table Text Block] FINANCIAL HIGHLIGHTS Investment Company, Financial Highlights [Text Block] Equity Component [Domain] Equity Component [Domain] Share purchase program, authorized, amount Share Purchase Program, Authorized, Amount Share Purchase Program, Authorized, Amount Gain (loss) included in earnings Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings Measurement 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Restatement does not require Recovery Restatement Does Not Require Recovery [Text Block] World Micro Holdings, LLC World Micro Holdings, LLC [Member] World Micro Holdings, LLC Microbe Formulas, LLC Microbe Formulas, LLC [Member] Microbe Formulas, LLC Insider Trading Policies and Procedures Adopted Insider Trading Policies and Procedures Adopted [Flag] Event Holdco, LLC Event Holdco, LLC [Member] Event Holdco, LLC Phantom Stock Units Phantom Share Units (PSUs) [Member] O 2026 A4 Life-To-Date Dividends O 2026 A4 Life-To-Date Dividends [Member] O 2026 A4 Life-To-Date Dividends IG Parent Corporation IG Parent Corporation [Member] IG Parent Corporation Chemicals Chemicals [Member] Chemicals COMMITMENTS AND CONTINGENCIES Commitments and Contingencies Disclosure [Text Block] Compensation Actually Paid vs. Net Income Compensation Actually Paid vs. Net Income [Text Block] PrimeFlight Aviation Services PrimeFlight Aviation Services [Member] PrimeFlight Aviation Services Clad-Rex Steel, LLC Clad-Rex Steel, LLC [Member] Clad-Rex Steel, LLC Weighted-Average Weighted Average [Member] All Adjustments to Compensation All Adjustments to Compensation [Member] Income Taxes Income Tax, Policy [Policy Text Block] Implus Footcare, LLC Implus Footcare, LLC [Member] Implus Footcare, LLC Net cash provided by (used in) operating activities Cash Provided by (Used in) Operating Activity, Including Discontinued Operation Diluted equity ownership (as a percent) Investment Company, Average Fully Diluted Equity Ownership, Percentage Investment Company, Average Fully Diluted Equity Ownership, Percentage Income Statement [Abstract] NET ASSETS NET ASSETS Equity, Attributable to Parent [Abstract] Document Transition Report Construction & Engineering Construction & Engineering [Member] Construction & Engineering Compensation Salary and Wage, Excluding Cost of Good and Service Sold Stock Appreciation Rights (SARs) Stock Appreciation Rights (SARs) [Member] FRG AcquireCo, LLC FRG AcquireCo, LLC [Member] FRG AcquireCo, LLC Watterson Brands, LLC Watterson Brands, LLC [Member] Watterson Brands, LLC Spread (as a percent) Spread Investment, Basis Spread, Variable Rate Proceeds from sales and repayments of debt investments in portfolio companies Proceeds From Sales And Repayments Of Debt Investments In Portfolio Companies Proceeds From Sales And Repayments Of Debt Investments In Portfolio Companies City Area Code Risk adjusted discount rate, outlier Measurement Input, Risk Adjusted Discount Rate, Outlier [Member] Measurement Input, Risk Adjusted Discount Rate, Outlier Face amount, additional issuance Debt Instrument, Face Amount, Additional Issuance Debt Instrument, Face Amount, Additional Issuance Geographic Concentration Risk Geographic Concentration Risk [Member] SUBSEQUENT EVENTS Subsequent Events [Text Block] UBM AcquireCo LLC UBM AcquireCo LLC [Member] UBM AcquireCo LLC Bluestem Brands, Inc. Bluestem Brands, Inc. [Member] Bluestem Brands, Inc. Estimated Fair Value Debt Instrument, Fair Value Disclosure Name Forgone Recovery, Individual Name Berry Aviation, Inc. Berry Aviation, Inc. [Member] Berry Aviation, Inc. Non-GAAP Measure Description Non-GAAP Measure Description [Text Block] Weighted-Average Grant-Date Fair Value Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract] NRP Jones, LLC NRP Jones, LLC [Member] NRP Jones, LLC GULF PACIFIC ACQUISITION, LLC GULF PACIFIC ACQUISITION, LLC [Member] GULF PACIFIC ACQUISITION, LLC Entity [Domain] Market value as of the end of the period (in dollars per share) Investment Company, Market Value, Per Share Share-Based Compensation Share-Based Payment Arrangement [Policy Text Block] Private Loan portfolio investments Private Loan Portfolio [Member] Private Loan Portfolio Margin Effective Period One Margin Effective Period One [Member] Margin Effective Period One Accounts payable and other liabilities Accounts payable and other liabilities to affiliates Accounts Payable and Other Accrued Liabilities Tedder Industries, LLC Tedder Industries, LLC [Member] Tedder Industries, LLC Net deferred tax liability Deferred Tax Liabilities, Net Public offering of common stock, net of offering costs (in shares) Stock Issued During Period, Shares, New Issues Cash and Cash Equivalents [Domain] Cash and Cash Equivalents [Domain] Unused capacity, commitment fee (as a percent) Related Party Transaction, Unused Capacity, Commitment Fee Percentage Related Party Transaction, Unused Capacity, Commitment Fee Percentage Principal Investment Owned, Balance, Principal Amount Share-based compensation Share‑based compensation Share-Based Payment Arrangement, Expense Number of investment managers Investment Company, Number Of Portfolio Investments, Investment Managers Investment Company, Number Of Portfolio Investments, Investment Managers Cash and Cash Equivalents Cash and Cash Equivalents, Policy [Policy Text Block] Fair Value Measurement Inputs and Valuation Techniques [Line Items] Fair Value Measurement Inputs and Valuation Techniques [Line Items] Granted (in dollars per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value Margin Effective Period [Axis] Margin Effective Period [Axis] Margin Effective Period Logix Acquisition Company, LLC Logix Acquisition Company, LLC [Member] Logix Acquisition Company, LLC Schedule of Taxable Income and to Total Distributions Declared to Common Stock Reconciliation Federal Income Tax Note [Table Text Block] Subsequent Event Type [Domain] Subsequent Event Type [Domain] O 2026 M4 Dividends O 2026 M4 Dividends [Member] O 2026 M4 Dividends Forfeited (in dollars per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value Equity Offering Costs Stockholders' Equity, Policy [Policy Text Block] Investment Company [Abstract] Erroneously Awarded Compensation Recovery Erroneously Awarded Compensation Recovery [Table] Schedule of Fair Value Measurement Inputs and Valuation Techniques Fair Value Measurement Inputs and Valuation Techniques [Table Text Block] Interest Revenue Recognition, Interest [Policy Text Block] Main Street Capital Corporation 2022 Non-Employee Director Restricted Stock Plan Main Street Capital Corporation 2022 Non-Employee Director Restricted Stock Plan [Member] Main Street Capital Corporation 2022 Non-Employee Director Restricted Stock Plan Payment-in-kind interest Payment-in-Kind Interest Payment-in-Kind Interest Entity Current Reporting Status Net cash provided by (used in) financing activities Cash Provided by (Used in) Financing Activity, Including Discontinued Operation Control investments: Investment, Affiliated Issuer, Controlled [Member] Total Shareholder Return Amount Total Shareholder Return Amount Elgin AcquireCo, LLC Elgin AcquireCo, LLC [Member] Elgin AcquireCo, LLC Purchase of vested stock for employee payroll tax withholding Share-Based Payment Arrangement, Decrease for Tax Withholding Obligation Beverages Beverages [Member] Beverages Dividend payable as of period end and paid in the following period Investment Company, Tax Basis, Dividends Paid Or Payable Investment Company, Tax Basis, Dividends Paid Or Payable Total return based on change in NAV Investment Company, Total Return Line of Credit Facility [Line Items] Line of Credit Facility [Line Items] Main Street Capital Corporation 2022 Equity and Incentive Plan Main Street Capital Corporation 2022 Equity and Incentive Plan [Member] Main Street Capital Corporation 2022 Equity and Incentive Plan Total deferred tax expense Investment Income, Operating, Deferred Tax Expense (Benefit) Investment Income, Operating, Deferred Tax Expense (Benefit) CASH FLOWS FROM FINANCING ACTIVITIES Cash Provided by (Used in) Financing Activity, Including Discontinued Operation [Abstract] Units (as a percent) Investment Owned, Balance, Percent Of Shares Investment Owned, Balance, Percent Of Shares Market comparable / Enterprise value Valuation, Market And Enterprise Value Approach [Member] Valuation, Market And Enterprise Value Approach Hornblower Sub, LLC Hornblower Sub, LLC [Member] Hornblower Sub, LLC Line of credit facility, unused capacity, commitment fee (as a percent) Line of Credit Facility, Unused Capacity, Commitment Fee Percentage Financial Instruments [Domain] Financial Instruments [Domain] Variable Rate Component [Axis] Variable Rate Component [Axis] Variable Rate Component Expenses allocated to the External Investment Manager Expenses allocated Investment Company, Expense Offset Arrangement Underlying Securities Award Underlying Securities Amount Richardson Sales Solutions Richardson Sales Solutions [Member] Richardson Sales Solutions MVI MSO, LLC MVI MSO, LLC [Member] MVI MSO, LLC Public offering of common stock, net of offering costs Stock Issued During Period, Value, New Issues Average EBITDA Investment Company, Average Earnings Before Interest, Taxes, Depreciation, And Amortization Investment Company, Average Earnings Before Interest, Taxes, Depreciation, And Amortization Schedule of Financial Highlights Investment Company, Financial Highlights [Table Text Block] Debt instrument, remaining term (in years) Debt Instrument, Remaining Term Debt Instrument, Remaining Term Taxable income earned prior to period end and carried forward for distribution next period Investment Company, Tax Basis, Taxable Income Earned Prior To Period End and Carried Forward For Distribution Next Period Investment Company, Tax Basis, Taxable Income Earned Prior To Period End and Carried Forward For Distribution Next Period Computers & Peripherals Computers & Peripherals [Member] Computers & Peripherals Interface Security Systems, L.L.C Interface Security Systems, L.L.C [Member] Interface Security Systems, L.L.C O 2026 M5 Dividends O 2026 M5 Dividends [Member] O 2026 M5 Dividends Administrative services fees Administrative Service [Member] Garyline, LLC Garyline, LLC [Member] Garyline, LLC Restricted stock available for issuance (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Available for Grant Schedule of Related Party Transactions, by Related Party [Table] Related Party Transaction [Table] UserZoom Technologies, Inc. UserZoom Technologies, Inc. [Member] UserZoom Technologies, Inc. Harris Preston Fund Investments Harris Preston Fund Investments [Member] Harris Preston Fund Investments Commitments and Contingencies Disclosure [Abstract] All Trading Arrangements All Trading Arrangements [Member] Other Performance Measure, Amount Other Performance Measure, Amount Award Timing MNPI Considered Award Timing MNPI Considered [Flag] Current Fiscal Year End Date Consultation period subsequent to initial investment (in months) Investment Company, Consultation Period Subsequent To Initial Investment Investment Company, Consultation Period Subsequent To Initial Investment Units (in shares) Investment Owned, Balance, Shares LMM portfolio investments Lower Middle Market Portfolio [Member] Lower Middle Market Portfolio Non-PEO NEO Average Total Compensation Amount Non-PEO NEO Average Total Compensation Amount RA Outdoors LLC RA Outdoors LLC [Member] RA Outdoors LLC Interest and dividend receivable and other assets Interest And Dividend Receivable And Other Assets Interest And Dividend Receivable And Other Assets Change in Fair Value as of Vesting Date of Prior Year Equity Awards Vested in Covered Year Change in Fair Value as of Vesting Date of Prior Year Equity Awards Vested in Covered Year [Member] Common stock, dividend, per share, declared (in dollars per share) Common Stock, Dividends, Per Share, Declared Securities Act File Number Recovery of Erroneously Awarded Compensation Disclosure [Line Items] O 2026 M6 Dividends O 2026 M6 Dividends [Member] O 2026 M6 Dividends Measure: Measure [Axis] Advisory Agreement, Active Advisory Agreement, Active [Member] Advisory Agreement, Active Aggregate intrinsic value Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Nonvested Coregistics Buyer LLC Coregistics Buyer LLC [Member] Coregistics Buyer LLC Equity Components [Axis] Equity Components [Axis] Related Party Related Party [Member] Houston Plating and Coatings, LLC Houston Plating and Coatings, LLC [Member] Houston Plating and Coatings, LLC B-O-F Corporation B-O-F Corporation [Member] B-O-F Corporation Entity Interactive Data Current Variable Rate [Axis] Variable Rate [Axis] Percentage of total investment income, attributable to noncash paid-in-kind interest income (as a percent) Investment Company, Percentage Of Total Investment Income, Attributable To Noncash Paid-in-Kind Interest Income Investment Company, Percentage Of Total Investment Income, Attributable To Noncash Paid-in-Kind Interest Income Variable Rate Component Two Variable Rate Component Two [Member] Variable Rate Component Two Entity Small Business Purchase of vested stock for employee payroll tax withholding (in shares) Shares withheld for payroll taxes paid (in shares) Share-Based Payment Arrangement, Shares Withheld for Tax Withholding Obligation Adjustments to reconcile net increase in net assets resulting from operations to net cash provided by (used in) operating activities: Adjustments To Reconcile Net Assets From Operations To Cash Provided by (Used in) Operating Activities [Abstract] Adjustments To Reconcile Net Assets From Operations To Cash Provided by (Used in) Operating Activities Oil, Gas & Consumable Fuels Oil, Gas & Consumable Fuels [Member] Oil, Gas & Consumable Fuels MNPI Disclosure Timed for Compensation Value MNPI Disclosure Timed for Compensation Value [Flag] Horwitz Holdings, LLC Horwitz Holdings, LLC [Member] Horwitz Holdings, LLC Document Type Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fee multiple Measurement Input, Fee Multiple [Member] Measurement Input, Fee Multiple NET ASSET VALUE PER SHARE (in dollars per share) NAV as of the beginning of the period (in dollars per share) NAV as of the end of the period (in dollars per share) SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Significant Accounting Policies [Text Block] PIK Rate Investment, Interest Rate, Paid in Kind Colonial Electric Company LLC Colonial Electric Company LLC [Member] Colonial Electric Company LLC Inspire Aesthetics Management, LLC Inspire Aesthetics Management, LLC [Member] Inspire Aesthetics Management, LLC Subsequent Event [Line Items] Subsequent Event [Line Items] Statement of Stockholders' Equity [Abstract] Local Phone Number Canada CANADA Royal Cup Inc. Royal Cup Inc. [Member] Royal Cup Inc. Invincible Boat Company, LLC. Invincible Boat Company, LLC. [Member] Invincible Boat Company, LLC. TEC Services, LLC TEC Services, LLC [Member] TEC Services, LLC Schedule of Outstanding Commitments Investment Company, Outstanding Capital Commitments [Table Text Block] Investment Company, Outstanding Capital Commitments Electro Technical Industries, LLC Electro Technical Industries, LLC [Member] Electro Technical Industries, LLC Total deferred tax expense (benefit) Realized Gain (Loss), Investment And Derivative, Operating, Deferred Tax Expense (Benefit) Realized Gain (Loss), Investment And Derivative, Operating, Deferred Tax Expense (Benefit) Net unrealized appreciation (depreciation) (in dollars per share) Investment Company, Unrealized Gain (Loss) on Investment, Per Share Integral Energy Services Integral Energy Services [Member] Integral Energy Services Net income before taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Commitments and contingencies (Note K) Commitments and Contingencies O 2026 Q2 Regular Dividends O 2026 Q2 Regular Dividends [Member] O 2026 Q2 Regular Dividends Changed Peer Group, Footnote Changed Peer Group, Footnote [Text Block] Executive Category: Executive Category [Axis] CRC Evans USA Bidco, Inc. CRC Evans USA Bidco, Inc. [Member] CRC Evans USA Bidco, Inc. Debt issuance costs, net Proceeds From Debt Issuance Premiums, Net Proceeds From Debt Issuance Premiums, Net Per Share Data: Investment Company, Per Share Data [Abstract] Investment Company, Per Share Data Counterparty Name [Axis] Counterparty Name [Axis] PavCon LLC PavCon LLC [Member] PavCon LLC LIABILITIES and NET ASSETS Liabilities and Equity [Abstract] July 2026 Notes July 2026 Notes [Member] July 2026 Notes Other Commitments [Table] Other Commitments [Table] Unfunded commitments Accounts Payable, Other Investment Management Agreement Investment Management Agreement [Member] Investment Management Agreement Non-PEO NEO Average Compensation Actually Paid Amount Non-PEO NEO Average Compensation Actually Paid Amount Increase in common stock, dividends, per share, declared, monthly (as a percent) Increase (Decrease) In Common Stock, Dividends, Declared, Monthly Increase (Decrease) In Common Stock, Dividends, Declared, Monthly UnionRock Energy Fund Investments UnionRock Energy Fund Investments [Member] UnionRock Energy Fund Investments Supplemental cash flow disclosures: Supplemental Cash Flow Information [Abstract] PEO Name PEO Name DMA Industries, LLC DMA Industries, LLC [Member] DMA Industries, LLC Achieved total return on investments (as a percent) Investment Company, Achieved Total Return Investment Company, Achieved Total Return Taxes paid Income Tax Paid, before Refund Received Unearned Income—Debt Origination Fees and Original Issue Discount and Discounts / Premiums to Par Value Unearned Income [Policy Text Block] Unearned Income Stock Price or TSR Estimation Method Stock Price or TSR Estimation Method [Text Block] Entity Tax Identification Number Prepaids and other assets Prepaid Expense and Other Assets Other Commitments [Line Items] Other Commitments [Line Items] O 2026 A2 Regular Dividends O 2026 A2 Regular Dividends [Member] O 2026 A2 Regular Dividends Sale of stock, shares authorized under agreement (in shares) Sale Of Stock, Shares Authorized Under Agreement Sale Of Stock, Shares Authorized Under Agreement Entity Incorporation, State or Country Code Book-tax difference from share-based compensation expense Investment Company, Tax Basis, Book-tax Difference From Share-based Compensation Expense, Increase (Decrease) In Taxable Income Investment Company, Tax Basis, Book-tax Difference From Share-based Compensation Expense, Increase (Decrease) In Taxable Income Percentage of total investment income, attributable to interest income, debt investments, net (as a percent) Investment Company, Percentage Of Total Investment Income, Attributable To Interest Income, Debt Investments, Net Investment Company, Percentage Of Total Investment Income, Attributable To Interest Income, Debt Investments, Net MS Private Loan Fund II, LP MS Private Loan Fund II, LP [Member] MS Private Loan Fund II, LP Aggregate Erroneous Compensation Not Yet Determined Aggregate Erroneous Compensation Not Yet Determined [Text Block] Management and service fees, incentive rate (as a percent) Management and Service Fees, Incentive Rate BLI Acquisition, LLC BLI Acquisition, LLC [Member] BLI Acquisition, LLC Brightwood Capital Fund Investments Brightwood Capital Fund Investments Brightwood Capital Fund Investments [Member] Brightwood Capital Fund Investments Material Terms of Trading Arrangement Material Terms of Trading Arrangement [Text Block] Vesting Date Fair Value of Equity Awards Granted and Vested in Covered Year Vesting Date Fair Value of Equity Awards Granted and Vested in Covered Year [Member] ORGANIZATION AND BASIS OF PRESENTATION Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Measurement Frequency [Domain] Measurement Frequency [Domain] Debt Instrument [Axis] Subsequent Event [Table] Subsequent Event [Table] Share-based compensation expense Share-Based Payment Arrangement, Noncash Expense Salaries, share-based compensation and other personnel costs Labor and Related Expense Deferred compensation (in shares) Related Party Transaction, Transaction Amount, Shares Related Party Transaction, Transaction Amount, Shares Amounts of transaction Related Party Transaction, Amounts of Transaction Harris Preston Fund Investments Harris Preston Fund Investments One [Member] Harris Preston Fund Investments One Measurement Input Type [Axis] Measurement Input Type [Axis] Insider Trading Arrangements [Line Items] Pre-tax book income not consolidated for tax purposes Investment Company, Tax Basis, Pre-tax Book (Income) Loss Not Consolidated For Tax purposes, Increase (Decrease) In Taxable Income Investment Company, Tax Basis, Pre-tax Book (Income) Loss Not Consolidated For Tax purposes, Increase (Decrease) In Taxable Income Analytical Systems Keco Holdings, LLC Analytical Systems Keco Holdings, LLC [Member] Analytical Systems Keco Holdings, LLC December 2025 Series B Notes December 2025 Series B Notes [Member] December 2025 Series B Notes Deferred fees and other Increase (Decrease) In Deferred Fees and Other Increase (Decrease) In Deferred Fees and Other Behavior Development Group Holdings Behavior Development Group Holdings [Member] Behavior Development Group Holdings Aggregate Change in Present Value of Accumulated Benefit for All Pension Plans Reported in Summary Compensation Table Aggregate Change in Present Value of Accumulated Benefit for All Pension Plans Reported in Summary Compensation Table [Member] Private Loan Fund I Private Loan Fund I [Member] Private Loan Fund I Committed capital Investment Company, Financial Support to Investee Contractually Required, Not Provided, Amount Net assets, percentage (as a percent) Investments in and Advances to Affiliates, Percentage Of Net Assets Investments in and Advances to Affiliates, Percentage Of Net Assets Compensation Actually Paid vs. Company Selected Measure Compensation Actually Paid vs. Company Selected Measure [Text Block] Ratio of total expenses, including income tax expense, to average NAV Investment Company, Expense Ratio, Including Income Tax Expense Investment Company, Expense Ratio, Including Income Tax Expense Fair Value Measurement Inputs and Valuation Techniques [Table] Fair Value Measurement Inputs and Valuation Techniques [Table] PPL RVs, Inc. PPL RVs, Inc. [Member] PPL RVs, Inc. Concentration risk (as a percent) Concentration Risk, Percentage Auto Components Auto Components [Member] Auto Components Equity Awards Adjustments Equity Awards Adjustments [Member] Core Transformers Core Transformers [Member] Core Transformers Buca C, LLC Buca C, LLC [Member] Buca C, LLC Industry Sector [Domain] Industry Sector [Domain] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Volusion, LLC Volusion, LLC [Member] Volusion, LLC Plan Name [Axis] Plan Name [Axis] Investment owned, percent of net assets (as a percent) Investment Owned, Net Assets, Percentage Margin Effective Period [Domain] Margin Effective Period [Domain] Margin Effective Period [Domain] Short-term portfolio investments Short-Term Investments [Member] Forfeited (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Forfeited in Period General and administrative General and administrative General and Administrative Expense Share purchase program, percentage of outstanding stock maximum (as a percent) Share Purchase Program, Percentage of Outstanding Stock Maximum Share Purchase Program, Percentage of Outstanding Stock Maximum Dividends paid (in dollars per share) Investment Company, Distribution to Shareholders, Per Share Weighted-average annual effective yield (as a percent) Debt Securities, Available-for-Sale, Weighted Average Yield Statement of Cash Flows [Abstract] Midwest US Midwest Region [Member] Aggregate Available Trading Arrangement, Securities Aggregate Available Amount Portfolio Investment Classification and Valuation of the Investment Portfolio Investment, Policy [Policy Text Block] Accounts payable to MSCC and its subsidiaries Accounts Payable Diversified Consumer Services Diversified Consumer Services [Member] Diversified Consumer Services ArborWorks, LLC ArborWorks, LLC [Member] ArborWorks, LLC Cody Pools, Inc. Cody Pools, Inc. [Member] Cody Pools, Inc. Pay vs Performance Disclosure Pay vs Performance Disclosure [Table] Investment Company, Financial Highlights [Table] Investment Company, Financial Highlights [Table] Entity Filer Category Director Director [Member] Dividends [Axis] Dividends [Axis] Weighted-average effective interest rate Average interest rate (as a percent) Debt Instrument, Interest Rate During Period Concentration Risk Benchmark [Domain] Concentration Risk Benchmark [Domain] NET INVESTMENT INCOME Net Investment Income [Abstract] Gamber-Johnson Holdings, LLC Gamber-Johnson Holdings, LLC [Member] Gamber-Johnson Holdings, LLC Net change in unrealized appreciation (depreciation) on assets still held Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss) DIVIDEND REINVESTMENT PLAN Stockholders' Equity, Dividend Reinvestment Plan [Text Block] Stockholders' Equity, Dividend Reinvestment Plan Deferred tax expense (benefit): Investment Tax Expense (Income), Deferred [Abstract] Investment Tax Expense (Income), Deferred NET INCREASE IN NET ASSETS RESULTING FROM OPERATIONS PER SHARE—BASIC (in dollars per share) Investment Company, Investment Income (Loss) from Operations, Per Share, Per Basic Share Investment Company, Investment Income (Loss) from Operations, Per Share, Per Basic Share Entity Address, Address Line Two March 2029 Notes March 2029 Notes [Member] March 2029 Notes Total investment income Total investment income Gross Investment Income, Operating Food Products Food Products [Member] Food Products Industry Concentration Risk Industry Concentration Risk [Member] Industry Concentration Risk Entity Address, Address Line One Vested (in dollars per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value Winter Services LLC Winter Services LLC [Member] Winter Services LLC Tax expense Income Tax Expense (Benefit) Investments in and Advances to Affiliates, at Fair Value [Roll Forward] Investments in and Advances to Affiliates, at Fair Value [Roll Forward] Other Other [Member] Other Total distributions accrued or paid to common stockholders Investment Company, Tax Basis, Distributions Accrued Or Paid To Common Stockholders Investment Company, Tax Basis, Distributions Accrued Or Paid To Common Stockholders Principles of Consolidation Consolidation, Policy [Policy Text Block] Portfolio turnover ratio Investment Company, Portfolio Turnover Escalent, Inc. Escalent, Inc. [Member] Escalent, Inc. MSC III Main Street Capital III, LP [Member] Main Street Capital III, LP Discounted cash flow Valuation Technique, Discounted Cash Flow [Member] Statement [Table] Statement [Table] Total current tax expense (benefit) Realized Gain (Loss), Investment And Derivative, Operating, Tax Expense (Benefit), Current Realized Gain (Loss), Investment And Derivative, Operating, Tax Expense (Benefit), Current O 2025 Q2 Supplemental Dividends O 2025 Q2 Supplemental Dividends [Member] O 2025 Q2 Supplemental Dividends Investment Type Concentration Risk Investment Type Concentration Risk [Member] Investment Type Concentration Risk Total current tax expense Investment Income, Operating, Tax Expense (Benefit), Current Investment Income, Operating, Tax Expense (Benefit), Current Interest income Interest income Investment Income, Interest Professional Services Professional Services [Member] Professional Services Chamberlin Holding LLC Chamberlin Holding LLC [Member] Chamberlin Holding LLC American Nuts, LLC American Nuts, LLC [Member] American Nuts, LLC Cash and Cash Equivalents [Axis] Cash and Cash Equivalents [Axis] Mission Critical Group Mission Critical Group [Member] Mission Critical Group