Geographic concentration Geographic Concentration Risk [Member] Functional Translations Foreign Currency Transactions and Translations Policy [Policy Text Block] Related Party Transactions [Abstract] Summary of Changes in Net Assets Investment Company, Changes in Net Assets [Table Text Block] Entity Address, Postal Zip Code Entity Address, Postal Zip Code Variable Rate Component [Domain] Variable Rate Component [Domain] Variable Rate Component [Domain] PIK income Interest Income, Operating, Paid in Kind Unfunded commitments, fair value Investment Company, Financial Commitment to Investee, Future Amount, Fair Value Investment Company, Financial Commitment to Investee, Future Amount, Fair Value Construction & Building Construction Sector [Member] Number of financial institutions Number Of Financial Institutions Number Of Financial Institutions Preferred stock, outstanding (in shares) Preferred stock at beginning of period (in shares) Preferred stock at end of period (in shares) Preferred Stock, Shares Outstanding Discounted Cash Flow Valuation Technique, Discounted Cash Flow [Member] High Tech Industries Technology Sector [Member] Debt Instrument [Axis] Debt Instrument [Axis] Maximum borrowing capacity Total Facility Line of Credit Facility, Maximum Borrowing Capacity Related party expense Related Party Transaction, Expenses from Transactions with Related Party Income Tax Disclosure [Abstract] Class A-1 Notes Credit Fund II Senior Notes, Class A-1 Notes [Member] Credit Fund II Senior Notes, Class A-1 Notes Interest, PIK Investment, Interest Rate, Paid in Kind Investment Company, Net Assets [Roll Forward] Investment Company, Net Assets [Roll Forward] 2019 Notes 2019 Senior Unsecured Notes [Member] 2019 Senior Unsecured Notes Solaero Technology Corp. Solaero Technology Corp. [Member] Solaero Technology Corp. Consumer Services Consumer Services [Member] Consumer Services Net change in unrealized appreciation (depreciation) Debt and Equity Securities, Unrealized Gain (Loss) [Member] Debt and Equity Securities, Unrealized Gain (Loss) Investment Company, Nonconsolidated Subsidiary [Axis] Investment Company, Nonconsolidated Subsidiary [Axis] Base management fees (Note 4) Base management fees Management Fee Expense Paid-in capital in excess of par value Additional Paid in Capital Independent Directors' Services Independent Directors' Services [Member] Independent Directors' Services Income Approach Valuation, Income Approach [Member] Fair Value Measurement [Domain] Fair Value Measurement [Domain] Financial Instruments [Domain] Financial Instruments [Domain] Basis spread on variable rate Debt Instrument, Basis Spread on Variable Rate Base management and incentive fees payable Increase (Decrease) in Management and Incentive Fees Payable Credit Fund Warehouse II Facility Credit Fund Warehouse II Facility [Member] Credit Fund Warehouse II Facility Statistical Measurement [Domain] Statistical Measurement [Domain] Interest rate Investment Interest Rate Interest expense Interest Expense, Debt, Excluding Amortization Credit Fund Facility Credit Fund Facility [Member] Credit Fund Facility Quarterly catch-up rate Investment Advisory Agreement - Incentive Rate, Quarterly Catch-Up Threshold [Member] Investment Advisory Agreement - Incentive Rate, Quarterly Catch-Up Threshold Stated interest rate Debt Instrument, Interest Rate, Stated Percentage Valuation Approach and Technique [Axis] Valuation Approach and Technique [Axis] LITIGATION Legal Matters and Contingencies [Text Block] Credit Facility The Credit Facility [Member] The Credit Facility 2020 Notes 2020 Senior Unsecured Notes [Member] 2020 Senior Unsecured Notes Accumulated Net Realized Gain (Loss) Investment Company, Distributable Earnings, Accumulated Net Realized Gain (Loss) [Member] Investment Company, Distributable Earnings, Accumulated Net Realized Gain (Loss) Consumer Goods: Non-Durable Consumer Goods, Non-Durable [Member] Consumer Goods, Non-Durable Investment, Issuer Name [Domain] Investment, Issuer Name [Domain] Financial Support for Nonconsolidated Legal Entity [Table] Financial Support for Nonconsolidated Legal Entity [Table] Stock repurchase program, cumulative value of shares repurchased Stock Repurchase Program, Cumulative Value Of Shares Repurchased Stock Repurchase Program, Cumulative Value Of Shares Repurchased Preferred stock dividend Dividends, Preferred Stock Taxes, including excise tax, paid during the period Income Taxes Paid Dividend payable (Note 10) Dividends Payable Net increase (decrease) in net assets resulting from operations Net increase (decrease) in net assets resulting from operations Net Income (Loss) Attributable to Parent Measurement Input Type [Domain] Measurement Input Type [Domain] Debt securities Debt Securities [Member] Subsequent Event Type [Axis] Subsequent Event Type [Axis] Dividend income Dividend Income, Operating Net investment income (loss) before taxes Net Investment Income Supplemental common dividend declared Supplemental Dividend Declared [Member] Supplemental Dividend Declared Equity Component [Domain] Equity Component [Domain] Subsequent Event Type [Domain] Subsequent Event Type [Domain] Scenario [Axis] Scenario [Axis] Discount Rate Measurement Input, Discount Rate [Member] Secured debt Secured Debt [Member] Financial Support for Nonconsolidated Legal Entity [Line Items] Financial Support for Nonconsolidated Legal Entity [Line Items] Ownership [Axis] Ownership [Axis] Dividend and Interest Income Interest and Dividend Income, Securities, Operating Investment, Name [Domain] Investment, Name [Domain] Principal proceeds available for reinvestment Debt Instrument, Principal Proceeds Available For Reinvestment Debt Instrument, Principal Proceeds Available For Reinvestment Valuation Approach and Technique [Domain] Valuation Approach and Technique [Domain] Nominal value decrease Investment Owned, Face Amount, Increase (Decrease) Investment Owned, Face Amount, Increase (Decrease) Related Party [Domain] Related Party [Domain] 2015-1 Notes, Class A-1B Notes 2015-1 Notes, Class A-1B Notes [Member] 2015-1 Notes, Class A-1B Notes Net investment income (loss) (in dollars per share) Investment Company, Investment Income (Loss), Per Share Containers, Packaging & Glass Container and Packaging Sector [Member] Directors’ fees and expenses Noninterest Expense Directors Fees Average amount per portfolio company Investment Owned, Average Principal Amount Per Portfolio Company Investment Owned, Average Principal Amount Per Portfolio Company Supplemental disclosures: Supplemental Cash Flow Information [Abstract] Interest income Interest Income, Operating, Paid in Cash Statement of Cash Flows [Abstract] Secured borrowings (Note 7) Secured borrowings Outstanding Borrowing, beginning of period Outstanding Borrowing, end of period Borrowings Outstanding Long-Term Line of Credit Entity Address, State or Province Entity Address, State or Province Level 1 Fair Value, Inputs, Level 1 [Member] Consensus Pricing Valuation Technique, Consensus Pricing Model [Member] Investment Company, Nonconsolidated Subsidiary [Table] Investment Company, Nonconsolidated Subsidiary [Table] Sales Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales Receivable for investment sold/repaid Receivable, Investment, Sale 1-3 years Contractual Obligation, to be Paid, Year Two and Three Interest, spread Investment, Basis Spread, Variable Rate Telecommunications Telecommunications Sector [Member] Telecommunications Sector SIGNIFICANT ACCOUNTING POLICIES Basis of Presentation and Significant Accounting Policies [Text Block] Net cash provided by (used in) operating activities Net Cash Provided by (Used in) Operating Activities Related Party Transaction [Domain] Related Party Transaction [Domain] Unfunded delayed draw commitments Financial Support, Unfunded Delayed Draw Commitments [Member] Financial Support, Unfunded Delayed Draw Commitments Swingline loan Bridge Loan [Member] Other liabilities Other Liabilities Excise tax expense Investment Income, Operating, Tax Expense (Benefit) Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table] Dividends declared (in dollars per share) Investment Company, Distribution to Shareholders, Per Share Legal Entity [Axis] Legal Entity [Axis] Weighted average interest rate Line of Credit Facility, Interest Rate During Period Debt and equity securities Securities (Assets) [Member] CONSOLIDATED FINANCIAL HIGHLIGHTS Investment Company, Financial Highlights [Text Block] Automotive Automotive Sector [Member] Total liabilities Liabilities Preferred stock, conversion price (in dollars per share) Preferred Stock, Convertible, Conversion Price Geographical [Axis] Geographical [Axis] Industry Sector [Domain] Industry Sector [Domain] Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Mezzanine Loan Investment Fund, Mezzanine Loan [Member] Investment Fund, Mezzanine Loan Investment, Identifier [Axis] Investment, Identifier [Axis] Administration Agreement Administration Agreement [Member] Administration Agreement Preferred stock, issued (in shares) Preferred Stock, Shares Issued Document Type Document Type Concentration Risk Benchmark [Domain] Concentration Risk Benchmark [Domain] Schedule of Consolidated Financial Highlights Investment Company, Financial Highlights [Table Text Block] BORROWINGS NOTES PAYABLE Debt Disclosure [Text Block] Entity Shell Company Entity Shell Company Ratios/Supplemental Data: Investment Company, Supplemental Data [Abstract] Investment Company, Supplemental Data Selected Consolidated Balance Sheet Information Investment Company, Selected Consolidated Balance Sheet Information [Abstract] Investment Company, Selected Consolidated Balance Sheet Information Changes in operating assets: Increase (Decrease) in Operating Assets [Abstract] Line of Credit Facility, Increase (Decrease) [Roll Forward] Line of Credit Facility, Increase (Decrease) [Roll Forward] Line of Credit Facility, Increase (Decrease) Financial Instrument [Axis] Financial Instrument [Axis] Average principal debt outstanding Line of Credit Facility, Average Outstanding Amount Net gain (loss) included in earnings Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings Affiliated entity Affiliated Entity [Member] Subsequent event Subsequent Event [Member] Document Period End Date Document Period End Date Weighted-average common shares outstanding Weighted Average Number of Shares Outstanding, Basic And Diluted [Abstract] Weighted Average Number of Shares Outstanding, Basic And Diluted 2019-2 Notes, Class C Notes 2019-2 Notes, Class C Notes [Member] 2019-2 Notes, Class C Notes Gain (loss) on sale of investments Gain (Loss) on Sale of Investments Investment type concentration Investment Type Concentration Risk [Member] Investment Type Concentration Risk 2015-1 Notes, Class A-2 Notes 2015-1 Notes, Class A-2 Notes [Member] 2015-1 Notes, Class A-2 Notes Investment, measurement input Investment Owned, Fair Value, Measurement Input Investment Owned, Fair Value, Measurement Input Total assets Assets Debt Disclosure [Abstract] Basic and diluted earnings per share Earnings Per Share [Abstract] Proceeds from sales and repayments of investments and change in receivable for investments sold/repaid Proceeds from Disposition of Investment, Operating Activity Income Statement Location [Axis] Income Statement Location [Axis] 90-day SOFR 90-Day SOFR [Member] 90-Day SOFR Quarterly common dividend declared Dividend Declared [Member] Summary of Investment Holdings [Line Items] Summary of Investment Holdings [Line Items] Reference rate Investment, Reference Rate Investment, Reference Rate Subordinated loans and members’ equity Members' Equity Investment, Issuer Affiliation [Domain] Investment, Issuer Affiliation [Domain] Preferred stock, liquidation preference (in dollars per share) Preferred Stock, Liquidation Preference Per Share Net cash provided by (used in) financing activities Net Cash Provided by (Used in) Financing Activities Ratio to average net assets attributable to Common Stockholders: Investment Company, Financial Ratios [Abstract] Implied discount rate Investment, Implied Discount Rate Investment, Implied Discount Rate Long-term debt Long-Term Debt, Fair Value Accounting Policies [Abstract] Stock repurchase program, authorized amount Stock Repurchase Program, Authorized Amount Interest expense, debt Total interest expense and credit facility fees Interest Expense, Debt Pre-incentive fee net investment income, exceeds catch-up threshold Investment Advisory Agreement - Incentive Rate, Pre-Incentive Fee Net Investment Income Exceeds Catch-Up Threshold [Member] Investment Advisory Agreement - Incentive Rate, Pre-Incentive Fee Net Investment Income Exceeds Catch-Up Threshold Line of credit Line of Credit [Member] EQUITY Stockholders' Equity Attributable to Parent [Abstract] Interest and dividend receivable Dividend and Interest Receivable Preferred stock, dividends declared (in dollars per share) Preferred Stock, Dividends Per Share, Declared Schedule of Investments [Line Items] Schedule of Investments [Line Items] Cash, Cash Equivalents and Restricted Cash Cash and Cash Equivalents, Policy [Policy Text Block] Related Party Transaction [Line Items] Related Party Transaction [Line Items] 2019-2 Notes, Class A-1 Notes 2019-2 Notes, Class A-1 Notes [Member] 2019-2 Notes, Class A-1 Notes 2015-1R Notes payable, net of unamortized debt issuance costs Other Notes Payable Par/principal amount Senior secured loans Investment Owned, Balance, Principal Amount Leisure Products & Services Leisure Products & Services Sector [Member] Leisure Products & Services Sector Administrative service fees payable (Note 4) Administrative Service Fee Payable Administrative Service Fee Payable Entity Registrant Name Entity Registrant Name Investments in and Advances to Affiliates, at Fair Value [Roll Forward] Investments in and Advances to Affiliates, at Fair Value [Roll Forward] SUBSEQUENT EVENTS Subsequent Events [Text Block] Floating Rate Floating Rate [Member] Floating Rate Preferred stock, dividend rate, cash Preferred Stock, Dividend Rate, Percentage, Cash Preferred Stock, Dividend Rate, Percentage, Cash Cyprus CYPRUS Entity Address, City or Town Entity Address, City or Town Benchmark rate Benchmark Rate [Member] Benchmark Rate Middle Market Credit Funds Middle Market Credit Fund LLC And Middle Market Credit Fund II LLC [Member] Middle Market Credit Fund LLC And Middle Market Credit Fund II LLC Expenses: Operating Expenses [Abstract] Offering Costs Offering Costs, Common Stock And Other Securities [Member] Offering Costs, Common Stock And Other Securities MIDDLE MARKET CREDIT FUND, LLC MIDDLE MARKET CREDIT FUND II, LLC Investments in and Advances to Affiliates, Schedule of Investments [Text Block] Industry Sector [Axis] Industry Sector [Axis] Asset Class [Domain] Asset Class [Domain] Summary of Investment Holdings [Table] Summary of Investment Holdings [Table] Minimum Low Minimum [Member] Net realized gain (loss) and net change in unrealized appreciation (depreciation): Net Realized Gains (Losses) And Investment Owned, Recognized Unrealized Appreciation (Depreciation), Net [Abstract] Net Realized Gains (Losses) And Investment Owned, Recognized Unrealized Appreciation (Depreciation), Net Statement of Financial Position [Abstract] Entity Emerging Growth Company Entity Emerging Growth Company Common stock, par value (in dollars per share) Common Stock, Par or Stated Value Per Share Commitments and Contingencies Disclosure [Abstract] Deferred financing costs Debt Issuance Costs, Net Fixed Rate Fixed Rate [Member] Fixed Rate FAIR VALUE MEASUREMENTS Fair Value Disclosures [Text Block] 90-day LIBOR 90-Day LIBOR [Member] 90-Day LIBOR Investment, Name [Axis] Investment, Name [Axis] Additions/Purchases Investments in and Advances to Affiliates, at Fair Value, Gross Additions Trading Symbol Trading Symbol Entity File Number Securities Act File Number Net realized gains (losses) Debt and Equity Securities, Realized Gain (Loss) [Member] Debt and Equity Securities, Realized Gain (Loss) Diversified Financial Services Diversified Financial Services [Member] Diversified Financial Services Second Lien Debt Debt Securities, Second Lien [Member] Debt Securities, Second Lien Aaa/AAA Class A-1-1-R Notes 2015-1 Notes, Class A-1-1-R [Member] 2015-1 Notes, Class A-1-1-R Summarized Financial Information Investment Company, Nonconsolidated Subsidiary, Summarized Financial Information [Table Text Block] Canada CANADA Net asset value Fair Value Measured at Net Asset Value Per Share [Member] Administrative service fees (Note 4) Administrative Fees Expense Restricted cash and cash equivalents Restricted Cash and Cash Equivalents Thereafter Variable Rate Component, After Two Years [Member] Variable Rate Component, After Two Years Schedule of Credit Facilities Schedule of Line of Credit Facilities [Table Text Block] Borrowings Proceeds from Lines of Credit Concentration Risk Benchmark [Axis] Concentration Risk Benchmark [Axis] Use of Estimates Use of Estimates, Policy [Policy Text Block] First 24 months Variable Rate Component, First Two Years [Member] Variable Rate Component, First Two Years LIBOR London Interbank Offered Rate (LIBOR) [Member] Investment Advisory Agreement Investment Advisory Agreement [Member] Investment Advisory Agreement Interest and credit facility fees payable (Notes 7 and 8) Interest and credit facilities payable Interest and credit facility fees payable Interest Payable And Line Of Credit Facility, Commitment Fee Payable Interest Payable And Line Of Credit Facility, Commitment Fee Payable Subsequent Events [Abstract] Concentration risk percentage Concentration Risk, Percentage Proceeds from contribution of investments Proceeds From Contribution Of Investment, Operating Activity Proceeds From Contribution Of Investment, Operating Activity 3-5 years Contractual Obligation, to be Paid, Year Four and Five TAX Income Tax Disclosure [Text Block] Weighted average interest rate Debt, Weighted Average Interest Rate Due to related party Due to Related Parties Tax return of capital Investment Company, Tax Return of Capital Distribution Credit Facility [Domain] Credit Facility [Domain] Metals & Mining Metals And Mining [Member] Metals And Mining Changes in operating liabilities: Increase (Decrease) in Operating Liabilities [Abstract] Interest paid during the period Interest Paid, Excluding Capitalized Interest, Operating Activities Basic (in dollars per share) Earnings Per Share, Basic Investments in and Advances to Affiliates [Table] Investments in and Advances to Affiliates [Table] Net increase (decrease) in net assets resulting from operations: Net Income (Loss), Including Portion Attributable to Noncontrolling Interest [Abstract] SOFR Secured Overnight Financing Rate (SOFR) [Member] Secured Overnight Financing Rate (SOFR) Reductions/Sales/ Paydowns Investments in and Advances to Affiliates, at Fair Value, Gross Reductions Concentration Risk Type [Domain] Concentration Risk Type [Domain] Counterparty Name [Domain] Counterparty Name [Domain] Total net assets Net Assets at beginning of period Net Assets at end of period Stockholders' Equity Attributable to Parent Independent directors Director [Member] Percent of net assets Investment Owned, Percent of Net Assets Total Investments [Member] Line of Credit Facility [Line Items] Line of Credit Facility [Line Items] 30-day SOFR 30-Day SOFR [Member] 30-Day SOFR Ownership [Domain] Ownership [Domain] Aerospace & Defense Aerospace Sector [Member] Entity Interactive Data Current Entity Interactive Data Current Sale of stock, number of shares issued Sale of Stock, Number of Shares Issued in Transaction Interest and credit facility fees payable Increase (Decrease) In Interest Payable And Line Of Credit Facility, Commitment Fee Payable Increase (Decrease) In Interest Payable And Line Of Credit Facility, Commitment Fee Payable Market price per common share, end of period (in dollars per share) Investment Company, Market Value Per Share Other (in dollars per share) Investment Company, Other, Per Share Investment Company, Other, Per Share Pre-incentive fee net investment income, below catch-up threshold Investment Advisory Agreement - Incentive Rate, Pre-Incentive Fee Net Investment Income Below Catch-Up Threshold [Member] Investment Advisory Agreement - Incentive Rate, Pre-Incentive Fee Net Investment Income Below Catch-Up Threshold Portion at Fair Value Measurement Portion at Fair Value Measurement [Member] Dividends paid in cash Payments of Dividends BBB- Class C Notes 2015-1 Notes, BBB- Class C Notes [Member] 2015-1 Notes, BBB- Class C Notes Capital transactions: Investment Company, Capital Share Transactions [Abstract]   Common Stock Common Stock [Member] Weighted average yields of senior secured loans based on amortized cost Investment Owned, At Cost, Yield Investment Owned, At Cost, Yield Retail Retail Sector [Member] Repurchase of common stock Payments for Repurchase of Common Stock Controlled/affiliated Investment, Affiliated Issuer, Controlled [Member] Portfolio turnover Investment Company, Portfolio Turnover Income Taxes Income Tax, Policy [Policy Text Block] Revenue Recognition Revenue [Policy Text Block] Adjustments to reconcile net increase (decrease) 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 Statement [Table] Statement [Table] Stock repurchase program, average cost (in dollars per share) Stock Repurchase Program, Average Cost Per Share Stock Repurchase Program, Average Cost Per Share Document Quarterly Report Document Quarterly Report Investment Company, Changes in Net Assets [Line Items] Investment Company, Changes in Net Assets [Line Items] Letter of credit Letter of Credit [Member] Schedule of Fair Value Inputs and Valuation Techniques Fair Value Measurement Inputs and Valuation Techniques [Table Text Block] Statistical Measurement [Axis] Statistical Measurement [Axis] Business Services Business Services [Member] Business Services Level 1, 2 and 3 Fair Value, Inputs, Level 1, Level 2, and Level 3 [Member] Total return based on market price Investment Company, Total Return, Market Value Related Party Transaction [Axis] Related Party Transaction [Axis] Component one Variable Rate Component, Component One [Member] Variable Rate Component, Component One Total distributable earnings (loss) Retained Earnings (Accumulated Deficit) Interest expense and credit facility fees Investment Company, Interest Expense Ratio, Including Line Of Credit Facility, Commitment Fee Investment Company, Interest Expense Ratio, Including Line of Credit Facility Commitment Fee Interest rate floor Investment, Interest Rate, Floor Equity Components [Axis] Equity Components [Axis] Scenario [Domain] Scenario [Domain] Dividends declared on preferred and common stock (Note 10) Ordinary income Investment Company, Dividend Distribution Net change in unrealized appreciation (depreciation) included in earnings related to investments still held at the reporting date included in net change in unrealized appreciation (depreciation) on investments on the Consolidated Statements of Operations Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss) Committed capital (up to) Investment Company, Committed Capital Dividends Payable [Table] Dividends Payable [Table] RELATED PARTY TRANSACTIONS Related Party Transactions Disclosure [Text Block] Schedule of Investments [Abstract] Investment Company, Nonconsolidated Subsidiary [Domain] Investment Company, Nonconsolidated Subsidiary [Domain] Document Fiscal Year Focus Document Fiscal Year Focus Variable Rate Component [Axis] Variable Rate Component [Axis] Variable Rate Component United Kingdom UNITED KINGDOM Cash flows from operating activities: Net Cash Provided by (Used in) Operating Activities [Abstract] Statement [Line Items] Statement [Line Items] Class A-2 Notes Credit Fund II Senior Notes, Class A-2 Notes [Member] Credit Fund II Senior Notes, Class A-2 Notes Fair Value Measurement Inputs and Valuation Techniques [Table] Fair Value Measurement Inputs and Valuation Techniques [Table] Payable for investments purchased Payable, Investment, Purchase 2019-2 Notes, Class B Notes 2019-2 Notes, Class B Notes [Member] 2019-2 Notes, Class B Notes Net change in unrealized appreciation (depreciation) on investments Net change in unrealized (appreciation) depreciation on investments Net Change in Unrealized Appreciation (Depreciation) Debt and Equity Securities, Unrealized Gain (Loss) Investments, at fair value Fair value Fair value, beginning balance Fair value, ending balance Investment Owned, at Fair Value Variable Rate [Domain] Variable Rate [Domain] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Investment, Issuer Name [Axis] Investment, Issuer Name [Axis] Second Lien Debt Second Lien Debt [Member] Second Lien Debt Repurchase of common stock Stock Repurchased During Period, Value Document Transition Report Document Transition Report State Street Sub-Administration Agreement State Street Sub-Administration Agreement [Member] State Street Sub-Administration Agreement Local Phone Number Local Phone Number Number of tranches Debt Instrument, Number Of Tranches Debt Instrument, Number Of Tranches Collateral amount, cash Cash Collateral for Borrowed Securities Recent Accounting Standards Updates New Accounting Pronouncements, Policy [Policy Text Block] Amount Available Line of Credit Facility, Current Borrowing Capacity Prepaid expenses and other assets Increase (Decrease) in Prepaid Expense and Other Assets Common stock, outstanding (in shares) Common stock at beginning of period (in shares) Common stock at end of period (in shares) Number of common shares outstanding, end of period Common Stock, Shares, Outstanding Industry concentration Industry Concentration Risk [Member] Industry Concentration Risk Investment purchase price, percent of aggregate outstanding balance, minimum Investment Owned, Purchase Price, Percent Of Aggregate Outstanding Balance, Minimum Investment Owned, Purchase Price, Percent Of Aggregate Outstanding Balance, Minimum Total base management fees and incentive fees Management Fee And Incentive Fee Expense Management Fee And Incentive Fee Expense Investment, Issuer Affiliation [Axis] Investment, Issuer Affiliation [Axis] Geographical [Domain] Geographical [Domain] NYFRB rate Federal Reserve Bank of New York [Member] Federal Reserve Bank of New York Preferred stock, par value (in dollars per share) Preferred Stock, Par or Stated Value Per Share Income Statement [Abstract] Foreign currency translation Line of Credit Facility, Increase (Decrease), Foreign Currency Translation Adjustment Line of Credit Facility, Increase (Decrease), Foreign Currency Translation Adjustment Capital in Excess of Par Value Additional Paid-in Capital [Member] Net realized gain (loss) Realized Gain (Loss), Investment, Derivative, and Foreign Currency Transaction Price Change, Operating, after Tax Document Fiscal Period Focus Document Fiscal Period Focus Net increase (decrease) in net assets resulting from operations attributable to Common Stockholders Net Income (Loss) Available to Common Stockholders [Abstract] Net Income (Loss) Available to Common Stockholders Diluted (in shares) Weighted Average Number of Shares Outstanding, Diluted Other general and administrative Other General and Administrative Expense Common stock Common Stock, Value, Issued Carrying Value Reported Value Measurement [Member] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Preferred Stock Preferred Stock [Member] Senior notes Senior Notes [Member] Federal funds effective rate Federal Funds Effective Rate [Member] Federal Funds Effective Rate Less than one year Contractual Obligation, to be Paid, Remainder of Fiscal Year Other income Other Income Preferred stock, authorized (in shares) Preferred Stock, Shares Authorized Private placement Private Placement [Member] Credit Fund II Middle Market Credit Fund II, LLC [Member] Middle Market Credit Fund II, LLC Luxembourg LUXEMBOURG Cash, cash equivalents and restricted cash Cash, cash equivalents, and restricted cash, beginning of period Cash, cash equivalents, and restricted cash, end of period Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents Adjusted SOFR rate Adjusted Secured Overnight Financing Rate (SOFR) [Member] Adjusted Secured Overnight Financing Rate (SOFR) Investment balance (shares) Investment Owned, Balance, Shares COMMMITMENTS AND CONTINGENCIES Commitments and Contingencies Disclosure [Text Block] Dividend receivable Increase (Decrease) in Dividends Receivable Net increase (decrease) in net assets resulting from operations attributable to Common Stockholders Basic Net Income (Loss) Available to Common Stockholders, Basic Sovereign & Public Finance Sovereign And Public Finance [Member] Sovereign And Public Finance Common stock, issued (in shares) Common Stock, Shares, Issued Aaa/AAA Class A-1-2-R Notes 2015-1 Notes, Class A-1-2-R [Member] 2015-1 Notes, Class A-1-2-R Net increase (decrease) in net assets resulting from capital share transactions Investment Company, Capital Transactions, Increase (Decrease) Investment Company, Capital Transactions, Increase (Decrease) 2015-1 Notes, Class A-1C Notes 2015-1 Notes, Class A-1C Notes [Member] 2015-1 Notes, Class A-1C Notes 180-day LIBOR 180-Day LIBOR [Member] 180-Day LIBOR Income Statement Location [Domain] Income Statement Location [Domain] 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] Amendment Flag Amendment Flag Basis spread on variable rate Derivative, Basis Spread on Variable Rate Professional fees Professional Fees Face amount Debt Instrument, Face Amount Investment Type [Axis] Investment Type [Axis] Indicative Quotes Measurement Input, Quoted Price [Member] Investments Investment, Policy [Policy Text Block] Borrowings on SPV Credit Facility and Credit Facility Proceeds from Long-Term Lines of Credit Italy ITALY Weighted average yields of senior secured loans based on fair value Investment Owned, At Fair Value, Yield Investment Owned, At Fair Value, Yield Entity Current Reporting Status Entity Current Reporting Status Preferred stock dividend Preferred Stock Dividends, Income Statement Impact Market Approach Valuation, Market Approach [Member] Total return based on net asset value Investment Company, Total Return Net increase (decrease) in net assets resulting from operations (in dollars per share) Investment Company, Investment Income (Loss) from Operations, Per Share Unused capacity commitment fee Line of Credit Facility, Unused Capacity, Commitment Fee Percentage 2015-1 Notes, Class A-1A Notes 2015-1 Notes, Class A-1A Notes [Member] 2015-1 Notes, Class A-1A Notes Alternate base rate Alternate Base Rate [Member] Alternate Base Rate Chemicals, Plastics & Rubber Chemicals, Plastics And Rubber [Member] Chemicals, Plastics And Rubber Credit Fund Middle Market Credit Fund, LLC [Member] Middle Market Credit Fund, LLC Selected Consolidated Statement of Operations Information: Investment Company, Consolidated Statement of Operations Information [Abstract] Investment Company, Consolidated Statement of Operations Information Counterparty Name [Axis] Counterparty Name [Axis] Schedule of Related Party Transactions Schedule of Related Party Transactions [Table Text Block] Investment Company, Nonconsolidated Subsidiary [Line Items] Investment Company, Nonconsolidated Subsidiary [Line Items] IPO IPO [Member] Non-controlled/affiliated Investment, Affiliated Issuer, Noncontrolled [Member] Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Cost of investments purchased and change in payable for investments purchased Payments for Purchase of Investment, Operating Activity AA Class A-2-R Notes 2015-1 Notes, Class A-2-R [Member] 2015-1 Notes, Class A-2-R Basis of Presentation Basis of Accounting, Policy [Policy Text Block] LIABILITIES Liabilities [Abstract] Summary of Dividends Declared Dividends Declared [Table Text Block] Dividends declared on preferred stock and common stock during the period Dividends declared Dividends Sale of stock, offering price (in dollars per share) Sale of Stock, Price Per Share Net realized and unrealized gain (loss) on investments and non-investment assets and liabilities Realized and Unrealized Gain (Loss), Investment, Derivative, and Foreign Currency Transaction, Operating, after Tax Common stock, authorized (in shares) Common Stock, Shares Authorized Schedule of Related Party Transactions, by Related Party [Table] Schedule of Related Party Transactions, by Related Party [Table] Termination notice, number of written days notice threshold Related Party, Termination Notice, Number Of Written Days Notice Threshold Related Party, Termination Notice, Number Of Written Days Notice Threshold Investment Funds Transactions Investment Funds Transactions [Member] Investment Funds Transactions Maximum High Maximum [Member] Accretion due to share repurchases (in dollars per share) Investment Company, Repurchase of Shares, Per Share Net change in unrealized appreciation (depreciation) on investments: Investment Owned, Recognized Unrealized Appreciation (Depreciation), Net [Abstract] Net Unrealized Gains (Losses) Interest and credit facility expenses Total interest expense and credit facility fees Interest and Debt Expense Repurchase of common stock Repurchase of common stock Stock Repurchased and Retired During Period, Value Wholesale Wholesale Sector [Member] Wholesale Sector Dividends Payable [Line Items] Dividends Payable [Line Items] Entity Small Business Entity Small Business Measurement Basis [Axis] Measurement Basis [Axis] Unfunded revolving loan commitments Financial Support, Unfunded Revolving Loan Commitments [Member] Financial Support, Unfunded Revolving Loan Commitments NET ASSETS Stockholders' Equity Note Disclosure [Text Block] Common dividend declared (in dollars per share) Common Stock, Dividends, Per Share, Declared 2019-2 Notes, Class A-2 Notes 2019-2 Notes, Class A-2 Notes [Member] 2019-2 Notes, Class A-2 Notes Investment income: Revenues [Abstract] Senior Notes, net of unamortized debt issuance costs Senior Notes Dividends and Distributions to Common Stockholders Stockholders' Equity, Policy [Policy Text Block] Line of Credit Facility [Table] Line of Credit Facility [Table] Restricted cash Restricted Cash Schedule of Investments Measured at Fair Value on Recurring Basis Fair Value, Assets Measured on Recurring Basis [Table Text Block] Currency gains (losses) on non-investment assets and liabilities Net realized currency (gain) loss on non-investment assets and liabilities Foreign Currency Transaction Gain (Loss), Realized Interest rate type concentration Interest Rate Type Concentration Risk [Member] Interest Rate Type Concentration Risk Schedule of Carrying Values and Fair Values of Debt Schedule of Carrying Values and Estimated Fair Values of Debt Instruments [Table Text Block] Investment owned, nominal value Investment Owned, Face Amount Summary of Payment Obligations Contractual Obligation, Fiscal Year Maturity [Table Text Block] Net realized gain (loss) and net change in unrealized appreciation (depreciation) on investments and non-investment assets and liabilities (in dollars per share) Investment Company, Gain (Loss) on Investment, Per Share Number of loans on non-accrual status Investment Owned, Non-Accrual Status, Number Of Loans Investment Owned, Non-Accrual Status, Number Of Loans Repurchase of common stock (in shares) Repurchase of common stock (in shares) Stock Repurchased and Retired During Period, Shares Subordinated Subordinated Debt [Member] Schedule of estimated tax character of dividends declared Schedule Of Estimated Tax Character Of Dividends Declared [Table Text Block] Schedule Of Estimated Tax Character Of Dividends Declared PIK income Capitalized Interest, Operating, Paid In Kind Capitalized Interest, Operating, Paid In Kind Recovery Rate Measurement Input, Recovery Rate [Member] Measurement Input, Recovery Rate Title of 12(b) Security Title of 12(b) Security Credit Fund Sub Facility Credit Fund Sub Facility [Member] Credit Fund Sub Facility Comparable Multiple Measurement Input, Comparable Multiple [Member] Measurement Input, Comparable Multiple Agreement period Related Party Transaction, Term Related Party Transaction, Term Percentage of portfolio at fixed interest rates Investment Owned, Percent At Fixed Interest Rates Investment Owned, Percent At Fixed Interest Rates Accretion due to share repurchases (in dollars per share) Stock Repurchase Program, Accretion Of Net Assets Per Share Stock Repurchase Program, Accretion Of Net Assets Per Share Subsequent Event [Line Items] Subsequent Event [Line Items] Investment Funds Investment Funds [Member] Investment Funds 2015-1 Issuer Preferred Interests 2015-1 Issuer Preferred Interests [Member] 2015-1 Issuer Preferred Interests Repayments Repayments of Lines of Credit Component two Variable Rate Component, Component Two [Member] Variable Rate Component, Component Two Debt Instrument [Line Items] Debt Instrument [Line Items] Restricted investments, fair value Restricted Investments, at Fair Value Interest expense payable Interest Payable Other accrued expenses and liabilities Other Accrued Liabilities Number of loans Investment Company, Number of Loans Investment Company, Number of Loans Fair Value Measurement Inputs and Valuation Techniques [Line Items] Fair Value Measurement Inputs and Valuation Techniques [Line Items] Debt issuance costs paid Payments of Debt Issuance Costs Net accretion of discount on investments Accretion (Amortization) of Discounts and Premiums, Investments Other accrued expenses and liabilities Increase (Decrease) in Other Accrued Liabilities Healthcare & Pharmaceuticals Healthcare Sector [Member] 2019-2 Notes 2019-2 Notes [Member] 2019-2 Notes Net increase (decrease) in net assets Stockholders' Equity, Period Increase (Decrease) LIABILITIES AND MEMBERS’ EQUITY Liabilities and Equity [Abstract] Fair Value Estimate of Fair Value Measurement [Member] Unfunded commitments, principal amount Total unfunded commitments Investment Company, Financial Commitment to Investee, Future Amount Fair Value, Recurring and Nonrecurring [Table] Fair Value, Recurring and Nonrecurring [Table] Energy: Oil & Gas Energy Sector, Oil And Gas [Member] Energy Sector, Oil And Gas Unused commitment fees payable Credit Facility Fees Payable, Unused Commitment Fees Credit Facility Fees Payable, Unused Commitment Fees 30-day LIBOR 30-Day LIBOR [Member] 30-Day LIBOR Other expenses Other Expenses Sale of stock, consideration received Sale of Stock, Consideration Received on Transaction Software Software Sector [Member] Software Sector Incentive rate Management and Service Fees, Incentive Rate ORGANIZATION Nature of Operations [Text Block] Number of investments sold Number Of Investments Sold Number Of Investments Sold Entity Filer Category Entity Filer Category Basic (in shares) Weighted-average shares outstanding (in shares) Weighted Average Number of Shares Outstanding, Basic Preferred stock, dividend rate, stock Preferred Stock, Dividend Rate, Percentage, Stock Preferred Stock, Dividend Rate, Percentage, Stock Collateral amount, debt instrument Debt Instrument, Collateral Amount Financial Support to Nonconsolidated Legal Entity [Domain] Financial Support to Nonconsolidated Legal Entity [Domain] United States UNITED STATES Investments at fair value Investments, At Fair Value [Member] Investments, At Fair Value Expenses before incentive fees Investment Company, Expense Ratio Excluding Incentive Fee Capital Equipment Capital Equipment [Member] Capital Equipment Annualized hurdle rate Investment Advisory Agreement - Incentive Rate, Annualized Hurdle Rate [Member] Investment Advisory Agreement - Incentive Rate, Annualized Hurdle Rate Commitments and contingencies (Notes 9 and 12) Commitments and Contingencies Schedule of Investments Investment Holdings, Schedule of Investments [Table Text Block] Security Exchange Name Security Exchange Name More than 5 years Contractual Obligation, to be Paid, after Year Five Net change in unrealized appreciation (depreciation) on investments Unrealized Gain (Loss), Investment and Derivative, Operating, after Tax Maximum borrowing capacity, accordion feature option Line of Credit Facility, Accordion Feature, Higher Borrowing Capacity Option Line of Credit Facility, Accordion Feature, Higher Borrowing Capacity Option Credit Partners Credit Partners USA LLC [Member] Credit Partners USA LLC Net assets attributable to Common Stockholders, end of period Net Assets Cumulative convertible preferred stock Preferred Stock, Value, Issued Capital contribution Financial Support, Capital Contributions [Member] Accumulated Net Investment Income (Loss) Investment Company, Distributable Earnings, Accumulated Net Investment Income (Loss) [Member] Investment Company, Distributable Earnings, Accumulated Net Investment Income (Loss) Components of Interest Expense Schedule of Debt [Table Text Block] Financial Support to Nonconsolidated Legal Entity [Axis] Financial Support to Nonconsolidated Legal Entity [Axis] Schedule of Level 3 Input Reconciliation Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block] First Lien Debt Debt Securities, First Lien [Member] Debt Securities, First Lien Prepaid expenses and other assets Prepaid Expense and Other Assets Dividends [Domain] Dividends [Domain] Cover [Abstract] Schedule of Long-Term Debt Instruments [Table] Schedule of Long-Term Debt Instruments [Table] Level 3 Fair Value, Inputs, Level 3 [Member] Per Common Share Data: Investment Company, Financial Highlights [Roll Forward] Other assets Other Assets Base management and incentive fees payable (Note 4) Base management and incentive fees payable Management Fee Payable And Incentive Fee Payable Management Fee Payable And Incentive Fee Payable Investment Funds Other than Securities Investment [Member] Realized capital gains incentive fees Investment Advisory Agreement - Incentive Rate, Realized Capital Gains [Member] Investment Advisory Agreement - Incentive Rate, Realized Capital Gains Investments [Domain] Investments [Domain] Forecast Forecast [Member] Total Contractual Obligation Media: Diversified & Production Media, Diversified And Production [Member] Media, Diversified And Production Base management fee rate Management and Service Fees, Base Rate Sweden SWEDEN Rate Type [Domain] Rate Type [Domain] Rate Type [Domain] Liabilities and members’ equity Liabilities and Equity CCLF Cliffwater Corporate Lending Fund [Member] Cliffwater Corporate Lending Fund Net change in unrealized currency gains (losses) on non-investment assets and liabilities Net change in unrealized currency (gains) losses on non-investment assets and liabilities Foreign Currency Transaction Gain (Loss), Unrealized 2019-2 Issuer Preferred Interests 2019-2 Issuer Preferred Interests [Member] 2019-2 Issuer Preferred Interests Amortization of deferred financing costs Amortization of Debt Issuance Costs Related Party [Axis] Related Party [Axis] Long-Term Debt, Type [Axis] Long-Term Debt, Type [Axis] Repayments of SPV Credit Facility and Credit Facility Repayments of Long-Term Lines of Credit Annualized catch-up rate Investment Advisory Agreement - Incentive Rate, Annualized Catch-Up Threshold [Member] Investment Advisory Agreement - Incentive Rate, Annualized Catch-Up Threshold Paydowns Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements Ownership interest Limited Liability Company (LLC) or Limited Partnership (LP), Managing Member or General Partner, Ownership Interest Organization, Consolidation and Presentation of Financial Statements [Abstract] Non-controlled/non-affiliated Investment, Unaffiliated Issuer [Member] Level 2 Fair Value, Inputs, Level 2 [Member] The Credit Facility, Senior Notes, and 2015-1R Notes – Related Costs, Expenses and Deferred Financing Costs Debt, Policy [Policy Text Block] Media: Advertising, Printing & Publishing Media, Advertising, Printing And Publishing [Member] Media, Advertising, Printing And Publishing Restricted investments, percent of net assets Restricted Investments, Percent of Net Assets Offering costs Offering Costs, Common Stock And Other Securities Offering Costs, Common Stock And Other Securities Current Fiscal Year End Date Current Fiscal Year End Date Purchases Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases Diluted Net Income (Loss) Available to Common Stockholders, Diluted Fair value of loans on non-accrual status Investment Owned, Non-Accrual Status, At Fair Value Investment Owned, Non-Accrual Status, At Fair Value Diluted (in dollars per share) Earnings Per Share, Diluted Sale of Stock [Domain] Sale of Stock [Domain] Accretion of discount Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Accretion of Discount Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Accretion of Discount 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] Net realized gain (loss) on investments Net realized (gain) loss on investments Net Realized Gain (Loss) Debt and Equity Securities, Realized Gain (Loss) Concentration Risk Type [Axis] Concentration Risk Type [Axis] Asset coverage ratio Asset coverage, end of period Investment Company, Senior Security, Indebtedness, Asset Coverage Ratio Expected percent of net assets Investment Owned, Percent Of Net Assets, Expected Investment Owned, Percent Of Net Assets, Expected Credit Fund II Senior Notes Credit Fund II Senior Notes [Member] Credit Fund II Senior Notes Credit Partners and the company Credit Partners USA LLC And Carlyle Secured Lending, Inc [Member] Credit Partners USA LLC And Carlyle Secured Lending, Inc NET ASSETS PER COMMON SHARE (in dollars per share) Net asset value per common share, beginning of period (in dollars per share) Net asset value per common share, end of period (in dollars per share) Net Asset Value Per Share Equity Investments Equity Securities [Member] Preferred stock, dividend rate, annual increase Preferred Stock, Dividend Rate, Percentage, Annual Increase Preferred Stock, Dividend Rate, Percentage, Annual Increase Net investment income (loss) Investment Company, Investment Income (Loss) Ratio Total expenses Investment Income, Investment Expense Schedule of Unfunded Commitments Financial Support for Nonconsolidated Legal Entity [Table Text Block] Financial Support for Nonconsolidated Legal Entity Administrative service fees payable Increase (Decrease) In Administrative Service Fee Payable Increase (Decrease) In Administrative Service Fee Payable Entity Address, Address Line Two Entity Address, Address Line Two Entity Address, Address Line One Entity Address, Address Line One Stock repurchase program, increase amount Stock Repurchase Program, Additional Authorized Amount Stock Repurchase Program, Additional Authorized Amount Net change in unrealized appreciation (depreciation) on investments Unrealized Gain (Loss) on Investments Transportation: Cargo Transportation Sector [Member] Stated interest rate, maximum increase Debt Instrument, Interest Rate, Increase (Decrease), Maximum Debt Instrument, Interest Rate, Increase (Decrease), Maximum Fair Value Disclosures [Abstract] Unused  Portion Line of Credit Facility, Remaining Borrowing Capacity Environmental Industries Environmental Industries [Member] Environmental Industries Interest expense (Notes 7 and 8) Interest Expense Quarterly hurdle rate Investment Advisory Agreement - Incentive Rate, Quarterly Hurdle Rate [Member] Investment Advisory Agreement - Incentive Rate, Quarterly Hurdle Rate Collateral, number of loans Debt Instrument, Collateral, Number Of Loans Debt Instrument, Collateral, Number Of Loans Incentive fees (Note 4) Total incentive fees Incentive Fee Expense Credit Facility [Axis] Credit Facility [Axis] Unfunded commitments, unused fee Investment Company, Financial Commitment to Investee, Future Amount, Unused Fee Percentage Investment Company, Financial Commitment to Investee, Future Amount, Unused Fee Percentage Total investment income Total investment income Gross Investment Income, Operating Total capital gains incentive fees Investment Advisory Agreement - Incentive Rate, Total Capital Gains [Member] Investment Advisory Agreement - Incentive Rate, Total Capital Gains Equity [Abstract] Subsequent Event [Table] Subsequent Event [Table] Consumer Goods: Durable Consumer Goods, Durable [Member] Consumer Goods, Durable Investment Company [Abstract] Fair value of loans with PIK provisions Investment Owned, Paid In Kind, At Fair Value Investment Owned, Paid In Kind, At Fair Value Entity Tax Identification Number Entity Tax Identification Number Schedule of Investments [Table] Schedule of Investments [Table] Net investment income (loss) Net investment income (loss) Investment Income, Operating, after Expense and Tax Stock repurchase program, stock repurchased since inception (in shares) Stock Repurchase Program, Number Of Shares Repurchased Since Inception Stock Repurchase Program, Number Of Shares Repurchased Since Inception Percentage of portfolio at floating interest rates Investment Owned, Percent At Floating Interest Rates Investment Owned, Percent At Floating Interest Rates Investment Company, Changes in Net Assets [Table] Investment Company, Changes in Net Assets [Table] Net change in unrealized currency gains (losses) on non-investment assets and liabilities Foreign Currency Transaction Gain (Loss), Unrealized, after Tax Number of portfolio companies in Credit Fund Investment Owned, Number Of Portfolio Companies Investment Owned, Number Of Portfolio Companies Interest receivable Increase (Decrease) in Accrued Interest Receivable, Net Effective annualized weighted average interest rate Debt Instrument, Interest Rate During Period Investment owned, percentage received Investment Owned, Percentage Investment Owned, Percentage Net increase (decrease) in cash, cash equivalents and restricted cash Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect Rate Type [Axis] Rate Type [Axis] Rate Type Credit facility fees (Note 7) Facility unused commitment fee Line of Credit Facility, Commitment Fee Amount PIK loan Payment in Kind (PIK) Note [Member] Investments, amortized cost Amortized cost Investment Owned, at Cost Net realized gain (loss) on investments: Net Realized Gains (Losses) [Abstract] Net Realized Gains (Losses) Beverage & Food Food and Beverage Sector [Member] Entity Central Index Key Entity Central Index Key Credit spread Measurement Input, Credit Spread [Member] Subordinated Loan and Member's Interest Investment Funds, Subordinated Loan and Member's Interest [Member] Investment Funds, Subordinated Loan and Member's Interest Utilities: Electric Utilities Sector, Electric [Member] Utilities Sector, Electric Aaa/AAA Class A-1-3-R Notes 2015-1 Notes, Class A-1-3-R [Member] 2015-1 Notes, Class A-1-3-R Measurement Input Type [Axis] Measurement Input Type [Axis] Entity [Domain] Entity [Domain] City Area Code City Area Code Financial support, cumulative amount Nonconsolidated Legal Entity, Financial Support Cumulative Amount Line of credit and senior notes Line Of Credit And Senior Notes [Member] Line Of Credit And Senior Notes ASSETS Assets [Abstract] Other credit facility fees payable Credit Facility Fees Payable, Other Credit Facility Fees Payable, Other Long-Term Debt, Type [Domain] Long-Term Debt, Type [Domain] Statement of Stockholders' Equity [Abstract] Sale of Stock [Axis] Sale of Stock [Axis] Balance, beginning of period Balance, end of period Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value 2015-1 Notes 2015-1 Notes [Member] 2015-1 Notes Dividends [Axis] Dividends [Axis] Cash flows from financing activities: Net Cash Provided by (Used in) Financing Activities [Abstract] Limited Liability Company Limited Liability Company [Member] Asset Class [Axis] Asset Class [Axis] Earnings Per Common Share Earnings Per Share, Policy [Policy Text Block] Variable Rate [Axis] Variable Rate [Axis] Accumulated Net Unrealized Appreciation (Depreciation) Investment Company, Distributable Earnings, Net Unrealized Appreciation (Depreciation) [Member] Investment Company, Distributable Earnings, Net Unrealized Appreciation (Depreciation) Incentive fees on pre-incentive fee net investment income Investment Advisory Agreement - Incentive Rate, Pre-Incentive Fee Net Investment Income [Member] Investment Advisory Agreement - Incentive Rate, Pre-Incentive Fee Net Investment Income Expenses after incentive fees Investment Company, Expense Ratio Including Incentive Fee Weighted Average Weighted Average [Member] A Class B Notes 2015-1 Notes, A Class B Notes [Member] 2015-1 Notes, A Class B Notes 2019-2 Notes, Class D Notes 2019-2 Notes, Class D Notes [Member] 2019-2 Notes, Class D Notes Schedule of Basic and Diluted Earnings Per Share Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Accrued capital gains incentive fees Investment Advisory Agreement - Incentive Rate, Accrued Capital Gains [Member] Investment Advisory Agreement - Incentive Rate, Accrued Capital Gains Default Rate Measurement Input, Default Rate [Member]