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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) $ in Millions | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
Sep. 30, 2025 USD ($) company | Sep. 30, 2024 company | Sep. 30, 2025 USD ($) segment | Sep. 30, 2024 | Sep. 30, 2025 USD ($) company | Jun. 30, 2025 company | Dec. 31, 2024 USD ($)
Schedule of Investments [Line Items] |  |  |  |  |  |  |
Concentration risk, percentage (as a percent) |  |  | 100.00% |  |  |  | 100.00%
Cash equivalents | $ | $ 12.3 |  | $ 12.3 |  | $ 12.3 |  | $ 14.4
Cash balances exceeded federal deposit insurance corporation insurance protection levels | $ | $ 4.8 |  | $ 4.8 |  | $ 4.8 |  | $ 13.5
Percentage of total investment income, attributable to noncash paid-in-kind interest income (as a percent) | 6.50% | 6.70% | 5.90% | 5.40% |  |  |
Percentage of total investment income, attributable to noncash cumulative dividend income (as a percent) | 0.90% | 0.10% | 0.90% | 0.10% |  |  |
Percentage of total investment income, attributable to interest income, debt investments, net (as a percent) | 2.40% | 3.00% | 2.40% | 2.80% |  |  |
Number of reportable segments | segment |  |  | 1 |  |  |  |
Investment Owned, At Fair Value | Investment Type Concentration Risk |  |  |  |  |  |  |
Schedule of Investments [Line Items] |  |  |  |  |  |  |
Concentration risk, percentage (as a percent) |  |  | 100.00% |  |  |  | 100.00%
Investment Owned, At Fair Value | Investment Type Concentration Risk | Nonperforming Financial Instruments |  |  |  |  |  |  |
Schedule of Investments [Line Items] |  |  |  |  |  |  |
Concentration risk, percentage (as a percent) |  |  | 1.40% |  |  |  | 1.50%
Investment Owned, At Cost | Investment Type Concentration Risk |  |  |  |  |  |  |
Schedule of Investments [Line Items] |  |  |  |  |  |  |
Concentration risk, percentage (as a percent) |  |  | 100.00% |  |  |  | 100.00%
Investment Owned, At Cost | Investment Type Concentration Risk | Nonperforming Financial Instruments |  |  |  |  |  |  |
Schedule of Investments [Line Items] |  |  |  |  |  |  |
Concentration risk, percentage (as a percent) |  |  | 4.60% |  |  |  | 5.60%
Private Loan portfolio investments |  |  |  |  |  |  |
Schedule of Investments [Line Items] |  |  |  |  |  |  |
Consultation period subsequent to initial investment |  |  | 12 months |  |  |  |
Investment company, number of portfolio companies with annual third-party appraisal was obtained, reviewed and certified | company | 14 | 17 |  |  |  | 61 |
Percentage of portfolio with annual third-party appraisal was obtained, reviewed and certified (as a percent) |  |  |  |  | 96.00% |  |
Private Loan portfolio investments | Investment Owned, At Fair Value | Investment Type Concentration Risk |  |  |  |  |  |  |
Schedule of Investments [Line Items] |  |  |  |  |  |  |
Concentration risk, percentage (as a percent) | 22.00% | 24.00% |  |  | 90.00% |  |
LMM portfolio investments |  |  |  |  |  |  |
Schedule of Investments [Line Items] |  |  |  |  |  |  |
Consultation period subsequent to initial investment |  |  | 12 months |  |  |  |
Investment company, number of portfolio companies with annual third-party appraisal was obtained, reviewed and certified | company | 12 | 12 |  |  | 50 |  |
Percentage of portfolio with annual third-party appraisal was obtained, reviewed and certified (as a percent) |  |  |  |  | 99.00% |  |
LMM portfolio investments | Investment Owned, At Fair Value | Investment Type Concentration Risk |  |  |  |  |  |  |
Schedule of Investments [Line Items] |  |  |  |  |  |  |
Concentration risk, percentage (as a percent) | 24.00% | 22.00% |  |  | 99.00% |  |
Middle Market portfolio investments |  |  |  |  |  |  |
Schedule of Investments [Line Items] |  |  |  |  |  |  |
Percentage of portfolio investments containing limited consultation with financial advisory services firm (as a percent) | 89.00% |  | 89.00% |  | 89.00% |  | 93.00%
Middle Market portfolio investments | Investment Owned, At Fair Value | Investment Type Concentration Risk |  |  |  |  |  |  |
Schedule of Investments [Line Items] |  |  |  |  |  |  |
Concentration risk, percentage (as a percent) |  |  | 2.10% |  |  |  | 3.30%
Middle Market portfolio investments | Investment Owned, At Cost | Investment Type Concentration Risk |  |  |  |  |  |  |
Schedule of Investments [Line Items] |  |  |  |  |  |  |
Concentration risk, percentage (as a percent) |  |  | 3.40% |  |  |  | 5.80%
Other Portfolio investments | Investment Owned, At Fair Value | Investment Type Concentration Risk |  |  |  |  |  |  |
Schedule of Investments [Line Items] |  |  |  |  |  |  |
Concentration risk, percentage (as a percent) |  |  | 1.30% |  |  |  | 2.00%
Other Portfolio investments | Investment Owned, At Cost | Investment Type Concentration Risk |  |  |  |  |  |  |
Schedule of Investments [Line Items] |  |  |  |  |  |  |
Concentration risk, percentage (as a percent) |  |  | 1.20% |  |  |  | 1.60%

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