FAIR VALUE MEASUREMENTS - Unobservable Inputs (Details)	Sep. 30, 2024 USD ($)	Dec. 31, 2023 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 5,698,660,000	$ 3,195,486,000	[1],[2]
Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	5,180,471,000	2,768,402,000
Level 3 | First Lien Debt | Yield Analysis | Discount Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 5,118,897,000	$ 2,710,858,000
Level 3 | First Lien Debt | Yield Analysis | Low | Discount Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.0768	0.0933
Level 3 | First Lien Debt | Yield Analysis | High | Discount Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.2785	0.2509
Level 3 | First Lien Debt | Yield Analysis | Weighted Average | Discount Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.0980	0.1099
Level 3 | Second Lien Debt | Yield Analysis | Discount Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 1,930,000	$ 21,708,000
Level 3 | Second Lien Debt | Yield Analysis | Low | Discount Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.0965	0.1335
Level 3 | Second Lien Debt | Yield Analysis | High | Discount Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.1395	0.3113
Level 3 | Second Lien Debt | Yield Analysis | Weighted Average | Discount Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.1219	0.1997
Level 3 | Other Debt Investments | Yield Analysis | Discount Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 6,062,000
Level 3 | Other Debt Investments | Yield Analysis | Low | Discount Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.0990
Level 3 | Other Debt Investments | Yield Analysis | High | Discount Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.1490
Level 3 | Other Debt Investments | Yield Analysis | Weighted Average | Discount Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.1240
Level 3 | Other Debt Investments | Income Approach | Discount Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value		$ 2,484,000
Level 3 | Other Debt Investments | Income Approach | Low | Discount Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input		0.1460
Level 3 | Other Debt Investments | Income Approach | High | Discount Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input		0.1460
Level 3 | Other Debt Investments | Income Approach | Weighted Average | Discount Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input		0.1460
Level 3 | Other Debt Investments | Market Approach | Discount Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 253,000
Level 3 | Other Debt Investments | Market Approach | Weighted Average | Discount Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	9
Level 3 | Preferred equity | Income Approach | Discount Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 40,769,000	$ 29,122,000
Level 3 | Preferred equity | Income Approach | Low | Discount Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.0988	0.1326
Level 3 | Preferred equity | Income Approach | High | Discount Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.1516	0.1568
Level 3 | Preferred equity | Income Approach | Weighted Average | Discount Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.1453	0.1504
Level 3 | Preferred equity | Market Approach | EBITDA Multiple
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 3,109,000
Level 3 | Preferred equity | Market Approach | Weighted Average | EBITDA Multiple
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	8.5
Level 3 | Common equity | Market Approach | Revenue Multiple
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 3,829,000	$ 2,604,000
Level 3 | Common equity | Market Approach | EBITDA Multiple
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 5,622,000	$ 1,626,000
Level 3 | Common equity | Market Approach | Low | Revenue Multiple
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	7.58	7.60
Level 3 | Common equity | Market Approach | Low | EBITDA Multiple
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	7.00	12.50
Level 3 | Common equity | Market Approach | High | Revenue Multiple
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	9.93	9.80
Level 3 | Common equity | Market Approach | High | EBITDA Multiple
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	18.70	18.70
Level 3 | Common equity | Market Approach | Weighted Average | Revenue Multiple
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	9.08	8.87
Level 3 | Common equity | Market Approach | Weighted Average | EBITDA Multiple
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	14.59	14.91

[1] Unless otherwise indicated, issuers of debt and equity investments held by the Company (which such term “Company” shall include the Company’s consolidated subsidiaries for purposes of this Consolidated Schedule of Investments) are denominated in dollars. All debt investments are income producing unless otherwise indicated. All equity investments are non-income producing unless otherwise noted. Certain portfolio company investments are subject to contractual restrictions on sales. Under the Investment Company Act of 1940, as amended (together with the rules and regulations promulgated thereunder, the “1940 Act”), the Company would be deemed to “control” a portfolio company if the Company owned more than 25% of its outstanding voting securities and/or held the power to exercise control over the management or policies of the portfolio company. As of December 31, 2023, the Company does not “control” any of these portfolio companies. Under the 1940 Act, the Company would be deemed an “affiliated person” of a portfolio company if the Company owns 5% or more of the portfolio company’s outstanding voting securities. As of December 31, 2023, the Company is not an “affiliated person” of any of its portfolio companies.

[2] Unless otherwise indicated, the Company's investments are pledged as collateral supporting the amounts outstanding under the ING Facility (as defined below). See Note 6 "Debt".