Fair Value of Investments - Schedule of Quantitative Information About Significant Unobservable Inputs of Level 3 Investments (Details)	Sep. 30, 2023 USD ($)		Dec. 31, 2022 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 12,896,158,000	[1],[2],[3],[4]	$ 13,010,345,000	[5],[6],[7]
First-lien senior secured debt investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	8,875,037,000		9,279,179,000
Second-lien senior secured debt investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	1,783,604,000		1,860,978,000
Unsecured debt investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	276,071,000		248,019,000
Preferred equity investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	401,139,000		355,261,000
Common equity investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	1,190,595,000		977,927,000
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	12,414,731,000		12,666,277,000
Level 3 | First-lien senior secured debt investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	8,875,037,000		9,279,179,000
Level 3 | First-lien senior secured debt investments | Yield Analysis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	8,614,432,000		9,148,610,000
Level 3 | First-lien senior secured debt investments | Recent Transaction
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	200,596,000		86,606,000
Level 3 | First-lien senior secured debt investments | Collateral Analysis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	60,009,000		43,963,000
Level 3 | Second-lien senior secured debt investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	1,684,612,000		1,817,286,000
Level 3 | Second-lien senior secured debt investments | Yield Analysis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	1,676,175,000		1,806,340,000
Level 3 | Second-lien senior secured debt investments | Recent Transaction
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value			4,898,000
Level 3 | Second-lien senior secured debt investments | Collateral Analysis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	8,437,000		6,048,000
Level 3 | Unsecured debt investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	264,434,000		237,440,000
Level 3 | Unsecured debt investments | Yield Analysis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	258,662,000		232,280,000
Level 3 | Unsecured debt investments | Yield Analysis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	5,772,000		5,160,000
Level 3 | Preferred equity investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	401,139,000		355,261,000
Level 3 | Preferred equity investments | Yield Analysis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	401,139,000		339,821,000
Level 3 | Preferred equity investments | Recent Transaction
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value			15,395,000
Level 3 | Preferred equity investments | Yield Analysis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value			45,000
Level 3 | Common equity investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	1,189,509,000		977,111,000
Level 3 | Common equity investments | Yield Analysis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	9,416,000
Level 3 | Common equity investments | Recent Transaction | Transaction Price
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	188,172,000		99,210,000
Level 3 | Common equity investments | Yield Analysis | Transaction Price
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	4,533,000		4,215,000
Level 3 | Common equity investments | Yield Analysis | EBITDA Multiple
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	952,960,000		848,356,000
Level 3 | Common equity investments | Yield Analysis | Revenue
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	34,288,000		25,241,000
Level 3 | Common equity investments | Yield Analysis | Gross Profit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 140,000		$ 89,000
Level 3 | Minimum | First-lien senior secured debt investments | Yield Analysis | Market Yield
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)	0.089		0.082
Level 3 | Minimum | First-lien senior secured debt investments | Recent Transaction | Transaction Price
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)	0.970		0.975
Level 3 | Minimum | First-lien senior secured debt investments | Collateral Analysis | Recovery Rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)	0.855		0.510
Level 3 | Minimum | Second-lien senior secured debt investments | Yield Analysis | Market Yield
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)	0.121		0.126
Level 3 | Minimum | Second-lien senior secured debt investments | Recent Transaction | Transaction Price
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)			0.980
Level 3 | Minimum | Second-lien senior secured debt investments | Collateral Analysis | Recovery Rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)	0.133		0.095
Level 3 | Minimum | Unsecured debt investments | Yield Analysis | Market Yield
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)	0.117		0.104
Level 3 | Minimum | Unsecured debt investments | Yield Analysis | EBITDA Multiple
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)	12.4		14.3
Level 3 | Minimum | Preferred equity investments | Yield Analysis | Market Yield
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)	0.114		0.119
Level 3 | Minimum | Preferred equity investments | Recent Transaction | Transaction Price
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)			0.965
Level 3 | Minimum | Preferred equity investments | Yield Analysis | EBITDA Multiple
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)			11.5
Level 3 | Minimum | Common equity investments | Yield Analysis | Market Yield
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)	0.080
Level 3 | Minimum | Common equity investments | Recent Transaction | Transaction Price
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)	1.000		1
Level 3 | Minimum | Common equity investments | Yield Analysis | Transaction Price
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)	77.00		75.31
Level 3 | Minimum | Common equity investments | Yield Analysis | EBITDA Multiple
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)	1.2		1.2
Level 3 | Minimum | Common equity investments | Yield Analysis | Revenue
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)	1.9		0.8
Level 3 | Minimum | Common equity investments | Yield Analysis | Gross Profit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)	10.0		8.5
Level 3 | Maximum | First-lien senior secured debt investments | Yield Analysis | Market Yield
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)	0.273		0.420
Level 3 | Maximum | First-lien senior secured debt investments | Recent Transaction | Transaction Price
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)	1.000		0.990
Level 3 | Maximum | First-lien senior secured debt investments | Collateral Analysis | Recovery Rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)	0.855		0.510
Level 3 | Maximum | Second-lien senior secured debt investments | Yield Analysis | Market Yield
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)	0.298		0.210
Level 3 | Maximum | Second-lien senior secured debt investments | Recent Transaction | Transaction Price
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)			0.980
Level 3 | Maximum | Second-lien senior secured debt investments | Collateral Analysis | Recovery Rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)	0.133		0.095
Level 3 | Maximum | Unsecured debt investments | Yield Analysis | Market Yield
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)	0.180		0.202
Level 3 | Maximum | Unsecured debt investments | Yield Analysis | EBITDA Multiple
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)	12.4		14.3
Level 3 | Maximum | Preferred equity investments | Yield Analysis | Market Yield
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)	0.263		0.179
Level 3 | Maximum | Preferred equity investments | Recent Transaction | Transaction Price
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)			1.000
Level 3 | Maximum | Preferred equity investments | Yield Analysis | EBITDA Multiple
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)			11.5
Level 3 | Maximum | Common equity investments | Yield Analysis | Market Yield
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)	0.08
Level 3 | Maximum | Common equity investments | Recent Transaction | Transaction Price
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)	1.000		1
Level 3 | Maximum | Common equity investments | Yield Analysis | Transaction Price
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)	77.00		75.31
Level 3 | Maximum | Common equity investments | Yield Analysis | EBITDA Multiple
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)	19.3		23.3
Level 3 | Maximum | Common equity investments | Yield Analysis | Revenue
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)	14.3		16.6
Level 3 | Maximum | Common equity investments | Yield Analysis | Gross Profit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)	10.0		8.5
Level 3 | Weighted Average | First-lien senior secured debt investments | Yield Analysis | Market Yield
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)	0.134		0.131
Level 3 | Weighted Average | First-lien senior secured debt investments | Recent Transaction | Transaction Price
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)	0.989		0.978
Level 3 | Weighted Average | First-lien senior secured debt investments | Collateral Analysis | Recovery Rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)	0.855		0.510
Level 3 | Weighted Average | Second-lien senior secured debt investments | Yield Analysis | Market Yield
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)	0.162		0.160
Level 3 | Weighted Average | Second-lien senior secured debt investments | Recent Transaction | Transaction Price
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)			0.980
Level 3 | Weighted Average | Second-lien senior secured debt investments | Collateral Analysis | Recovery Rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)	0.133		0.095
Level 3 | Weighted Average | Unsecured debt investments | Yield Analysis | Market Yield
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)	0.132		0.124
Level 3 | Weighted Average | Unsecured debt investments | Yield Analysis | EBITDA Multiple
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)	12.4		14.3
Level 3 | Weighted Average | Preferred equity investments | Yield Analysis | Market Yield
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)	0.160		0.141
Level 3 | Weighted Average | Preferred equity investments | Recent Transaction | Transaction Price
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)			0.979
Level 3 | Weighted Average | Preferred equity investments | Yield Analysis | EBITDA Multiple
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)			11.5
Level 3 | Weighted Average | Common equity investments | Yield Analysis | Market Yield
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)	0.08
Level 3 | Weighted Average | Common equity investments | Recent Transaction | Transaction Price
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)	1.000		1
Level 3 | Weighted Average | Common equity investments | Yield Analysis | Transaction Price
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)	77.00		75.31
Level 3 | Weighted Average | Common equity investments | Yield Analysis | EBITDA Multiple
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)	4.6		5.5
Level 3 | Weighted Average | Common equity investments | Yield Analysis | Revenue
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)	10.3		12.2
Level 3 | Weighted Average | Common equity investments | Yield Analysis | Gross Profit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (Weighted Average)	10.0		8.5

[1] Certain portfolio company investments are subject to contractual restrictions on sales. Refer to footnote 28 for additional information on our restricted securities.

[2] Unless otherwise indicated, all investments are considered Level 3 investments.

[3] Unless otherwise indicated, loan contains a variable rate structure and may be subject to an interest rate floor. Variable rate loans bear interest at a rate that may be determined by reference to either the Secured Overnight Financing Rate ("SOFR" or "S," which can include one-, three- or six- month SOFR), London Interbank Offered Rate (“LIBOR” or “L”, which can include one-, three- or six- month LIBOR), Euro Interbank Offered Rate (“EURIBOR”), Great Britain Pound London Interbank Offered Rate (“GBPLIBOR” or “G”, which can include three- or six-month GBPLIBOR), SONIA ("SONIA” or "SA") or an alternate base rate (which can include the Federal Funds Effective Rate or the Prime Rate), at the borrower’s option, and which reset periodically based on the terms of the loan agreement.

[4] Unless otherwise indicated, the Company’s portfolio companies are pledged as collateral supporting the amounts outstanding under the Revolving Credit Facility, SPV Asset Facilities and CLOs. See Note 6 “Debt”.

[5] Certain portfolio company investments are subject to contractual restrictions on sales. Refer to footnote 28 for additional information on our restricted securities.

[6] Unless otherwise indicated, all investments are considered Level 3 investments.

[7] Unless otherwise indicated, the Company’s portfolio companies are pledged as collateral supporting the amounts outstanding under the Revolving Credit Facility, SPV Asset Facilities and CLOs. See Note 6 “Debt”.