Fair Value of Financial Instruments - Schedule of Fair Value Hierarchy of Cash and Investments (Details) - USD ($) $ in Thousands	Jun. 30, 2024		Dec. 31, 2023
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash	$ 331,201		$ 469,017
Total Investments at fair value	6,157,709	[1],[2],[3],[4]	6,132,022	[5],[6],[7],[8]
First-lien senior secured debt investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments at fair value	4,230,154		3,983,668
Second-lien senior secured debt investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments at fair value	342,402		454,090
Unsecured debt investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments at fair value	322,371		427,862
Preferred equity investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments at fair value	821,664		861,779
Common equity investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments at fair value	441,118		404,623
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash	331,201		469,017
Total Investments at fair value	46,434		75,928
Level 1 | First-lien senior secured debt investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments at fair value	0		0
Level 1 | Second-lien senior secured debt investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments at fair value	0		0
Level 1 | Unsecured debt investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments at fair value	0		0
Level 1 | Preferred equity investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments at fair value	0		0
Level 1 | Common equity investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments at fair value	46,434		75,928
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash	0		0
Total Investments at fair value	264,535		265,884
Level 2 | First-lien senior secured debt investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments at fair value	73,615		8,521
Level 2 | Second-lien senior secured debt investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments at fair value	172,892		218,798
Level 2 | Unsecured debt investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments at fair value	0		20,455
Level 2 | Preferred equity investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments at fair value	0		0
Level 2 | Common equity investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments at fair value	18,028		18,110
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash	0		0
Total Investments at fair value	5,846,740		5,790,210
Level 3 | First-lien senior secured debt investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments at fair value	4,156,539		3,975,147
Level 3 | Second-lien senior secured debt investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments at fair value	169,510		235,292
Level 3 | Unsecured debt investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments at fair value	322,371		407,407
Level 3 | Preferred equity investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments at fair value	821,664		861,779
Level 3 | Common equity investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments at fair value	$ 376,656		$ 310,585

[1] Certain portfolio company investments are subject to contractual restrictions on sales. Refer to footnote 19 for additional information on our restricted securities.

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

[3] Unless otherwise indicated, all investments are non-controlled, non-affiliated investments. Non-controlled, non-affiliated investments are defined as investments in which the Company owns less than 5% of the portfolio company’s outstanding voting securities and does not have the power to exercise control over the management or policies of such portfolio company.

[4] Unless otherwise indicated, the Company’s portfolio companies are pledged as collateral supporting the amounts outstanding under the Revolving Credit Facility, SPV Asset Facility I, SPV Asset Facility II and CLO 2020-1. See Note 5 “Debt”.

[5] Certain portfolio company investments are subject to contractual restrictions on sales. Refer to footnote 19 for additional information on our restricted securities.

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

[7] Unless otherwise indicated, all investments are non-controlled, non-affiliated investments. Non-controlled, non-affiliated investments are defined as investments in which the Company owns less than 5% of the portfolio company’s outstanding voting securities and does not have the power to exercise control over the management or policies of such portfolio company.

[8] Unless otherwise indicated, the Company’s portfolio companies are pledged as collateral supporting the amounts outstanding under the Revolving Credit Facility, SPV Asset Facility I, SPV Asset Facility II and CLO 2020-1. See Note 5 “Debt”.