Investments - Investments at Fair Value and Amortized Cost (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Schedule of Investments [Line Items]
Amortized Cost	$ 12,823,971	$ 13,046,132	[1],[2],[3],[4],[5]
Fair Value	12,892,943	13,010,345	[2],[4],[5]
First-lien senior secured debt investments
Schedule of Investments [Line Items]
Amortized Cost	8,954,884	9,388,499
Fair Value	8,898,911	9,279,179
Second-lien senior secured debt investments
Schedule of Investments [Line Items]
Amortized Cost	1,889,071	1,934,274
Fair Value	1,822,865	1,860,978
Unsecured debt investments
Schedule of Investments [Line Items]
Amortized Cost	284,905	270,714
Fair Value	273,372	248,019
Preferred equity investments
Schedule of Investments [Line Items]
Amortized Cost	403,517	361,690
Fair Value	400,625	355,261
Common equity investments
Schedule of Investments [Line Items]
Amortized Cost	906,255	772,116
Fair Value	1,132,742	977,927
Joint ventures
Schedule of Investments [Line Items]
Amortized Cost	385,339	318,839
Fair Value	$ 364,428	$ 288,981

[1] As of December 31, 2022, the net estimated unrealized loss for U.S. federal income tax purposes was $126.2 million based on a tax cost basis of $13.1 billion. As of December 31, 2022, the estimated aggregate gross unrealized loss for U.S. federal income tax purposes was $382.2 million and the estimated aggregate gross unrealized gain for U.S. federal income tax purposes was $256.0 million.

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

[3] The amortized cost represents the original cost adjusted for the amortization or accretion of premium or discount , as applicable, on debt investments using the effective interest method.

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

[5] 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”.