Investments - Composition of the Company's Investment Portfolio, at Amortized Cost and Fair Value (with Corresponding Percentage of Total Portfolio Investments) (Details) - USD ($) $ in Thousands		9 Months Ended		12 Months Ended
		Sep. 30, 2024		Dec. 31, 2023
Investments
Amortized Cost:	[1]	$ 3,641,702		$ 2,523,064
Fair value	[1]	$ 3,662,029	[2]	$ 2,528,167	[3]
Concentration risk, percentage		100.00%		100.00%
Investment Owned, At Cost | Investment Type Concentration Risk
Investments
Concentration risk, percentage		100.00%		100.00%
Investment Owned, At Fair Value | Investment Type Concentration Risk
Investments
Concentration risk, percentage		100.00%		100.00%
Senior secured loans
Investments
Amortized Cost:		$ 3,127,700		$ 2,161,659
Fair value		$ 3,151,328		$ 2,171,243
Senior secured loans | Investment Owned, At Cost | Investment Type Concentration Risk
Investments
Concentration risk, percentage		85.90%		85.70%
Senior secured loans | Investment Owned, At Fair Value | Investment Type Concentration Risk
Investments
Concentration risk, percentage		86.10%		85.90%
Unitranche secured loans
Investments
Amortized Cost:		$ 165,972		$ 185,177
Fair value		$ 168,208		$ 184,853
Unitranche secured loans | Investment Owned, At Cost | Investment Type Concentration Risk
Investments
Concentration risk, percentage		4.60%		7.30%
Unitranche secured loans | Investment Owned, At Fair Value | Investment Type Concentration Risk
Investments
Concentration risk, percentage		4.60%		7.30%
Junior secured loans
Investments
Amortized Cost:		$ 172,128		$ 94,550
Fair value		$ 160,750		$ 87,986
Junior secured loans | Investment Owned, At Cost | Investment Type Concentration Risk
Investments
Concentration risk, percentage		4.70%		3.80%
Junior secured loans | Investment Owned, At Fair Value | Investment Type Concentration Risk
Investments
Concentration risk, percentage		4.30%		3.50%
Equity securities
Investments
Amortized Cost:		$ 175,902		$ 81,678
Fair value		$ 181,743		$ 84,085
Equity securities | Investment Owned, At Cost | Investment Type Concentration Risk
Investments
Concentration risk, percentage		4.80%		3.20%
Equity securities | Investment Owned, At Fair Value | Investment Type Concentration Risk
Investments
Concentration risk, percentage		5.00%		3.30%

[1] All of the Company’s investments are issued by eligible portfolio companies, as defined in the Investment Company Act of 1940, as amended, (the “1940 Act”), unless otherwise noted. All of the Company’s investments are issued by U.S. portfolio companies unless otherwise noted.

[2] Except as otherwise noted, because there is no readily available market value for these investments, the fair value of each of these investments is determined in good faith using significant unobservable inputs by the Valuation Designee. (See Note 4 in the accompanying notes to the consolidated financial statements).

[3] Except as otherwise noted, because there is no readily available market value for these investments, the fair value of each of these investments is determined in good faith using significant unobservable inputs by the Valuation Designee. (See Note 4 in the accompanying notes to the consolidated financial statements.)