Investments - Investment Portfolio at Cost and Fair Value (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2023		Dec. 31, 2022
Schedule of Investments [Line Items]
Cost	$ 9,669,106		$ 9,657,872
Fair Value	$ 9,626,202		$ 9,617,248
Investment Owned, At Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments at Fair Value	100.00%		100.00%
First lien debt
Schedule of Investments [Line Items]
Cost	$ 9,508,358	[1],[2]	$ 9,497,570	[3],[4]
Fair Value	$ 9,425,003	[2]	$ 9,419,963	[4]
First lien debt | Investment Owned, At Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments at Fair Value	97.91%		97.95%
Second lien debt
Schedule of Investments [Line Items]
Cost	$ 49,200	[1],[2]	$ 48,753	[3],[4]
Fair Value	$ 46,678	[2]	$ 46,336	[4]
Second lien debt | Investment Owned, At Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments at Fair Value	0.48%		0.48%
Investments in equity
Schedule of Investments [Line Items]
Cost	$ 111,548		$ 111,549
Fair Value	$ 154,521		$ 150,949
Investments in equity | Investment Owned, At Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments at Fair Value	1.61%		1.57%

[1] The cost represents the original cost adjusted for the amortization of discounts and premiums, as applicable, on debt investments using the effective interest method in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”).

[2] Unless otherwise indicated, all 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. As of March 31, 2023, the Company had investments denominated in Canadian Dollars (CAD), Euros (EUR), British Pounds (GBP), Danish Krone (DKK), Swedish Krona (SEK), and Norwegian Krone (NOK). 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. The total par amount (in thousands) is presented for debt investments, while the number of shares or units (in whole amounts) owned is presented for equity investments. Each of the Company’s investments is pledged as collateral, under one or more of its credit facilities unless otherwise indicated.

[3] The cost represents the original cost adjusted for the amortization of discounts and premiums, as applicable, on debt investments using the effective interest method in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”).

[4] Unless otherwise indicated, all 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. As of December 31, 2022, the Company had investments denominated in Canadian Dollars (CAD), Euros (EUR), British Pounds (GBP), Danish Krone (DKK), Swedish Krona (SEK), and Norwegian Krone (NOK). 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. The total par amount (in thousands) is presented for debt investments, while the number of shares or units (in whole amounts) owned is presented for equity investments. Each of the Company’s investments is pledged as collateral, under one or more of its credit facilities unless otherwise indicated.