Portfolio Investments - Schedule of Portfolio Composition (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2025		Sep. 30, 2025
Schedule of Investments [Line Items]
Investment, cost	$ 7,429,166	[1]	$ 6,863,940	[2]
Total investments at fair value	$ 7,433,861	[1]	$ 6,899,031	[2]
% of Net Assets	159.40%		151.90%
United States
Schedule of Investments [Line Items]
Investment, cost	$ 6,304,204		$ 5,722,070
Total investments at fair value	6,269,708		5,718,209
United Kingdom
Schedule of Investments [Line Items]
Investment, cost	387,222		403,707
Total investments at fair value	399,192		414,953
Sweden
Schedule of Investments [Line Items]
Investment, cost	312,943		306,364
Total investments at fair value	319,689		313,062
Germany
Schedule of Investments [Line Items]
Investment, cost	137,414		176,834
Total investments at fair value	146,130		185,742
Netherlands
Schedule of Investments [Line Items]
Investment, cost	110,705		110,787
Total investments at fair value	116,453		116,216
Luxembourg
Schedule of Investments [Line Items]
Investment, cost	90,100		89,870
Total investments at fair value	95,396		94,947
Greece
Schedule of Investments [Line Items]
Investment, cost	54,682		0
Total investments at fair value	54,800		0
Costa Rica
Schedule of Investments [Line Items]
Investment, cost	16,582		16,522
Total investments at fair value	16,980		16,789
Switzerland
Schedule of Investments [Line Items]
Investment, cost	10,405		10,385
Total investments at fair value	10,332		10,305
Jamaica
Schedule of Investments [Line Items]
Investment, cost	4,757		4,757
Total investments at fair value	4,939		4,894
Australia
Schedule of Investments [Line Items]
Investment, cost	152		1,683
Total investments at fair value	242		1,809
Canada
Schedule of Investments [Line Items]
Investment, cost	0		20,961
Total investments at fair value	$ 0		$ 22,105
Investment Owned, At Cost | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments	100.00%		100.00%
Investment Owned, At Cost | Geographic Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments	100.00%		100.00%
Investment Owned, At Cost | Geographic Concentration Risk | United States
Schedule of Investments [Line Items]
% of Total Investments	84.87%		83.37%
Investment Owned, At Cost | Geographic Concentration Risk | United Kingdom
Schedule of Investments [Line Items]
% of Total Investments	5.21%		5.88%
Investment Owned, At Cost | Geographic Concentration Risk | Sweden
Schedule of Investments [Line Items]
% of Total Investments	4.21%		4.46%
Investment Owned, At Cost | Geographic Concentration Risk | Germany
Schedule of Investments [Line Items]
% of Total Investments	1.85%		2.58%
Investment Owned, At Cost | Geographic Concentration Risk | Netherlands
Schedule of Investments [Line Items]
% of Total Investments	1.49%		1.61%
Investment Owned, At Cost | Geographic Concentration Risk | Luxembourg
Schedule of Investments [Line Items]
% of Total Investments	1.21%		1.31%
Investment Owned, At Cost | Geographic Concentration Risk | Greece
Schedule of Investments [Line Items]
% of Total Investments	0.74%		0.00%
Investment Owned, At Cost | Geographic Concentration Risk | Costa Rica
Schedule of Investments [Line Items]
% of Total Investments	0.22%		0.24%
Investment Owned, At Cost | Geographic Concentration Risk | Switzerland
Schedule of Investments [Line Items]
% of Total Investments	0.14%		0.15%
Investment Owned, At Cost | Geographic Concentration Risk | Jamaica
Schedule of Investments [Line Items]
% of Total Investments	0.06%		0.07%
Investment Owned, At Cost | Geographic Concentration Risk | Australia
Schedule of Investments [Line Items]
% of Total Investments	0.00%		0.02%
Investment Owned, At Cost | Geographic Concentration Risk | Canada
Schedule of Investments [Line Items]
% of Total Investments	0.00%		0.31%
Investment Owned, At Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments	100.00%		100.00%
Investment Owned, At Fair Value | Geographic Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments	100.00%		100.00%
% of Net Assets	159.40%		151.90%
Investment Owned, At Fair Value | Geographic Concentration Risk | United States
Schedule of Investments [Line Items]
% of Total Investments	84.33%		82.89%
% of Net Assets	134.42%		125.89%
Investment Owned, At Fair Value | Geographic Concentration Risk | United Kingdom
Schedule of Investments [Line Items]
% of Total Investments	5.37%		6.01%
% of Net Assets	8.56%		9.14%
Investment Owned, At Fair Value | Geographic Concentration Risk | Sweden
Schedule of Investments [Line Items]
% of Total Investments	4.30%		4.54%
% of Net Assets	6.86%		6.89%
Investment Owned, At Fair Value | Geographic Concentration Risk | Germany
Schedule of Investments [Line Items]
% of Total Investments	1.97%		2.69%
% of Net Assets	3.13%		4.09%
Investment Owned, At Fair Value | Geographic Concentration Risk | Netherlands
Schedule of Investments [Line Items]
% of Total Investments	1.57%		1.68%
% of Net Assets	2.50%		2.56%
Investment Owned, At Fair Value | Geographic Concentration Risk | Luxembourg
Schedule of Investments [Line Items]
% of Total Investments	1.28%		1.38%
% of Net Assets	2.05%		2.09%
Investment Owned, At Fair Value | Geographic Concentration Risk | Greece
Schedule of Investments [Line Items]
% of Total Investments	0.74%		0.00%
% of Net Assets	1.18%		0.00%
Investment Owned, At Fair Value | Geographic Concentration Risk | Costa Rica
Schedule of Investments [Line Items]
% of Total Investments	0.23%		0.24%
% of Net Assets	0.36%		0.37%
Investment Owned, At Fair Value | Geographic Concentration Risk | Switzerland
Schedule of Investments [Line Items]
% of Total Investments	0.14%		0.15%
% of Net Assets	0.22%		0.23%
Investment Owned, At Fair Value | Geographic Concentration Risk | Jamaica
Schedule of Investments [Line Items]
% of Total Investments	0.07%		0.07%
% of Net Assets	0.11%		0.11%
Investment Owned, At Fair Value | Geographic Concentration Risk | Australia
Schedule of Investments [Line Items]
% of Total Investments	0.00%		0.03%
% of Net Assets	0.01%		0.04%
Investment Owned, At Fair Value | Geographic Concentration Risk | Canada
Schedule of Investments [Line Items]
% of Total Investments	0.00%		0.32%
% of Net Assets	0.00%		0.49%
Senior Secured Debt
Schedule of Investments [Line Items]
Investment, cost	$ 7,001,244		$ 6,414,699
Total investments at fair value	$ 6,997,991		$ 6,438,079
% of Net Assets	150.05%		141.75%
Senior Secured Debt | Investment Owned, At Cost | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments	94.25%		93.45%
Senior Secured Debt | Investment Owned, At Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments	94.14%		93.32%
Subordinated Debt
Schedule of Investments [Line Items]
Investment, cost	$ 402,276		$ 423,818
Total investments at fair value	$ 406,637		$ 429,299
% of Net Assets	8.72%		9.45%
Subordinated Debt | Investment Owned, At Cost | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments	5.41%		6.17%
Subordinated Debt | Investment Owned, At Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments	5.47%		6.22%
Preferred Equity
Schedule of Investments [Line Items]
Investment, cost	$ 14,303		$ 14,080
Total investments at fair value	$ 18,935		$ 18,658
% of Net Assets	0.41%		0.41%
Preferred Equity | Investment Owned, At Cost | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments	0.19%		0.21%
Preferred Equity | Investment Owned, At Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments	0.25%		0.27%
Common Equity and Warrants
Schedule of Investments [Line Items]
Investment, cost	$ 11,343		$ 11,343
Total investments at fair value	$ 10,298		$ 12,995
% of Net Assets	0.22%		0.29%
Common Equity and Warrants | Investment Owned, At Cost | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments	0.15%		0.17%
Common Equity and Warrants | Investment Owned, At Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments	0.14%		0.19%

[1] Non-Control/Non-Affiliate Investments are investments that are neither Control Investments nor Affiliate Investments. Control Investments generally are defined by the Investment Company Act of 1940, as amended (the “Investment Company Act”), as investments in companies in which the Company owns more than 25% of the voting securities and/or has the power to exercise control over the management or policies of the company. Affiliate Investments generally are defined by the Investment Company Act as investments in companies in which the Company owns between 5% and 25% of the voting securities.

[2] Non-Control/Non-Affiliate Investments are investments that are neither Control Investments nor Affiliate Investments. Control Investments generally are defined by the Investment Company Act as investments in companies in which the Company owns more than 25% of the voting securities and/or has the power to exercise control over the management or policies of the company. Affiliate Investments generally are defined by the Investment Company Act as investments in companies in which the Company owns between 5% and 25% of the voting securities.