Portfolio Investments - Schedule of Portfolio Composition (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Jun. 30, 2026	Sep. 30, 2025
Schedule of Investments [Line Items]
Investment, cost	$ 6,897,681	$ 6,863,940	[1]
Total investments at fair value	$ 6,796,814	$ 6,899,031	[1]
% of Net Assets	158.89%	151.90%
United States
Schedule of Investments [Line Items]
Investment, cost	$ 5,920,198	$ 5,722,070
Total investments at fair value	5,816,566	5,718,209
Sweden
Schedule of Investments [Line Items]
Investment, cost	320,933	306,364
Total investments at fair value	318,864	313,062
United Kingdom
Schedule of Investments [Line Items]
Investment, cost	259,043	403,707
Total investments at fair value	259,402	414,953
Germany
Schedule of Investments [Line Items]
Investment, cost	119,119	176,834
Total investments at fair value	122,602	185,742
Netherlands
Schedule of Investments [Line Items]
Investment, cost	101,319	110,787
Total investments at fair value	102,307	116,216
Luxembourg
Schedule of Investments [Line Items]
Investment, cost	70,913	89,870
Total investments at fair value	71,609	94,947
Greece
Schedule of Investments [Line Items]
Investment, cost	54,772	0
Total investments at fair value	54,103	0
Mexico
Schedule of Investments [Line Items]
Investment, cost	36,033	0
Total investments at fair value	36,036	0
Switzerland
Schedule of Investments [Line Items]
Investment, cost	10,442	10,385
Total investments at fair value	10,352	10,305
Jamaica
Schedule of Investments [Line Items]
Investment, cost	4,757	4,757
Total investments at fair value	4,902	4,894
Australia
Schedule of Investments [Line Items]
Investment, cost	152	1,683
Total investments at fair value	71	1,809
Canada
Schedule of Investments [Line Items]
Investment, cost	0	20,961
Total investments at fair value	0	22,105
Costa Rica
Schedule of Investments [Line Items]
Investment, cost	0	16,522
Total investments at fair value	$ 0	$ 16,789
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	85.83%	83.37%
Investment Owned, At Cost | Geographic Concentration Risk | Sweden
Schedule of Investments [Line Items]
% of Total Investments	4.65%	4.46%
Investment Owned, At Cost | Geographic Concentration Risk | United Kingdom
Schedule of Investments [Line Items]
% of Total Investments	3.76%	5.88%
Investment Owned, At Cost | Geographic Concentration Risk | Germany
Schedule of Investments [Line Items]
% of Total Investments	1.73%	2.58%
Investment Owned, At Cost | Geographic Concentration Risk | Netherlands
Schedule of Investments [Line Items]
% of Total Investments	1.47%	1.61%
Investment Owned, At Cost | Geographic Concentration Risk | Luxembourg
Schedule of Investments [Line Items]
% of Total Investments	1.03%	1.31%
Investment Owned, At Cost | Geographic Concentration Risk | Greece
Schedule of Investments [Line Items]
% of Total Investments	0.79%	0.00%
Investment Owned, At Cost | Geographic Concentration Risk | Mexico
Schedule of Investments [Line Items]
% of Total Investments	0.52%	0.00%
Investment Owned, At Cost | Geographic Concentration Risk | Switzerland
Schedule of Investments [Line Items]
% of Total Investments	0.15%	0.15%
Investment Owned, At Cost | Geographic Concentration Risk | Jamaica
Schedule of Investments [Line Items]
% of Total Investments	0.07%	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 Cost | Geographic Concentration Risk | Costa Rica
Schedule of Investments [Line Items]
% of Total Investments	0.00%	0.24%
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	158.89%	151.90%
Investment Owned, At Fair Value | Geographic Concentration Risk | United States
Schedule of Investments [Line Items]
% of Total Investments	85.58%	82.89%
% of Net Assets	136.00%	125.89%
Investment Owned, At Fair Value | Geographic Concentration Risk | Sweden
Schedule of Investments [Line Items]
% of Total Investments	4.69%	4.54%
% of Net Assets	7.45%	6.89%
Investment Owned, At Fair Value | Geographic Concentration Risk | United Kingdom
Schedule of Investments [Line Items]
% of Total Investments	3.82%	6.01%
% of Net Assets	6.06%	9.14%
Investment Owned, At Fair Value | Geographic Concentration Risk | Germany
Schedule of Investments [Line Items]
% of Total Investments	1.80%	2.69%
% of Net Assets	2.87%	4.09%
Investment Owned, At Fair Value | Geographic Concentration Risk | Netherlands
Schedule of Investments [Line Items]
% of Total Investments	1.51%	1.68%
% of Net Assets	2.39%	2.56%
Investment Owned, At Fair Value | Geographic Concentration Risk | Luxembourg
Schedule of Investments [Line Items]
% of Total Investments	1.05%	1.38%
% of Net Assets	1.67%	2.09%
Investment Owned, At Fair Value | Geographic Concentration Risk | Greece
Schedule of Investments [Line Items]
% of Total Investments	0.80%	0.00%
% of Net Assets	1.26%	0.00%
Investment Owned, At Fair Value | Geographic Concentration Risk | Mexico
Schedule of Investments [Line Items]
% of Total Investments	0.53%	0.00%
% of Net Assets	0.84%	0.00%
Investment Owned, At Fair Value | Geographic Concentration Risk | Switzerland
Schedule of Investments [Line Items]
% of Total Investments	0.15%	0.15%
% of Net Assets	0.24%	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	0.00%	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%
Investment Owned, At Fair Value | Geographic Concentration Risk | Costa Rica
Schedule of Investments [Line Items]
% of Total Investments	0.00%	0.24%
% of Net Assets	0.00%	0.37%
Senior Secured Debt
Schedule of Investments [Line Items]
Investment, cost	$ 6,382,331	$ 6,414,699
Total investments at fair value	$ 6,280,474	$ 6,438,079
% of Net Assets	146.82%	141.75%
Senior Secured Debt | Investment Owned, At Cost | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments	92.53%	93.45%
Senior Secured Debt | Investment Owned, At Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments	92.41%	93.32%
Subordinated Debt
Schedule of Investments [Line Items]
Investment, cost	$ 481,298	$ 423,818
Total investments at fair value	$ 481,229	$ 429,299
% of Net Assets	11.25%	9.45%
Subordinated Debt | Investment Owned, At Cost | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments	6.98%	6.17%
Subordinated Debt | Investment Owned, At Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments	7.08%	6.22%
Equity investment in EDL JV
Schedule of Investments [Line Items]
Investment, cost	$ 13,104	$ 0
Total investments at fair value	$ 13,148	$ 0
% of Net Assets	0.31%	0.00%
Equity investment in EDL JV | Investment Owned, At Cost | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments	0.19%	0.00%
Equity investment in EDL JV | Investment Owned, At Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments	0.19%	0.00%
Common Equity and Warrants
Schedule of Investments [Line Items]
Investment, cost	$ 11,028	$ 11,343
Total investments at fair value	$ 9,030	$ 12,995
% of Net Assets	0.21%	0.29%
Common Equity and Warrants | Investment Owned, At Cost | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments	0.16%	0.17%
Common Equity and Warrants | Investment Owned, At Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments	0.13%	0.19%
Preferred Equity
Schedule of Investments [Line Items]
Investment, cost	$ 9,920	$ 14,080
Total investments at fair value	$ 12,933	$ 18,658
% of Net Assets	0.30%	0.41%
Preferred Equity | Investment Owned, At Cost | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments	0.14%	0.21%
Preferred Equity | Investment Owned, At Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments	0.19%	0.27%

[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 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.