Consolidated Statements of Changes in Net Assets (unaudited) - USD ($) $ in Thousands	1 Months Ended		12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Investment Company, Net Assets [Roll Forward]
Beginning balance (in shares)			264,277,128	169,594,742	170,895,670
Beginning balance			$ 4,014,529	$ 2,547,878	$ 2,544,500
Issuance of common stock			$ 37,434	$ 1,526,351
Repurchases of common stock, net of commission costs (in shares)	(368,333)	(9,400)	(2,900,808)	(331,928)
Repurchases of common stock, net of commission costs	$ (5,165)	$ (137)	$ (40,631)	$ (4,809)	(16,861)
Net increase (decrease) in net assets resulting from operations
Net investment income after taxes			397,279	382,436	289,088
Net realized gain (loss) on investment transactions			(72,380)	(79,900)	(44,113)
Net realized gain (loss) on extinguishment of debt			(48)
Net change in unrealized appreciation (depreciation) on investment transactions			51,232	(29,371)	13,555
(Provision) benefit for taxes on realized gain on investments			0	0	(207)
(Provision) benefit for taxes on unrealized appreciation on investments			563	620	308
Distributions to stockholders:
Stock issued in connection with dividend reinvestment plan			33,704	44,283
Distributions from distributable earnings			(361,779)	(372,959)	(238,392)
Distributions from return of capital			(77,336)	0	0
Total increase (decrease) common stock, outstanding			$ (31,962)	$ 1,466,651	$ 3,378
Ending balance (in shares)	266,008,083	264,277,128	266,008,083	264,277,128	169,594,742
Ending balance	$ 3,982,567	$ 4,014,529	$ 3,982,567	$ 4,014,529	$ 2,547,878
Common Stock
Investment Company, Net Assets [Roll Forward]
Beginning balance (in shares)			264,277,128	169,594,742	170,895,670
Beginning balance			$ 264	$ 170	$ 171
Issuance of common stock (in shares)			2,408,940	92,115,308
Issuance of common stock			$ 3	$ 92
Repurchases of common stock, net of commission costs (in shares)			(2,900,808)	(331,928)	(1,300,928)
Repurchases of common stock, net of commission costs			$ (3)	$ (1)	$ (1)
Distributions to stockholders:
Stock issued in connection with dividend reinvestment plan (in shares)			2,222,823	2,899,006
Stock issued in connection with dividend reinvestment plan			$ 2	$ 3
Total increase (decrease) common stock, outstanding (in shares)			1,730,955	94,682,386	(1,300,928)
Total increase (decrease) common stock, outstanding			$ 2	$ 94	$ (1)
Ending balance (in shares)	266,008,083	264,277,128	266,008,083	264,277,128	169,594,742
Ending balance	$ 266	$ 264	$ 266	$ 264	$ 170
Paid in Capital in Excess of Par
Investment Company, Net Assets [Roll Forward]
Beginning balance			4,167,258	2,646,912	2,676,674
Issuance of common stock			37,431	1,526,259
Repurchases of common stock, net of commission costs			(40,628)	(4,808)	(16,860)
Distributions to stockholders:
Stock issued in connection with dividend reinvestment plan			33,702	44,280
Distributions from return of capital			(77,336)
Tax reclassification of stockholders' equity in accordance with generally accepted accounting principles			(89,310)	(45,385)	(12,902)
Total increase (decrease) common stock, outstanding			(136,141)	1,520,346	(29,762)
Ending balance	4,031,117	4,167,258	4,031,117	4,167,258	2,646,912
Distributable Earnings (Losses)
Investment Company, Net Assets [Roll Forward]
Beginning balance			(152,993)	(99,204)	(132,345)
Net increase (decrease) in net assets resulting from operations
Net investment income after taxes			397,279	382,436	289,088
Net realized gain (loss) on investment transactions			(72,380)	(79,900)	(44,113)
Net realized gain (loss) on extinguishment of debt			(48)
Net change in unrealized appreciation (depreciation) on investment transactions			51,232	(29,371)	13,555
(Provision) benefit for taxes on realized gain on investments					(207)
(Provision) benefit for taxes on unrealized appreciation on investments			563	620	308
Distributions to stockholders:
Distributions from distributable earnings			(361,779)	(372,959)	(238,392)
Tax reclassification of stockholders' equity in accordance with generally accepted accounting principles			89,310	45,385	12,902
Total increase (decrease) common stock, outstanding			104,177	(53,789)	33,141
Ending balance	$ (48,816)	$ (152,993)	$ (48,816)	$ (152,993)	$ (99,204)