Consolidated Statements of Changes in Net Assets (unaudited) - USD ($) $ in Thousands	1 Months Ended					3 Months Ended		6 Months Ended
	Mar. 31, 2026	Jan. 31, 2026	Dec. 31, 2025	Oct. 31, 2025	Mar. 31, 2025	Mar. 31, 2026	Mar. 31, 2025	Mar. 31, 2026	Mar. 31, 2025
Investment Company, Net Assets [Roll Forward]
Beginning balance (in shares)				266,008,083				266,008,083
Beginning balance		$ 3,909,154		$ 3,982,567		$ 3,909,154	$ 4,017,544	$ 3,982,567	$ 4,014,529
Issuance of common stock							37,434		$ 37,434
Total number of shares repurchased (in shares)	(1,327,000)	(56,604)	(82,756)	(2,540,542)	(77,777)			(4,860,202)	(77,777)
Repurchases of common stock, net of commission costs	$ (16,343)	$ (765)	$ (1,115)	$ (34,792)	$ (1,130)	(27,801)	(1,130)	$ (63,708)	$ (1,130)
Net increase (decrease) in net assets resulting from operations:
Net investment income after taxes						85,547	98,662	181,305	195,252
Net realized gain (loss) on investment transactions						(10,355)	(11,041)	(14,193)	(38,896)
Net realized gain (loss) on extinguishment of debt									(48)
Net change in unrealized appreciation (depreciation) on investment transactions						(121,988)	(8,783)	(148,662)	33,792
Benefit for taxes on unrealized appreciation on investments						0	146	0	198
Distributions to stockholders:
Stock issued in connection with dividend reinvestment plan							15,150		33,704
Distributions from distributable earnings						(86,437)	(104,484)	(189,189)	(231,337)
Total increase (decrease) common stock, outstanding						$ (161,034)	$ 25,954	$ (234,447)	$ 28,969
Ending balance (in shares)	261,147,881				268,831,114	261,147,881	268,831,114	261,147,881	268,831,114
Ending balance	$ 3,748,120		$ 3,909,154		$ 4,043,498	$ 3,748,120	$ 4,043,498	$ 3,748,120	$ 4,043,498
Common Stock
Investment Company, Net Assets [Roll Forward]
Beginning balance (in shares)		263,384,785		266,008,083		263,384,785	265,498,597	266,008,083	264,277,128
Beginning balance		$ 263		$ 266		$ 263	$ 265	$ 266	$ 264
Issuance of common stock (in shares)							2,408,940		2,408,940
Issuance of common stock							$ 3		$ 3
Total number of shares repurchased (in shares)						(2,236,904)	(77,777)	(4,860,202)	(77,777)
Repurchases of common stock, net of commission costs						$ (2)		$ (5)
Distributions to stockholders:
Stock issued in connection with dividend reinvestment plan (in shares)							1,001,354		2,222,823
Stock issued in connection with dividend reinvestment plan							$ 1		$ 2
Total increase (decrease) common stock, outstanding (in shares)						(2,236,904)	3,332,517	(4,860,202)	4,553,986
Total increase (decrease) common stock, outstanding						$ (2)	$ 4	$ (5)	$ 5
Ending balance (in shares)	261,147,881		263,384,785		268,831,114	261,147,881	268,831,114	261,147,881	268,831,114
Ending balance	$ 261		$ 263		$ 269	$ 261	$ 269	$ 261	$ 269
Paid in Capital in Excess of Par
Investment Company, Net Assets [Roll Forward]
Beginning balance		3,995,213		4,031,117		3,995,213	4,185,811	4,031,117	4,167,258
Issuance of common stock							37,431		37,431
Repurchases of common stock, net of commission costs						(27,799)	(1,130)	(63,703)	(1,130)
Distributions to stockholders:
Stock issued in connection with dividend reinvestment plan							15,149		33,702
Total increase (decrease) common stock, outstanding						(27,799)	51,450	(63,703)	70,003
Ending balance	3,967,414		3,995,213		4,237,261	3,967,414	4,237,261	3,967,414	4,237,261
Distributable Earnings (Losses)
Investment Company, Net Assets [Roll Forward]
Beginning balance		$ (86,322)		$ (48,816)		(86,322)	(168,532)	(48,816)	(152,993)
Net increase (decrease) in net assets resulting from operations:
Net investment income after taxes						85,547	98,662	181,305	195,252
Net realized gain (loss) on investment transactions						(10,355)	(11,041)	(14,193)	(38,896)
Net realized gain (loss) on extinguishment of debt									(48)
Net change in unrealized appreciation (depreciation) on investment transactions						(121,988)	(8,783)	(148,662)	33,792
Benefit for taxes on unrealized appreciation on investments							146		198
Distributions to stockholders:
Distributions from distributable earnings						(86,437)	(104,484)	(189,189)	(231,337)
Total increase (decrease) common stock, outstanding						(133,233)	(25,500)	(170,739)	(41,039)
Ending balance	$ (219,555)		$ (86,322)		$ (194,032)	$ (219,555)	$ (194,032)	$ (219,555)	$ (194,032)