Consolidated Statements of Changes in Net Assets - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Statement of Stockholders' Equity [Abstract]
Net investment income	$ 46,051	$ 60,070	$ 65,533
Net realized gain (loss) on investments and debt	(52,460)	(33,833)	(151,805)
Net change in unrealized appreciation (depreciation) on investments	39,225	27,493	59,594
Net change in provision for taxes on realized gain (loss) on investments	26	186	(4,952)
Net change in provision for taxes on change in unrealized appreciation (depreciation) on investments	0	(680)	1,576
Net change in unrealized (appreciation) depreciation on debt	(116)	(4,385)	(3,753)
Net increase (decrease) in net assets resulting from operations	32,726	48,851	(33,807)
Distributions to stockholders:
Distribution of net investment income	(62,684)	(57,432)	(49,571)
Total distributios to stockholders	(62,684)	(57,432)	(49,571)
Capital transactions:
Net increase in net assets resulting from capital transactions	0	302	0
Proceeds from public offering	0	552	0
Offering costs	0	(250)	0
Net increase (decrease) in net assets	(29,958)	(8,279)	(83,378)
Net assets:
Beginning of year	493,908	502,187	585,565
End of year	$ 463,950	$ 493,908	$ 502,187
Capital share activity:
Shares of common stock issued from public offering	0	71,594	0
Shares of common stock repurchased	0	0	0