Federal Income Tax Matters - Schedule of Accumulated Earnings (Deficit) Book Basis, Income Tax (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Schedule of Investments [Abstract]
Undistributed ordinary income – tax basis	$ 39,466	$ 0	$ 0
Undistributed realized gains – tax basis	28,784	0	0
Net unrealized appreciation (depreciation) on investments	(204,442)	(82,787)	(217,673)
Other temporary differences	3,847	1,058	(10,909)
Total accumulated earnings (deficit) – book basis	$ (132,345)	$ (81,729)	$ (228,582)