Fair Value Measurements - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Mar. 31, 2023	Mar. 31, 2022
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Net change in unrealized appreciation (depreciation) on investment transactions	$ (6,986)	$ 23,158	$ (46,608)	$ 27,393
Level 3
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Net change in unrealized appreciation (depreciation) on investment transactions	$ (10,572)	$ 14,133	$ (20,887)	$ 28,759