Investments - Schedule of Investments and Cash and Cash Equivalents (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Sep. 30, 2022
Schedule Of Investment Income Reported Amounts By Category [Line Items]
Cash and cash equivalents	$ 50,155	$ 47,880
Cost
Schedule Of Investment Income Reported Amounts By Category [Line Items]
Total investments	1,198,096	1,177,357
Cash and cash equivalents	50,168	47,917
Total investments and cash and cash equivalents	1,248,264	1,225,274
Cost \| First lien
Schedule Of Investment Income Reported Amounts By Category [Line Items]
Total investments	819,839	838,842
Cost \| First lien in PSSL
Schedule Of Investment Income Reported Amounts By Category [Line Items]
Total investments	210,088	190,181
Cost \| Second lien
Schedule Of Investment Income Reported Amounts By Category [Line Items]
Total investments	1,113	1,113
Cost \| Equity
Schedule Of Investment Income Reported Amounts By Category [Line Items]
Total investments	77,018	65,715
Cost \| Equity interests in PSSL
Schedule Of Investment Income Reported Amounts By Category [Line Items]
Total investments	90,038	81,506
Fair Value
Schedule Of Investment Income Reported Amounts By Category [Line Items]
Total investments	1,164,032	1,164,254
Cash and cash equivalents	50,155	47,880
Total investments and cash and cash equivalents	1,214,187	1,212,134
Fair Value \| First lien
Schedule Of Investment Income Reported Amounts By Category [Line Items]
Total investments	796,608	819,461
Fair Value \| First lien in PSSL
Schedule Of Investment Income Reported Amounts By Category [Line Items]
Total investments	210,088	190,181
Fair Value \| Second lien
Schedule Of Investment Income Reported Amounts By Category [Line Items]
Total investments	149	147
Fair Value \| Equity
Schedule Of Investment Income Reported Amounts By Category [Line Items]
Total investments	105,567	105,031
Fair Value \| Equity interests in PSSL
Schedule Of Investment Income Reported Amounts By Category [Line Items]
Total investments	$ 51,620	$ 49,434

Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

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