Investments - Schedule of Investments and Cash and Cash Equivalents (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Sep. 30, 2021
Schedule Of Investment Income Reported Amounts By Category [Line Items]
Cash and cash equivalents (cost-$47,917 and $49,826, respectively)	$ 47,880	$ 49,826
Cost
Schedule Of Investment Income Reported Amounts By Category [Line Items]
Total investments	1,177,357	1,070,636
Cash and cash equivalents (cost-$47,917 and $49,826, respectively)	47,917	49,826
Total investments and cash and cash equivalents	1,225,274	1,120,462
Cost \| First lien
Schedule Of Investment Income Reported Amounts By Category [Line Items]
Total investments	838,842	795,263
Cost \| First lien in PSSL
Schedule Of Investment Income Reported Amounts By Category [Line Items]
Total investments	190,181	140,875
Cost \| Second lien
Schedule Of Investment Income Reported Amounts By Category [Line Items]
Total investments	1,113	8,937
Cost \| Equity
Schedule Of Investment Income Reported Amounts By Category [Line Items]
Total investments	65,715	65,186
Cost \| Equity interests in PSSL
Schedule Of Investment Income Reported Amounts By Category [Line Items]
Total investments	81,506	60,375
Fair Value
Schedule Of Investment Income Reported Amounts By Category [Line Items]
Total investments	1,164,254	1,081,619
Cash and cash equivalents (cost-$47,917 and $49,826, respectively)	47,880	49,826
Total investments and cash and cash equivalents	1,212,134	1,131,445
Fair Value \| First lien
Schedule Of Investment Income Reported Amounts By Category [Line Items]
Total investments	819,461	793,543
Fair Value \| First lien in PSSL
Schedule Of Investment Income Reported Amounts By Category [Line Items]
Total investments	190,181	140,875
Fair Value \| Second lien
Schedule Of Investment Income Reported Amounts By Category [Line Items]
Total investments	147	8,949
Fair Value \| Equity
Schedule Of Investment Income Reported Amounts By Category [Line Items]
Total investments	105,031	93,396
Fair Value \| Equity interests in PSSL
Schedule Of Investment Income Reported Amounts By Category [Line Items]
Total investments	$ 49,434	$ 44,856

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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