| COMMITMENTS AND CONTINGENCIES - Schedule of Principal Balances of Unused Line of Credit and Delayed Draw Term Debt Commitments and Guaranties (Details) - USD ($) $ in Thousands | 9 Months Ended | 12 Months Ended | 
|---|---|---|
| Jun. 30, 2023 | Sep. 30, 2022 | |
| Other Commitments [Line Items] | ||
| Total | $ 63,908 | $ 74,846 | 
| Unused line of credit commitments | ||
| Other Commitments [Line Items] | ||
| Total | 35,076 | 36,225 | 
| Delayed draw term loans | ||
| Other Commitments [Line Items] | ||
| Total | 27,989 | 37,778 | 
| Uncalled capital commitment | ||
| Other Commitments [Line Items] | ||
| Total | $ 843 | $ 843 | 
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