Quarterly report pursuant to Section 13 or 15(d)

BORROWINGS - Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation (Details)

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BORROWINGS - Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation (Details) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Mar. 31, 2023
Mar. 31, 2022
Mar. 31, 2023
Mar. 31, 2022
Sep. 30, 2022
Debt Instrument [Line Items]          
Line of credit at fair value (Cost of $152,600 and $141,800, respectively) $ 152,439   $ 152,439   $ 141,800
Significant Unobservable Inputs (Level 3) | Fair Value, Recurring          
Debt Instrument [Line Items]          
Line of credit at fair value (Cost of $152,600 and $141,800, respectively) 152,439   152,439   $ 141,800
Significant Unobservable Inputs (Level 3) | Fair Value, Recurring | Long-Term Debt          
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]          
Beginning balance 108,400 $ 53,900 141,800 $ 50,500  
Borrowings 85,600 23,300 100,400 161,500  
Repayments (41,400) (59,800) (89,600) (194,600)  
Net unrealized appreciation (161) 0 (161) 0  
Ending balance $ 152,439 $ 17,400 $ 152,439 $ 17,400