Quarterly report pursuant to Section 13 or 15(d)

INVESTMENTS - Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation (Details)

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INVESTMENTS - Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation (Details) - USD ($)
$ in Thousands
 3 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Total    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance $ 704,562 $ 643,160
New investments, repayments and settlements:    
Issuances/originations 59,209 12,157
Settlements/repayments (21,843) (25,549)
Net proceeds from sales (260) (7,978)
Transfers 0 0
Ending balance 749,717 619,194
Total | Debt and Equity Securities, Realized Gain (Loss)    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Total gain (loss) 259 4,900
Total | Debt and Equity Securities, Unrealized Gain (Loss)    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Total gain (loss) 8,073 (2,699)
Reversal of prior period net depreciation (appreciation) on realization (283) (4,797)
Secured first lien debt    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance 510,701 463,858
New investments, repayments and settlements:    
Issuances/originations 50,024 11,475
Settlements/repayments (21,119) (24,738)
Net proceeds from sales 0 0
Transfers 0 0
Ending balance 546,602 450,243
Secured first lien debt | Debt and Equity Securities, Realized Gain (Loss)    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Total gain (loss) 0 0
Secured first lien debt | Debt and Equity Securities, Unrealized Gain (Loss)    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Total gain (loss) 6,996 (455)
Reversal of prior period net depreciation (appreciation) on realization 0 103
Secured second lien debt    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance 127,854 115,928
New investments, repayments and settlements:    
Issuances/originations 185 182
Settlements/repayments (724) (811)
Net proceeds from sales 0 0
Transfers 0 0
Ending balance 126,571 114,755
Secured second lien debt | Debt and Equity Securities, Realized Gain (Loss)    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Total gain (loss) 0 0
Secured second lien debt | Debt and Equity Securities, Unrealized Gain (Loss)    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Total gain (loss) (744) (544)
Reversal of prior period net depreciation (appreciation) on realization 0 0
Unsecured debt    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance 24 55
New investments, repayments and settlements:    
Issuances/originations 0 0
Settlements/repayments 0 0
Net proceeds from sales 0 0
Transfers 0 0
Ending balance 23 45
Unsecured debt | Debt and Equity Securities, Realized Gain (Loss)    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Total gain (loss) 0 (95)
Unsecured debt | Debt and Equity Securities, Unrealized Gain (Loss)    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Total gain (loss) (1) (10)
Reversal of prior period net depreciation (appreciation) on realization 0 95
Preferred Equity    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance 26,855 27,046
New investments, repayments and settlements:    
Issuances/originations 9,000 0
Settlements/repayments 0 0
Net proceeds from sales 0 0
Transfers 0 0
Ending balance 29,722 26,140
Preferred Equity | Debt and Equity Securities, Realized Gain (Loss)    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Total gain (loss) 0 0
Preferred Equity | Debt and Equity Securities, Unrealized Gain (Loss)    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Total gain (loss) (6,133) (906)
Reversal of prior period net depreciation (appreciation) on realization 0 0
Common Equity/ Equivalents    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance 39,128 36,273
New investments, repayments and settlements:    
Issuances/originations 0 500
Settlements/repayments 0 0
Net proceeds from sales (260) (7,978)
Transfers 0 0
Ending balance 46,799 28,011
Common Equity/ Equivalents | Debt and Equity Securities, Realized Gain (Loss)    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Total gain (loss) 259 4,995
Common Equity/ Equivalents | Debt and Equity Securities, Unrealized Gain (Loss)    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Total gain (loss) 7,955 (784)
Reversal of prior period net depreciation (appreciation) on realization $ (283) $ (4,995)