Quarterly report [Sections 13 or 15(d)]

INVESTMENTS - Schedule of Fair Value Measurements Using Significant Unobservable Inputs (Details)

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INVESTMENTS - Schedule of Fair Value Measurements Using Significant Unobservable Inputs (Details) - USD ($)
$ in Thousands
 3 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Total    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance $ 854,013 $ 796,222
New investments, repayments and settlements:    
Issuances/originations 101,300 147,582
Settlements/repayments (51,312) (92,096)
Net proceeds from sales (2,240) (73,081)
Ending balance 897,837 794,460
Total | Net realized gain (loss)    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Total gain (loss) 1,678 57,724
Total | Net unrealized appreciation (depreciation) and Reversal of prior period net depreciation (appreciation) on realization    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Total gain (loss) (3,498) 12,118
Reversal of prior period net depreciation (appreciation) on realization (2,104) (54,009)
Secured First Lien Debt    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance 622,371 554,937
New investments, repayments and settlements:    
Issuances/originations 57,276 111,754
Settlements/repayments (31,767) (76,255)
Net proceeds from sales 0 0
Ending balance 647,576 586,409
Secured First Lien Debt | Net realized gain (loss)    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Total gain (loss) (112) (4,074)
Secured First Lien Debt | Net unrealized appreciation (depreciation) and Reversal of prior period net depreciation (appreciation) on realization    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Total gain (loss) (23) (3,534)
Reversal of prior period net depreciation (appreciation) on realization (169) 3,581
Secured second lien debt    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance 150,542 113,716
New investments, repayments and settlements:    
Issuances/originations 39,071 29,244
Settlements/repayments (19,545) (15,841)
Net proceeds from sales 0 0
Ending balance 170,662 127,234
Secured second lien debt | Net 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 | Net unrealized appreciation (depreciation) and Reversal of prior period net depreciation (appreciation) on realization    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Total gain (loss) 739 115
Reversal of prior period net depreciation (appreciation) on realization (145) 0
Unsecured debt    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance 333 32
New investments, repayments and settlements:    
Issuances/originations 13 322
Settlements/repayments 0 0
Net proceeds from sales 0 0
Ending balance 346 359
Unsecured debt | Net realized gain (loss)    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Total gain (loss) 0 0
Unsecured debt | Net unrealized appreciation (depreciation) and Reversal of prior period net depreciation (appreciation) on realization    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Total gain (loss) 0 5
Reversal of prior period net depreciation (appreciation) on realization 0 0
Preferred Equity    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance 31,214 31,346
New investments, repayments and settlements:    
Issuances/originations 4,940 6,262
Settlements/repayments 0 0
Net proceeds from sales 0 (9,450)
Ending balance 36,761 31,294
Preferred Equity | Net realized gain (loss)    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Total gain (loss) 0 2,450
Preferred Equity | Net unrealized appreciation (depreciation) and Reversal of prior period net depreciation (appreciation) on realization    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Total gain (loss) 607 3,136
Reversal of prior period net depreciation (appreciation) on realization 0 (2,450)
Common Equity/ Equivalents    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance 49,553 96,191
New investments, repayments and settlements:    
Issuances/originations 0 0
Settlements/repayments 0 0
Net proceeds from sales (2,240) (63,631)
Ending balance 42,492 49,164
Common Equity/ Equivalents | Net realized gain (loss)    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Total gain (loss) 1,790 59,348
Common Equity/ Equivalents | Net unrealized appreciation (depreciation) and Reversal of prior period net depreciation (appreciation) on realization    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Total gain (loss) (4,821) 12,396
Reversal of prior period net depreciation (appreciation) on realization $ (1,790) $ (55,140)