Quarterly report pursuant to Section 13 or 15(d)

INVESTMENTS - Schedule of Changes in Level 3 Fair Value Measurements of Investments (Details)

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INVESTMENTS - Schedule of Changes in Level 3 Fair Value Measurements of Investments (Details) - USD ($)
$ in Thousands
 1 Months Ended 3 Months Ended 9 Months Ended
Sep. 30, 2024
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2024
Dec. 31, 2023
Mar. 31, 2024
Sep. 30, 2023
Mar. 31, 2023
New investments, repayments and settlements:                
Cost   $ 1,021,741   $ 1,021,741   $ 854,290 [1]    
Fair Value   1,072,230   1,072,230   920,504 [1]    
Old World Christmas, Inc.                
New investments, repayments and settlements:                
Realized gain (loss) on preferred equity         $ 300      
SFEG Holdings, Inc                
New investments, repayments and settlements:                
Cost     $ 4,800   4,800      
Fair Value     8,600   8,600      
Total                
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]                
Beginning balance $ 853,307 1,067,230 902,786 1,067,230 902,786 920,486 $ 915,614 $ 753,516
New investments, repayments and settlements:                
Issuances / originations   182,094 68,200 202,192 182,988      
Settlements / repayments   (5,500) (27,500) (33,500) (27,500)      
Sales   0 (50,453) (48,503) (52,228)      
Transfers   0 0 0 0      
Ending balance 853,307 1,067,230 902,786 1,067,230 902,786      
Total | Debt and Equity Securities, Realized Gain (Loss)                
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]                
Total gain (loss)   0 43,459 42,284 44,614      
Total | Debt and Equity Securities, Unrealized Gain (Loss)                
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]                
Total gain (loss)   37,329 (2,968) 22,299 45,055      
Reversal of previously recorded (appreciation) depreciation upon realization   0 (43,566) (38,028) (43,659)      
Secured First Lien Debt                
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]                
Beginning balance 469,480 599,911 476,126 599,911 476,126 474,856 508,504 437,517
New investments, repayments and settlements:                
Issuances / originations   135,477 3,500 155,575 73,600      
Settlements / repayments   (5,500) (27,500) (8,500) (27,500)      
Sales   0 0 0 0      
Transfers   0 0 0 0      
Ending balance 469,480 599,911 476,126 599,911 476,126      
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 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)   454 (7,040) (22,020) (6,153)      
Reversal of previously recorded (appreciation) depreciation upon realization   0 (1,338) 0 (1,338)      
Secured Second Lien Debt                
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]                
Beginning balance 111,344 108,743 137,480 108,743 137,480 138,703 102,747 75,734
New investments, repayments and settlements:                
Issuances / originations   0 39,000 0 64,000      
Settlements / repayments   0 0 (25,000) 0      
Sales   0 0 0 0      
Transfers   0 0 0 0      
Ending balance 111,344 108,743 137,480 108,743 137,480      
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 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)   (2,601) (4,267) (4,960) (2,254)      
Reversal of previously recorded (appreciation) depreciation upon realization   0 0 0 0      
Preferred Equity                
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]                
Beginning balance 228,528 308,226 214,664 308,226 214,664 213,480 267,596 222,585
New investments, repayments and settlements:                
Issuances / originations   46,617 0 46,617 14,688      
Settlements / repayments   0 0 0 0      
Sales   0 (50,453) 0 (50,726)      
Transfers   0 (8,621) 0 (8,621)      
Ending balance 228,528 308,226 214,664 308,226 214,664      
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 43,459 0 43,732      
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)   33,081 4,911 48,129 35,234      
Reversal of previously recorded (appreciation) depreciation upon realization   0 (42,228) 0 (42,228)      
Common Equity/ Equivalents                
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]                
Beginning balance 43,955 50,350 74,516 50,350 74,516 $ 93,447 $ 36,767 $ 17,680
New investments, repayments and settlements:                
Issuances / originations   0 25,700 0 30,700      
Settlements / repayments   0 0 0 0      
Sales   0 0 (48,503) (1,502)      
Transfers   0 8,621 0 8,621      
Ending balance $ 43,955 50,350 74,516 50,350 74,516      
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)   0 0 42,284 882      
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)   6,395 3,428 1,150 18,228      
Reversal of previously recorded (appreciation) depreciation upon realization   $ 0 $ 0 $ (38,028) $ (93)      
[1] Cumulative gross unrealized appreciation for federal income tax purposes is $180.5 million; cumulative gross unrealized depreciation for federal income tax purposes is $115.8 million. Cumulative net unrealized appreciation is $64.7 million, based on a tax cost of $855.8 million.