Annual report [Section 13 and 15(d), not S-K Item 405]

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
 12 Months Ended
Mar. 31, 2025
Mar. 31, 2024
Jan. 31, 2025
Oct. 31, 2023
Mar. 31, 2023
New investments, repayments and settlements:          
Cost $ 939,066 [1] $ 854,290 [2]      
Fair Value 979,320 [1] 920,504 [2]      
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  
Fair Value       $ 8,600  
PSI Molded Plastics, Inc          
New investments, repayments and settlements:          
Cost 16,400   $ 16,400    
Fair Value 9,800        
Total          
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]          
Beginning balance 974,345 920,486     $ 753,516
New investments, repayments and settlements:          
Issuances / originations 216,217 183,924      
Settlements / repayments (123,600) (28,000)      
Sales (75,982) (52,228)      
Transfers 0 0      
Ending balance 974,345 920,486      
Total | Debt and Equity Securities, Realized Gain (Loss)          
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]          
Total gain (loss) 63,163 29,964      
Total | Debt and Equity Securities, Unrealized Gain (Loss)          
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]          
Total gain (loss) 36,423 62,319      
Reversal of previously recorded (appreciation) depreciation upon realization (62,362) (29,009)      
Secured First Lien Debt          
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]          
Beginning balance 514,334 474,856     437,517
New investments, repayments and settlements:          
Issuances / originations 169,200 74,536      
Settlements / repayments (98,600) (28,000)      
Sales 0 0      
Transfers 0 0      
Ending balance 514,334 474,856      
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 (4,550)      
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) (31,122) (7,859)      
Reversal of previously recorded (appreciation) depreciation upon realization 0 3,212      
Secured Second Lien Debt          
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]          
Beginning balance 103,580 138,703     75,734
New investments, repayments and settlements:          
Issuances / originations 400 64,000      
Settlements / repayments (25,000) 0      
Sales 0 0      
Transfers (9,790) 0      
Ending balance 103,580 138,703      
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 (3,200)      
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) (733) (1,031)      
Reversal of previously recorded (appreciation) depreciation upon realization 0 3,200      
Preferred Equity          
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]          
Beginning balance 302,163 213,480     222,585
New investments, repayments and settlements:          
Issuances / originations 46,617 14,688      
Settlements / repayments 0 0      
Sales (26,390) (50,726)      
Transfers 9,790 (8,621)      
Ending balance 302,163 213,480      
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) 19,790 36,833      
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) 63,210 34,050      
Reversal of previously recorded (appreciation) depreciation upon realization (24,334) (35,329)      
Common Equity/ Equivalents          
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]          
Beginning balance 54,268 93,447     $ 17,680
New investments, repayments and settlements:          
Issuances / originations 0 30,700      
Settlements / repayments 0 0      
Sales (49,592) (1,502)      
Transfers 0 8,621      
Ending balance 54,268 93,447      
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) 43,373 881      
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) 5,068 37,159      
Reversal of previously recorded (appreciation) depreciation upon realization $ (38,028) $ (92)      
[1] Cumulative gross unrealized appreciation for federal income tax purposes is $183.3 million; cumulative gross unrealized depreciation for federal income tax purposes is $144.9 million. Cumulative net unrealized appreciation is $38.5 million, based on a tax cost of $940.9 million.
[2] 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.