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

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

v3.26.1
INVESTMENTS - Schedule of Changes in Level 3 Fair Value Measurements of Investments (Details) - USD ($)
$ in Thousands
 3 Months Ended 12 Months Ended
Mar. 31, 2026
Mar. 31, 2026
Mar. 31, 2025
Jun. 30, 2025
Jan. 31, 2025
Mar. 31, 2024
New investments, repayments and settlements:            
Cost $ 1,052,848 [1] $ 1,052,848 [1] $ 939,066 [2]      
Investments owned, fair value 1,309,248 [1] 1,309,248 [1] 979,320 [2]      
Old World Christmas, Inc.            
New investments, repayments and settlements:            
Realized gain on equity 3,500          
SFEG Holdings, Inc            
New investments, repayments and settlements:            
Cost         $ 16,400  
Investments owned, fair value         9,800  
Total            
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]            
Beginning balance 1,304,243 1,304,243 974,345     $ 920,486
New investments, repayments and settlements:            
Issuances / originations   173,616 216,217      
Settlements / repayments   (29,896) (123,600)      
Sales   (3,481) (75,982)      
Transfers   0 0      
Ending balance 1,304,243 1,304,243 974,345      
Total | Debt and Equity Securities, Realized Gain (Loss)            
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]            
Total gain (loss)   (26,457) 63,163      
Total | Debt and Equity Securities, Unrealized Gain (Loss)            
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]            
Total gain (loss)   197,012 36,423      
Reversal of previously recorded (appreciation) depreciation upon realization   19,104 (62,362)      
Secured First Lien Debt            
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]            
Beginning balance 570,602 570,602 514,334     474,856
New investments, repayments and settlements:            
Issuances / originations   126,516 169,200      
Settlements / repayments   (29,896) (98,600)      
Sales   0 0      
Transfers   (26,391) 0      
Ending balance 570,602 570,602 514,334      
Secured First Lien Debt | PSI Molded Plastics, Inc            
New investments, repayments and settlements:            
Cost       $ 10,600    
Secured First Lien Debt | Horizon Facilities Services, Inc.            
New investments, repayments and settlements:            
Cost         57,700  
Investments owned, fair value         $ 26,400  
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)   (29,938) 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)   (3,127) (31,122)      
Reversal of previously recorded (appreciation) depreciation upon realization   19,104 0      
Secured Second Lien Debt            
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]            
Beginning balance 99,197 99,197 103,580     138,703
New investments, repayments and settlements:            
Issuances / originations   1,800 400      
Settlements / repayments   0 (25,000)      
Sales   0 0      
Transfers   15,775 (9,790)      
Ending balance 99,197 99,197 103,580      
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)   (21,958) (733)      
Reversal of previously recorded (appreciation) depreciation upon realization   0 0      
Preferred Equity            
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]            
Beginning balance 426,949 426,949 302,163     213,480
New investments, repayments and settlements:            
Issuances / originations   45,300 46,617      
Settlements / repayments   0 0      
Sales   (3,481) (26,390)      
Transfers   10,616 9,790      
Ending balance 426,949 426,949 302,163      
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)   3,481 19,790      
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)   68,870 63,210      
Reversal of previously recorded (appreciation) depreciation upon realization   0 (24,334)      
Common Equity/ Equivalents            
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]            
Beginning balance 207,495 207,495 54,268     $ 93,447
New investments, repayments and settlements:            
Issuances / originations   0 0      
Settlements / repayments   0 0      
Sales   0 (49,592)      
Transfers   0 0      
Ending balance $ 207,495 207,495 54,268      
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 43,373      
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)   153,227 5,068      
Reversal of previously recorded (appreciation) depreciation upon realization   $ 0 $ (38,028)      
[1] Cumulative gross unrealized appreciation for federal income tax purposes is $428.5 million; cumulative gross unrealized depreciation for federal income tax purposes is $173.7 million. Cumulative net unrealized appreciation is $254.8 million, based on a tax cost of $1.1 billion.
[2] 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.