Quarterly report [Sections 13 or 15(d)]

INVESTMENTS - Narrative (Details)

v3.25.2
INVESTMENTS - Narrative (Details)
$ in Thousands
 1 Months Ended 9 Months Ended 12 Months Ended
Jun. 30, 2025
USD ($)
investment
industry
portfolioCompany
state
May 31, 2025
USD ($)
Apr. 30, 2025
USD ($)
Mar. 31, 2025
USD ($)
Feb. 28, 2025
USD ($)
Jan. 31, 2025
USD ($)
Dec. 31, 2024
USD ($)
Nov. 30, 2024
USD ($)
Oct. 31, 2024
USD ($)
Jun. 30, 2025
USD ($)
investment
industry
portfolioCompany
state
Jun. 30, 2024
USD ($)
Sep. 30, 2024
USD ($)
investment
Summary of Investment Holdings [Line Items]                        
Number of proprietary investments | investment 49                 49   47
Fair Value $ 751,260                 $ 751,260   $ 796,260 [1]
Purchase of investments                   270,163 $ 149,122  
Financial support to investee, not provided 48,669                 48,669   57,594
Principal repayments on investments                   239,258 $ 120,946  
Cost $ 777,851                 $ 777,851   771,011 [1]
Number of investment portfolio company | portfolioCompany 51                 51    
Number of states which have invested in the company location | state 22                 22    
Number of industries that have made investments | industry 14                 14    
Weighted average investment owned, at cost, amount $ 15,300                 $ 15,300   15,700
Uncollectible receivables allowance, minimum required day for uncollectible adjustment                   90 days    
Gross receivables from portfolio companies 2,400                 $ 2,400   1,700
Allowance for uncollectible receivables 100                 100   75
Unused line of credit commitments                        
Summary of Investment Holdings [Line Items]                        
Financial support to investee, not provided 40,326                 40,326   42,601
Delayed draw term loans                        
Summary of Investment Holdings [Line Items]                        
Financial support to investee, not provided 7,500                 7,500   14,150
Perimeter Solutions Group                        
Summary of Investment Holdings [Line Items]                        
Net proceeds from the sale of investments                 $ 15,000      
Prepayment fee income                 500      
Antenna Research Associates, Inc                        
Summary of Investment Holdings [Line Items]                        
Net proceeds from the sale of investments                 31,300      
Realized investment gains (losses)                 $ 59,300      
Giving Home Healthcare, LLC                        
Summary of Investment Holdings [Line Items]                        
Purchase of investments 7,000             $ 28,900        
Wings ‘N More Restaurants, LLC                        
Summary of Investment Holdings [Line Items]                        
Purchase of investments               10,500        
Wings ‘N More Restaurants, LLC | Unused line of credit commitments                        
Summary of Investment Holdings [Line Items]                        
Financial support to investee, not provided               1,500        
Wings ‘N More Restaurants, LLC | Delayed draw term loans                        
Summary of Investment Holdings [Line Items]                        
Financial support to investee, not provided               5,000        
ENET Holdings, LLC                        
Summary of Investment Holdings [Line Items]                        
Net proceeds from the sale of investments               $ 22,300        
Vet’s Choice Radiology, LLC                        
Summary of Investment Holdings [Line Items]                        
Purchase of investments             $ 42,800          
Pan-Am Dental, LLC                        
Summary of Investment Holdings [Line Items]                        
Purchase of investments             28,900          
Freedom Dental Management, Inc.                        
Summary of Investment Holdings [Line Items]                        
Purchase of investments             15,000          
Tube Bending Technology, LLC                        
Summary of Investment Holdings [Line Items]                        
Purchase of investments             5,000          
Gladstone Alternative                        
Summary of Investment Holdings [Line Items]                        
Purchase of investments             5,000          
Salt and Straw, LLC                        
Summary of Investment Holdings [Line Items]                        
Net proceeds from the sale of investments             10,900          
Prepayment fee income             100          
Realized investment gains (losses)             2,500          
DKI Ventures, LLC                        
Summary of Investment Holdings [Line Items]                        
Realized investment gains (losses)             $ (4,100)          
Fix-It Group, LLC                        
Summary of Investment Holdings [Line Items]                        
Net proceeds from the sale of investments           $ 20,600            
Prepayment fee income           100            
Sokol                        
Summary of Investment Holdings [Line Items]                        
Net proceeds from the sale of investments         $ 1,100 $ 5,400            
Realized investment gains (losses)         4,700              
Dutch Gold Honey, Inc.                        
Summary of Investment Holdings [Line Items]                        
Purchase of investments         18,900              
Viron                        
Summary of Investment Holdings [Line Items]                        
Purchase of investments         $ 19,400              
Viva Railings, LLC                        
Summary of Investment Holdings [Line Items]                        
Principal repayments on investments       $ 6,000                
MCG Energy Solutions, LLC                        
Summary of Investment Holdings [Line Items]                        
Net proceeds from the sale of investments       20,400                
Realized investment gains (losses)       $ 3,000                
SpaceCo Holdings, LLC                        
Summary of Investment Holdings [Line Items]                        
Net proceeds from the sale of investments     $ 42,200                  
Eegee Acquisition Corporation                        
Summary of Investment Holdings [Line Items]                        
Realized investment gains (losses)     4,400                  
Altior Healthcare, LLC                        
Summary of Investment Holdings [Line Items]                        
Net proceeds from the sale of investments   $ 46,000                    
Cafe Zupas                        
Summary of Investment Holdings [Line Items]                        
Net proceeds from the sale of investments 36,100                      
Prepayment fee income 400                      
RF Technologies, LLC                        
Summary of Investment Holdings [Line Items]                        
Purchase of investments 12,600                      
Financial support to investee, not provided 3,500                 3,500    
Investment Portfolio Benchmark | Customer Concentration Risk | Five Largest Portfolio Investments                        
Summary of Investment Holdings [Line Items]                        
Fair Value 189,700                 $ 189,700   $ 232,700
Concentration risk, percentage                   25.30%   29.20%
Principal or Proprietary Transactions                        
Summary of Investment Holdings [Line Items]                        
Fair Value 747,500                 $ 747,500   $ 792,900
Principal or Proprietary Transactions | Investment Portfolio Benchmark | Investment Type Concentration Risk                        
Summary of Investment Holdings [Line Items]                        
Concentration risk, percentage                   99.50%   99.60%
Secured First Lien Debt                        
Summary of Investment Holdings [Line Items]                        
Fair Value 529,149                 $ 529,149   $ 554,937
Cost 555,347                 555,347   580,736
Secured First Lien Debt | Eegee Acquisition Corporation                        
Summary of Investment Holdings [Line Items]                        
Cost     12,800                  
Common Equity/ Equivalents                        
Summary of Investment Holdings [Line Items]                        
Fair Value 51,741                 51,741   96,229
Cost $ 40,451                 $ 40,451   $ 31,369
Common Equity/ Equivalents | Eegee Acquisition Corporation                        
Summary of Investment Holdings [Line Items]                        
Cost     $ 8,500                  
Syndicated Investments                        
Summary of Investment Holdings [Line Items]                        
Number of proprietary investments | investment 2                 2   2
Fair Value $ 3,800                 $ 3,800   $ 3,300
Syndicated Investments | Investment Portfolio Benchmark | Investment Type Concentration Risk                        
Summary of Investment Holdings [Line Items]                        
Concentration risk, percentage                   0.50%   0.40%
[1] Cumulative gross unrealized depreciation for federal income tax purposes is $66.1 million; cumulative gross unrealized appreciation for federal income tax purposes is $85.8 million. Cumulative net unrealized appreciation is $19.7 million, based on a tax cost of $776.5 million.