Quarterly report [Sections 13 or 15(d)]

INVESTMENTS - Narrative (Details)

v3.25.1
INVESTMENTS - Narrative (Details)
$ in Thousands
 1 Months Ended 6 Months Ended 12 Months Ended
Mar. 31, 2025
USD ($)
investment
state
industry
portfolioCompany
Feb. 28, 2025
USD ($)
Jan. 31, 2025
USD ($)
Dec. 31, 2024
USD ($)
Nov. 30, 2024
USD ($)
Oct. 31, 2024
USD ($)
Mar. 31, 2025
USD ($)
investment
state
industry
portfolioCompany
Mar. 31, 2024
USD ($)
Sep. 30, 2024
USD ($)
investment
Summary of Investment Holdings [Line Items]                  
Number of proprietary investments | investment 49           49   47
Fair Value $ 762,636           $ 762,636   $ 796,260 [1]
Purchase of investments             197,211 $ 102,733  
Financial support to investee, not provided $ 57,895           57,895   57,594
Principal repayments on investments             $ 157,784 $ 35,983  
Number of investment portfolio company | portfolioCompany 51           51    
Number of states which have invested in the company location | state 21           21    
Number of industries that have made investments | industry 14           14    
Weighted average investment owned, at cost, amount $ 15,500           $ 15,500   15,700
Uncollectible receivables allowance, minimum required day for uncollectible adjustment             90 days    
Gross receivables from portfolio companies 1,900           $ 1,900   1,700
Allowance for uncollectible receivables 94           94   75
Delayed draw term loans                  
Summary of Investment Holdings [Line Items]                  
Financial support to investee, not provided 13,200           13,200   14,150
Unused line of credit commitments                  
Summary of Investment Holdings [Line Items]                  
Financial support to investee, not provided 43,852           43,852   42,601
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         $ 28,900        
Wings ‘N More Restaurants, LLC                  
Summary of Investment Holdings [Line Items]                  
Purchase of investments         10,500        
Wings ‘N More Restaurants, LLC | Delayed draw term loans                  
Summary of Investment Holdings [Line Items]                  
Financial support to investee, not provided         5,000        
Wings ‘N More Restaurants, LLC | Unused line of credit commitments                  
Summary of Investment Holdings [Line Items]                  
Financial support to investee, not provided         1,500        
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              
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                
Dutch Gold Honey, Inc.                  
Summary of Investment Holdings [Line Items]                  
Purchase of investments   $ 18,900              
Investment Portfolio Benchmark | Customer Concentration Risk | Five Largest Portfolio Investments                  
Summary of Investment Holdings [Line Items]                  
Fair Value 186,800           $ 186,800   $ 232,700
Concentration risk, percentage             24.50%   29.20%
Principal or Proprietary Transactions                  
Summary of Investment Holdings [Line Items]                  
Fair Value $ 759,100           $ 759,100   $ 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%
Syndicated Investments                  
Summary of Investment Holdings [Line Items]                  
Number of proprietary investments | investment 2           2   2
Fair Value $ 3,500           $ 3,500   $ 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.