Quarterly report pursuant to Section 13 or 15(d)

INVESTMENTS - Narrative (Details)

v3.24.1.u1
INVESTMENTS - Narrative (Details)
$ in Thousands
 1 Months Ended 2 Months Ended 6 Months Ended 12 Months Ended
Mar. 31, 2024
USD ($)
investment
industry
state
portfolioCompany
Feb. 29, 2024
USD ($)
Jan. 31, 2024
USD ($)
Dec. 31, 2023
USD ($)
Nov. 30, 2023
USD ($)
Mar. 31, 2024
USD ($)
investment
industry
state
portfolioCompany
Mar. 31, 2024
USD ($)
investment
industry
state
portfolioCompany
Mar. 31, 2023
USD ($)
Sep. 30, 2023
USD ($)
investment
Summary of Investment Holdings [Line Items]                  
Number of proprietary investments | investment 48         48 48   47
Fair Value $ 791,588         $ 791,588 $ 791,588   $ 704,815 [1]
Purchase of investments             102,733 $ 77,469  
Total             54,146   45,231
Cost $ 790,542         $ 790,542 $ 790,542   722,269 [1]
Number of investment portfolio company | portfolioCompany 51         51 51    
Number of states which have invested in the company location | state 24         24 24    
Number of industries that have made investments | industry 12         12 12    
Weighted average investment owned, at cost, amount $ 15,500         $ 15,500 $ 15,500   14,200
Gross receivables from portfolio companies 1,200         1,200 1,200   800
Allowance for uncollectible receivables 36         36 36   9
Quality Environmental Midco, Inc                  
Summary of Investment Holdings [Line Items]                  
Purchase of investments   $ 5,000     $ 11,000        
Total   3,000     2,000        
Cafe Zupas                  
Summary of Investment Holdings [Line Items]                  
Total         10,500        
Investment company, delayed draw term loan commitment         1,400        
Net proceeds from the sale of investments         7,300        
PIC 360, LLC                  
Summary of Investment Holdings [Line Items]                  
Realized investment gains         $ 300        
ALS Education, LLC                  
Summary of Investment Holdings [Line Items]                  
Purchase of investments       $ 14,300          
Leadpoint Business Services, LLC                  
Summary of Investment Holdings [Line Items]                  
Purchase of investments       12,000          
Salt & Straw, LLC                  
Summary of Investment Holdings [Line Items]                  
Purchase of investments       7,000          
Investment company, delayed draw term loan commitment       $ 2,900          
SpaceCo Holdings, LLC                  
Summary of Investment Holdings [Line Items]                  
Purchase of investments           13,500      
Perimeter Solutions Group                  
Summary of Investment Holdings [Line Items]                  
Purchase of investments   $ 15,000              
Trowbridge Chicago, LLC                  
Summary of Investment Holdings [Line Items]                  
Net proceeds from the sale of investments 8,400                
Realized investment gains 200                
Cost 300         300 300    
Investment company, prepayment fee 200                
CPM Holdings, Inc                  
Summary of Investment Holdings [Line Items]                  
Net proceeds from the sale of investments     $ 3,000            
Investment Portfolio Benchmark | Customer Concentration Risk | Five Largest Portfolio Investments                  
Summary of Investment Holdings [Line Items]                  
Fair Value 203,100         203,100 $ 203,100   $ 176,900
Concentration risk, percentage             25.70%   25.10%
Principal or Proprietary Transactions                  
Summary of Investment Holdings [Line Items]                  
Fair Value $ 783,900         $ 783,900 $ 783,900   $ 695,100
Principal or Proprietary Transactions | Investment Portfolio Benchmark | Investment Type Concentration Risk                  
Summary of Investment Holdings [Line Items]                  
Concentration risk, percentage             99.00%   98.60%
Syndicated Investments                  
Summary of Investment Holdings [Line Items]                  
Number of proprietary investments | investment 3         3 3   4
Fair Value $ 7,700         $ 7,700 $ 7,700   $ 9,700
Syndicated Investments | Investment Portfolio Benchmark | Investment Type Concentration Risk                  
Summary of Investment Holdings [Line Items]                  
Concentration risk, percentage             1.00%   1.40%
[1] Cumulative gross unrealized depreciation for federal income tax purposes is $56.9 million; cumulative gross unrealized appreciation for federal income tax purposes is $33.7 million. Cumulative net unrealized depreciation is $23.2 million, based on a tax cost of $728.0 million.