Quarterly report [Sections 13 or 15(d)]

CONSOLIDATED SCHEDULE OF INVESTMENTS IN AND ADVANCES TO AFFILIATES - Summary of Schedule of Investment (Details)

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CONSOLIDATED SCHEDULE OF INVESTMENTS IN AND ADVANCES TO AFFILIATES - Summary of Schedule of Investment (Details) - USD ($)
$ in Thousands
Mar. 31, 2025
Dec. 31, 2024
Mar. 31, 2024
Dec. 31, 2023
Investments in and Advances to Affiliates [Line Items]        
Investment cost $ 3,995,082 $ 3,708,877    
Investments, at fair value: $ 3,924,450 $ 3,659,978    
Control investments        
Investments in and Advances to Affiliates [Line Items]        
Investment owned, percent of net assets 5.78% 5.69%    
Investment cost $ 105,494 $ 104,916    
Investments, at fair value: $ 115,734 $ 113,179 $ 112,215 $ 115,004
Control investments | Majority Owned Control Investments        
Investments in and Advances to Affiliates [Line Items]        
Investment owned, percent of net assets 5.20% 5.10%    
Investment cost $ 83,081 $ 82,503    
Investments, at fair value: $ 103,964 $ 101,522 100,098 103,487
Control investments | Other Control Investments        
Investments in and Advances to Affiliates [Line Items]        
Investment owned, percent of net assets 0.58% 0.59%    
Investment cost $ 22,413 $ 22,413    
Investments, at fair value: 11,770 11,657 12,117 11,517
Control investments | Coronado Aesthetics, LLC        
Investments in and Advances to Affiliates [Line Items]        
Investments, at fair value: 47   283  
Control investments | Coronado Aesthetics, LLC | Majority Owned Control Investments | Preferred Stock        
Investments in and Advances to Affiliates [Line Items]        
Investments, at fair value: 47 69 282 260
Control investments | Coronado Aesthetics, LLC | Majority Owned Control Investments | Common Stock        
Investments in and Advances to Affiliates [Line Items]        
Investments, at fair value: 0 0 1 2
Control investments | Coronado Aesthetics, LLC | Medical Devices & Equipment | Majority Owned Control Investments        
Investments in and Advances to Affiliates [Line Items]        
Investment cost 250 250    
Investments, at fair value: $ 47 $ 69    
Control investments | Coronado Aesthetics, LLC | Medical Devices & Equipment | Majority Owned Control Investments | Common Stock        
Investments in and Advances to Affiliates [Line Items]        
Shares (in shares) 180,000 180,000    
Investment cost $ 0 $ 0    
Investments, at fair value: $ 0 $ 0    
Control investments | Coronado Aesthetics, LLC | Medical Devices & Equipment | Preferred Series A | Majority Owned Control Investments | Preferred Stock        
Investments in and Advances to Affiliates [Line Items]        
Shares (in shares) 5,000,000 5,000,000    
Investment cost $ 250 $ 250    
Investments, at fair value: 47 69    
Control investments | Gibraltar Business Capital, LLC        
Investments in and Advances to Affiliates [Line Items]        
Investments, at fair value: 58,900   57,931  
Control investments | Gibraltar Business Capital, LLC | Majority Owned Control Investments | Unsecured Debt        
Investments in and Advances to Affiliates [Line Items]        
Investments, at fair value: 36,790 36,212 34,518 34,478
Control investments | Gibraltar Business Capital, LLC | Majority Owned Control Investments | Member Units        
Investments in and Advances to Affiliates [Line Items]        
Investments, at fair value: 22,110 23,051 23,413 28,034
Control investments | Gibraltar Business Capital, LLC | Diversified Financial Services | Majority Owned Control Investments        
Investments in and Advances to Affiliates [Line Items]        
Investment cost 70,796 70,218    
Investments, at fair value: $ 58,900 $ 59,263    
Control investments | Gibraltar Business Capital, LLC | Diversified Financial Services | Majority Owned Control Investments | Unsecured Debt One        
Investments in and Advances to Affiliates [Line Items]        
Maturity Date 2026-09 2026-09    
Interest rate and floor, fixed 3.45% 3.45%    
Investment, interest rate, paid in kind 8.05% 8.05%    
Principal amount $ 27,104 $ 26,569    
Investment cost 26,899 26,337    
Investments, at fair value: $ 26,899 $ 26,337    
Control investments | Gibraltar Business Capital, LLC | Diversified Financial Services | Majority Owned Control Investments | Unsecured Debt Two        
Investments in and Advances to Affiliates [Line Items]        
Maturity Date 2026-09 2026-09    
Interest rate and floor, fixed 11.95% 11.95%    
Principal amount $ 10,000 $ 10,000    
Investment cost 9,891 9,875    
Investments, at fair value: $ 9,891 $ 9,875    
Control investments | Gibraltar Business Capital, LLC | Diversified Financial Services | Majority Owned Control Investments | Member Units        
Investments in and Advances to Affiliates [Line Items]        
Shares (in shares) 1 1    
Investment cost $ 34,006 $ 34,006    
Investments, at fair value: 22,110 23,051    
Control investments | Hercules Adviser LLC        
Investments in and Advances to Affiliates [Line Items]        
Investments, at fair value: 45,017   41,884  
Control investments | Hercules Adviser LLC | Majority Owned Control Investments | Unsecured Debt        
Investments in and Advances to Affiliates [Line Items]        
Investments, at fair value: 0 12,000 12,000 12,000
Control investments | Hercules Adviser LLC | Majority Owned Control Investments | Member Units        
Investments in and Advances to Affiliates [Line Items]        
Investments, at fair value: 45,017 30,190 29,884 28,713
Control investments | Hercules Adviser LLC | Diversified Financial Services | Majority Owned Control Investments        
Investments in and Advances to Affiliates [Line Items]        
Investment cost 12,035 12,035    
Investments, at fair value: $ 45,017 $ 42,190    
Control investments | Hercules Adviser LLC | Diversified Financial Services | Majority Owned Control Investments | Unsecured Debt        
Investments in and Advances to Affiliates [Line Items]        
Maturity Date   2025-06    
Interest rate and floor, fixed   5.00%    
Principal amount   $ 12,000    
Investment cost   12,000    
Investments, at fair value:   $ 12,000    
Control investments | Hercules Adviser LLC | Diversified Financial Services | Majority Owned Control Investments | Member Units        
Investments in and Advances to Affiliates [Line Items]        
Shares (in shares) 1 1    
Investment cost $ 12,035 $ 35    
Investments, at fair value: 45,017 30,190    
Control investments | Tectura Corporation        
Investments in and Advances to Affiliates [Line Items]        
Investments, at fair value: 11,770   12,117  
Control investments | Tectura Corporation | Other Control Investments | Preferred Stock        
Investments in and Advances to Affiliates [Line Items]        
Investments, at fair value: 3,736 3,623 3,856 3,263
Control investments | Tectura Corporation | Other Control Investments | Common Stock        
Investments in and Advances to Affiliates [Line Items]        
Investments, at fair value: 2 7 11 4
Control investments | Tectura Corporation | Other Control Investments | Senior Secured Debt        
Investments in and Advances to Affiliates [Line Items]        
Investments, at fair value: 8,032 8,027 $ 8,250 $ 8,250
Control investments | Tectura Corporation | Consumer & Business Services | Other Control Investments        
Investments in and Advances to Affiliates [Line Items]        
Investment cost 22,413 22,413    
Investments, at fair value: $ 11,770 $ 11,657    
Control investments | Tectura Corporation | Consumer & Business Services | Other Control Investments | Common Stock        
Investments in and Advances to Affiliates [Line Items]        
Shares (in shares) 414,994,863 414,994,863    
Investment cost $ 900 $ 900    
Investments, at fair value: $ 2 $ 7    
Control investments | Tectura Corporation | Consumer & Business Services | Other Control Investments | Senior Secured Debt        
Investments in and Advances to Affiliates [Line Items]        
Maturity Date 2027-01 2027-01    
Interest rate and floor, fixed 8.25% 8.25%    
Principal amount $ 8,250 $ 8,250    
Investment cost 8,250 8,250    
Investments, at fair value: $ 8,032 $ 8,027    
Control investments | Tectura Corporation | Consumer & Business Services | Preferred Series BB | Other Control Investments | Preferred Stock        
Investments in and Advances to Affiliates [Line Items]        
Shares (in shares) 1,000,000 1,000,000    
Investment cost $ 0 $ 0    
Investments, at fair value: $ 7 $ 17    
Control investments | Tectura Corporation | Consumer & Business Services | Series C Preferred Stock | Other Control Investments | Preferred Stock        
Investments in and Advances to Affiliates [Line Items]        
Shares (in shares) 3,235,298 3,235,298    
Investment cost $ 13,263 $ 13,263    
Investments, at fair value: $ 3,729 $ 3,606