Quarterly report pursuant to Section 13 or 15(d)

CONSOLIDATED SCHEDULE OF INVESTMENTS IN AND ADVANCES TO AFFILIATES - Summary of schedule of investment - Parenthetical (Details)

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CONSOLIDATED SCHEDULE OF INVESTMENTS IN AND ADVANCES TO AFFILIATES - Summary of schedule of investment - Parenthetical (Details) - USD ($)
$ in Thousands
Mar. 31, 2024
Dec. 31, 2023
Mar. 31, 2023
Dec. 31, 2022
Investments in and Advances to Affiliates [Line Items]        
Investment cost $ 3,574,576 $ 3,247,033    
Investments, at fair value: $ 3,571,641 $ 3,248,046    
Control investments        
Investments in and Advances to Affiliates [Line Items]        
Investment owned, percent of net assets 5.95% 6.38%    
Investment cost $ 103,223 $ 103,182    
Investments, at fair value: $ 112,215 $ 115,004 $ 85,326 $ 76,458
Control investments | Majority Owned Control Investments        
Investments in and Advances to Affiliates [Line Items]        
Investment owned, percent of net assets 5.31% 5.74%    
Investment cost $ 80,810 $ 80,769    
Investments, at fair value: $ 100,098 $ 103,487 77,552 68,416
Control investments | Other Control Investments        
Investments in and Advances to Affiliates [Line Items]        
Investment owned, percent of net assets 0.64% 0.64%    
Investment cost $ 22,413 $ 22,413    
Investments, at fair value: 12,117 11,517 7,774 8,042
Control investments | Coronado Aesthetics, LLC        
Investments in and Advances to Affiliates [Line Items]        
Investments, at fair value: 283   256  
Control investments | Coronado Aesthetics, LLC | Majority Owned Control Investments | Preferred Stock        
Investments in and Advances to Affiliates [Line Items]        
Investments, at fair value: 282 260 253 313
Control investments | Coronado Aesthetics, LLC | Majority Owned Control Investments | Common Stock        
Investments in and Advances to Affiliates [Line Items]        
Investments, at fair value: 1 2 3 6
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: $ 283 $ 262    
Control investments | Coronado Aesthetics, LLC | Medical Devices & Equipment | Majority Owned Control Investments | Common Stock        
Investments in and Advances to Affiliates [Line Items]        
Shares 180,000 180,000    
Investment cost $ 0 $ 0    
Investments, at fair value: $ 1 $ 2    
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 5,000,000 5,000,000    
Investment cost $ 250 $ 250    
Investments, at fair value: 282 260    
Control investments | Gibraltar Business Capital, LLC        
Investments in and Advances to Affiliates [Line Items]        
Investments, at fair value: 57,931   40,701  
Control investments | Gibraltar Business Capital, LLC | Majority Owned Control Investments | Unsecured Debt        
Investments in and Advances to Affiliates [Line Items]        
Investments, at fair value: 34,518 34,478 24,589 21,700
Control investments | Gibraltar Business Capital, LLC | Majority Owned Control Investments | Preferred Stock        
Investments in and Advances to Affiliates [Line Items]        
Investments, at fair value:     14,942 14,137
Control investments | Gibraltar Business Capital, LLC | Majority Owned Control Investments | Common Stock        
Investments in and Advances to Affiliates [Line Items]        
Investments, at fair value:     1,170 1,107
Control investments | Gibraltar Business Capital, LLC | Majority Owned Control Investments | Member Units        
Investments in and Advances to Affiliates [Line Items]        
Investments, at fair value: 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 68,525 68,484    
Investments, at fair value: $ 57,931 $ 62,512    
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 11.50% 11.50%    
Principal amount $ 25,000 $ 25,000    
Investment cost 24,689 24,663    
Investments, at fair value: $ 24,689 $ 24,663    
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 9,830 9,815    
Investments, at fair value: $ 9,829 $ 9,815    
Control investments | Gibraltar Business Capital, LLC | Diversified Financial Services | Majority Owned Control Investments | Member Units        
Investments in and Advances to Affiliates [Line Items]        
Shares 1 1    
Investment cost $ 34,006 $ 34,006    
Investments, at fair value: 23,413 28,034    
Control investments | Hercules Adviser LLC        
Investments in and Advances to Affiliates [Line Items]        
Investments, at fair value: 41,884   36,595  
Control investments | Hercules Adviser LLC | Majority Owned Control Investments | Unsecured Debt        
Investments in and Advances to Affiliates [Line Items]        
Investments, at fair value: 12,000 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: 29,884 28,713 24,595 19,153
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: $ 41,884 $ 40,713    
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 2025-06    
Interest rate and floor, fixed 5.00% 5.00%    
Principal amount $ 12,000 $ 12,000    
Investment cost 12,000 12,000    
Investments, at fair value: $ 12,000 $ 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 1 1    
Investment cost $ 35 $ 35    
Investments, at fair value: 29,884 28,713    
Control investments | Tectura Corporation        
Investments in and Advances to Affiliates [Line Items]        
Investments, at fair value: 12,117   7,774  
Control investments | Tectura Corporation | Other Control Investments | Senior Secured Debt        
Investments in and Advances to Affiliates [Line Items]        
Investments, at fair value: 8,250 8,250 $ 7,774 8,042
Control investments | Tectura Corporation | Other Control Investments | Preferred Stock        
Investments in and Advances to Affiliates [Line Items]        
Investments, at fair value: 3,856 3,263   0
Control investments | Tectura Corporation | Other Control Investments | Common Stock        
Investments in and Advances to Affiliates [Line Items]        
Investments, at fair value: 11 4   $ 0
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: $ 12,117 $ 11,517    
Control investments | Tectura Corporation | Consumer & Business Services | Other Control Investments | Senior Secured Debt        
Investments in and Advances to Affiliates [Line Items]        
Maturity Date 2024-07 2024-07    
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: $ 8,250 $ 8,250    
Control investments | Tectura Corporation | Consumer & Business Services | Other Control Investments | Common Stock        
Investments in and Advances to Affiliates [Line Items]        
Shares 414,994,863 414,994,863    
Investment cost $ 900 $ 900    
Investments, at fair value: $ 11 $ 4    
Control investments | Tectura Corporation | Consumer & Business Services | Preferred Series BB | Other Control Investments | Preferred Stock        
Investments in and Advances to Affiliates [Line Items]        
Shares 1,000,000 1,000,000    
Investment cost $ 0 $ 0    
Investments, at fair value: $ 24 $ 12    
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 3,235,298 3,235,298    
Investment cost $ 13,263 $ 13,263    
Investments, at fair value: $ 3,832 $ 3,251