v3.26.1
Fair Value and Maturity of Debt Outstanding - Schedule of Carrying Values and Estimated Fair Values of Debt Instruments (Details) - USD ($)
$ in Thousands
Jun. 30, 2026
Oct. 30, 2025
Jun. 30, 2025
Sep. 30, 2021
May 27, 2021
Debt Instrument [Line Items]          
Principal Outstanding $ 1,878,595   $ 2,103,554    
Net Carrying Value 1,860,649   2,088,311    
Fair Value $ 1,816,957   2,019,039    
3.364% 2026 Notes          
Debt Instrument [Line Items]          
Stated rate 3.364%        
3.437% 2028 Notes          
Debt Instrument [Line Items]          
Stated rate 3.437%        
5.50% 2030 Notes          
Debt Instrument [Line Items]          
Stated rate 5.50% 5.50%      
Public Notes          
Debt Instrument [Line Items]          
Unamortized Discount & Debt Issuance Costs $ 10,547   6,556    
Prospect Capital InterNotes®          
Debt Instrument [Line Items]          
Unamortized Discount & Debt Issuance Costs 7,399   8,687    
Credit Facility | Revolving Credit Facility          
Debt Instrument [Line Items]          
Principal Outstanding 562,328   856,322    
Unamortized Discount & Debt Issuance Costs 14,128   18,842    
Net Carrying Value 562,328   856,322    
Fair Value $ 562,328   $ 856,322    
Effective Interest Rate 2.05%   2.05%    
Unsecured Debt | 3.364% 2026 Notes          
Debt Instrument [Line Items]          
Stated rate 3.364%   3.364%   3.364%
Principal Outstanding $ 264,486   $ 300,000    
Unamortized Discount & Debt Issuance Costs 435   2,019    
Net Carrying Value 264,051   297,981    
Fair Value $ 261,169   $ 286,707    
Effective Interest Rate 3.89%   3.87%    
Unsecured Debt | 3.437% 2028 Notes          
Debt Instrument [Line Items]          
Stated rate 3.437%   3.437% 3.437%  
Principal Outstanding $ 254,749   $ 300,000    
Unamortized Discount & Debt Issuance Costs 2,743   4,537    
Net Carrying Value 252,006   295,463    
Fair Value $ 239,729   $ 268,671    
Effective Interest Rate 3.97%   3.93%    
Unsecured Debt | 5.50% 2030 Notes          
Debt Instrument [Line Items]          
Stated rate 5.50% 5.50%      
Principal Outstanding $ 182,153   $ 0    
Unamortized Discount & Debt Issuance Costs 7,369        
Net Carrying Value 174,784        
Fair Value $ 165,650        
Effective Interest Rate 6.76%        
Unsecured Debt | Public Notes          
Debt Instrument [Line Items]          
Principal Outstanding $ 701,388   600,000    
Net Carrying Value 690,841   593,444    
Fair Value 666,548   555,378    
Unsecured Debt | Prospect Capital InterNotes®          
Debt Instrument [Line Items]          
Principal Outstanding 614,879   647,232    
Unamortized Discount & Debt Issuance Costs 7,399   8,687    
Net Carrying Value 607,480   638,545    
Fair Value $ 588,081   $ 607,339    
Effective Interest Rate 6.04%   5.85%