v3.25.0.1
Financial Highlights (Details)
$ / shares in Units, $ in Thousands
 3 Months Ended
Dec. 31, 2024
USD ($)
$ / shares
shares
Dec. 31, 2023
USD ($)
$ / shares
shares
Sep. 30, 2024
USD ($)
shares
Sep. 30, 2023
USD ($)
Feb. 06, 2019
Feb. 05, 2019
Investment Company, Financial Highlights [Roll Forward]            
Net asset value at beginning of period (in dollars per share) $ 15.19 $ 15.02        
Distributions declared:            
From net investment income - after tax (in dollars per share) (0.48) (0.44)        
Net investment income - after tax (in dollars per share) 0.37 0.49        
Net realized gain (loss) on investment transactions (in dollars per share) (0.11) 0.01        
Net realized gain (loss) on extinguishment of debt (in dollars per share) 0.00 0        
Net change in unrealized appreciation (depreciation) on investment transactions (in dollars per share) 0.16 (0.05)        
Net asset value at end of period (in dollars per share) 15.13 15.03        
Per share market value at end of period (in dollars per share) $ 15.16 $ 15.10        
Total return based on market value 3.51% 5.90%        
Number of common shares outstanding (in shares) | shares 265,498,597 170,585,795 264,277,128      
Ratio of net investment income - after tax to average net assets 9.52% 13.00%        
Ratio of total expenses to average net assets 10.94% 10.10%        
Ratio of incentive fees to average net assets 0.45% 0.83%        
Ratio of income and excise taxes to average net assets (0.01%) 0.02%        
Ratio of net expenses (without incentive fees) to average net assets 10.49% 9.27%        
Total return based on average net asset value 2.77% 2.96%        
Total return based on average net asset value - annualized 10.98% 11.80%        
Net assets at end of period | $ $ 4,017,544 $ 2,563,918 $ 4,014,529 $ 2,547,878    
Average debt outstanding | $ $ 4,770,127 $ 3,078,186        
Average debt outstanding per share (in dollars per share) $ 17.97 $ 18.04        
Portfolio Turnover 21.33% 5.31%        
Asset coverage ratio 180.82% 182.44%        
Asset coverage ratio per unit (in dollars per unit) $ 1,808 $ 1,825        
Minimum asset coverage ratio required         1.50 1.50
2028 Notes            
Distributions declared:            
Average debt outstanding | $ $ 450,000 $ 132,065        
Average market value per unit (in dollars per share) $ 1,043 $ 819        
2029 Notes            
Distributions declared:            
Average debt outstanding | $ $ 647,283 $ 0        
Average market value per unit (in dollars per share) $ 993 $ 0        
2024 Notes            
Distributions declared:            
Average debt outstanding | $ $ 0 $ 500,000        
Average market value per unit (in dollars per share)   $ 989        
2026 Notes            
Distributions declared:            
Average debt outstanding | $ $ 600,000 $ 600,000        
Average market value per unit (in dollars per share) $ 951 $ 892        
2027 Notes            
Distributions declared:            
Average debt outstanding | $ $ 350,000 $ 350,000        
Average market value per unit (in dollars per share) $ 927 $ 864        
Dividend Reinvestment Plan (DRIP)            
Investment Company, Financial Highlights [Roll Forward]            
Net increase in net assets as a result of issuance of DRIP shares (in dollars per share) $ 0.00 $ 0.00