v3.26.1
Borrowings - Narrative (Details) - USD ($)
3 Months Ended 12 Months Ended
Oct. 02, 2025
Jun. 30, 2025
Dec. 27, 2024
Aug. 30, 2024
May 06, 2024
Apr. 24, 2024
Jan. 24, 2024
Oct. 04, 2023
Aug. 21, 2023
Mar. 31, 2026
Mar. 31, 2025
Mar. 18, 2025
Sep. 22, 2022
Dec. 31, 2025
Jan. 16, 2025
Oct. 22, 2024
Sep. 23, 2020
Sep. 22, 2020
Debt Instrument [Line Items]                                    
Covenant asset coverage ratio                                 150.00% 200.00%
Senior securities, amount                   $ 2,300,000,000                
Ratio of debt related expenses to average net assets attributable to common stock                   180.00%                
Interest rate (in percentage)           2.80%     3.60%     2.80%            
Short-term borrowings                   $ 0       $ 0        
Interest expense, short-term borrowings                   0 $ 0              
Secured borrowings                   0       0        
Borrowing interest expense                   0 400,000              
Secured debt average outstanding amount                   $ 0 $ 25,500,000              
Secured debt weighted average interest rate                     5.71%              
2024 Notes | Senior Notes                                    
Debt Instrument [Line Items]                                    
Debt instrument, face amount             $ 100,000,000.0                      
Debt instrument, interest rate, stated percentage             4.85%                      
Debt instrument, redemption price, percentage             100.00%                      
2026 Notes | Senior Notes                                    
Debt Instrument [Line Items]                                    
Debt instrument, face amount             $ 300,000,000.0                      
Debt instrument, interest rate, stated percentage             3.25%                      
Debt instrument, redemption price, percentage             100.00%                      
Restricted2026 Notes | Senior Notes                                    
Debt Instrument [Line Items]                                    
Debt instrument, redemption price, percentage                         99.88%          
2029 Notes | Senior Notes                                    
Debt Instrument [Line Items]                                    
Debt instrument, face amount         $ 300,000,000.0                     $ 400,000,000.0    
Debt instrument, interest rate, stated percentage         7.20%         7.20% 7.20%         7.20%    
Debt instrument, redemption price, percentage         100.00%                          
Debt instrument, additional aggregate principal amount                               $ 100,000,000.0    
2030 Notes | Senior Notes                                    
Debt Instrument [Line Items]                                    
Interest rate (in percentage) 2.515%                                  
Debt instrument, face amount $ 300,000,000.0                                  
Debt instrument, interest rate, stated percentage 6.00%                                  
Debt instrument, redemption price, percentage 100.00%                                  
Borrowing interest expense                   $ 4,500,000                
Revolving Credit Facility | Line of Credit                                    
Debt Instrument [Line Items]                                    
Aggregate borrowing capacity                   $ 2,830,000,000       3,130,000,000        
Weighted average annualized interest cost percentage                   5.83% 6.21%              
Average daily debt outstanding                   $ 2,200,000,000 $ 2,100,000,000              
Maximum debt outstanding                   2,600,000,000 $ 2,100,000,000              
Revolving Credit Facility | JPM Credit Facility | Line of Credit                                    
Debt Instrument [Line Items]                                    
Aggregate borrowing capacity   $ 1,050,000,000 $ 800,000,000.0       $ 400,000,000.0 $ 400,000,000.0   $ 1,050,000,000       1,050,000,000        
Interest rate (in percentage)   2.15% 2.25%       2.55% 2.75%   2.15% 2.25%              
Unused commitment fee               0.75%   0.55% 0.55%              
Maximum borrowing capacity, increase limit     $ 1,050,000,000       $ 800,000,000.0                      
Revolving Credit Facility | FBLC JPM Credit Facility | Line of Credit                                    
Debt Instrument [Line Items]                                    
Aggregate borrowing capacity             $ 400,000,000.0                      
Interest rate (in percentage)             2.80%                      
Maximum borrowing capacity, increase limit             $ 800,000,000.0                      
Revolving Credit Facility | FBLC JPM Credit Facility | Line of Credit | Minimum                                    
Debt Instrument [Line Items]                                    
Unused commitment fee             0.75%                      
Revolving Credit Facility | FBLC JPM Credit Facility | Line of Credit | Maximum                                    
Debt Instrument [Line Items]                                    
Unused commitment fee             3.00%                      
Revolving Credit Facility | JPM Revolver Facility | Line of Credit                                    
Debt Instrument [Line Items]                                    
Aggregate borrowing capacity             $ 505,000,000.0     $ 780,000,000       780,000,000        
Interest rate (in percentage)             1.98%     1.98% 1.98%              
Unused commitment fee             0.38%     0.38% 0.38%              
Revolving Credit Facility | JPM Revolver Facility Amendment | Line of Credit                                    
Debt Instrument [Line Items]                                    
Aggregate borrowing capacity                             $ 780,000,000.0      
Maximum borrowing capacity, increase limit                             $ 1,170,000,000      
Revolving Credit Facility | Wells Fargo Credit Facility | Line of Credit                                    
Debt Instrument [Line Items]                                    
Aggregate borrowing capacity             $ 300,000,000.0     $ 300,000,000       300,000,000        
Floor on interest rate             0.00%     0.00% 0.00%              
Interest rate (in percentage)       2.15%     2.75%     2.15% 2.15%              
Revolving Credit Facility | Wells Fargo Credit Facility | Line of Credit | Minimum                                    
Debt Instrument [Line Items]                                    
Unused commitment fee       0.50%     0.50%     0.50% 0.50%              
Revolving Credit Facility | Wells Fargo Credit Facility | Line of Credit | Maximum                                    
Debt Instrument [Line Items]                                    
Unused commitment fee       2.00%     2.00%     2.00% 2.00%              
Revolving Credit Facility | 2029 Notes | Line of Credit                                    
Debt Instrument [Line Items]                                    
Aggregate borrowing capacity                   $ 400,000,000       $ 400,000,000