v3.25.2
Portfolio Investments - Schedule of Roll-forward of the Changes in Fair Value (Details) - USD ($)
$ in Thousands
 3 Months Ended 9 Months Ended
Jun. 30, 2025
Jun. 30, 2024
Jun. 30, 2025
Jun. 30, 2024
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]        
Fair value, beginning balance $ 4,178,869 $ 2,060,520 $ 3,140,726 $ 1,089,140
Purchases 853,200 730,189 2,189,516 1,792,067
Sales and repayments (130,216) (42,281) (440,750) (150,226)
Transfers in 603   37,816 10,757
Transfers out (32,423)   (68,859)  
Capitalized PIK interest income 2,287 2,370 7,438 5,409
Accretion of OID 4,080 3,062 15,940 9,359
Fair value, ending balance 4,910,435 2,752,013 4,910,435 2,752,013
Net unrealized appreciation (depreciation) relating to Level 3 assets still held and reported within net unrealized appreciation (depreciation) in the Consolidated Statement of Operations $ 32,786 $ (3,474) $ 34,314 $ (5,736)
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] Gain (Loss), Investment and Derivative, Operating, and Foreign Currency Transaction, after Tax Gain (Loss), Investment and Derivative, Operating, and Foreign Currency Transaction, after Tax Gain (Loss), Investment and Derivative, Operating, and Foreign Currency Transaction, after Tax Gain (Loss), Investment and Derivative, Operating, and Foreign Currency Transaction, after Tax
Net unrealized appreciation (depreciation)        
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]        
Net unrealized appreciation (depreciation)/Net realized gains (losses) $ 30,882 $ (1,861) $ 27,126 $ (4,692)
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] Non-control/Non-affiliate investments Non-control/Non-affiliate investments Non-control/Non-affiliate investments Non-control/Non-affiliate investments
Net realized gains (losses)        
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]        
Net unrealized appreciation (depreciation)/Net realized gains (losses) $ 3,153 $ 14 $ 1,482 $ 199
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] Non-control/Non-affiliate investments Non-control/Non-affiliate investments Non-control/Non-affiliate investments Non-control/Non-affiliate investments
Senior secured debt        
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]        
Fair value, beginning balance $ 3,893,763 $ 2,009,889 $ 2,890,580 $ 1,063,761
Purchases 767,295 541,256 2,074,529 1,577,752
Sales and repayments (129,693) (42,281) (439,936) (150,226)
Transfers in 0   36,264 10,757
Transfers out (31,820)   (68,256)  
Capitalized PIK interest income 1,504 1,803 5,198 4,011
Accretion of OID 3,950 2,979 15,549 9,275
Fair value, ending balance 4,535,534 2,511,476 4,535,534 2,511,476
Net unrealized appreciation (depreciation) relating to Level 3 assets still held and reported within net unrealized appreciation (depreciation) in the Consolidated Statement of Operations 29,553 (3,797) 26,990 (5,097)
Senior secured debt | Net unrealized appreciation (depreciation)        
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]        
Net unrealized appreciation (depreciation)/Net realized gains (losses) 27,382 (2,184) 20,035 (4,053)
Senior secured debt | Net realized gains (losses)        
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]        
Net unrealized appreciation (depreciation)/Net realized gains (losses) 3,153 14 1,571 199
Subordinated Debt        
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]        
Fair value, beginning balance 256,237 33,795 223,942 13,792
Purchases 85,708 188,809 114,790 207,980
Sales and repayments (266) 0 (557) 0
Transfers in 0   0 0
Transfers out 0   0  
Capitalized PIK interest income 783 567 2,240 1,398
Accretion of OID 130 83 391 84
Fair value, ending balance 342,885 223,319 342,885 223,319
Net unrealized appreciation (depreciation) relating to Level 3 assets still held and reported within net unrealized appreciation (depreciation) in the Consolidated Statement of Operations 293 65 2,079 65
Subordinated Debt | Net unrealized appreciation (depreciation)        
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]        
Net unrealized appreciation (depreciation)/Net realized gains (losses) 293 65 2,079 65
Subordinated Debt | Net realized gains (losses)        
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]        
Net unrealized appreciation (depreciation)/Net realized gains (losses) 0 0 0 0
Preferred equity        
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]        
Fair value, beginning balance 16,582 12,814 14,008 5,748
Purchases 162 0 162 6,211
Sales and repayments 0 0 0 0
Transfers in 603   1,552 0
Transfers out 0   0  
Capitalized PIK interest income 0 0 0 0
Accretion of OID 0 0 0 0
Fair value, ending balance 18,731 13,264 18,731 13,264
Net unrealized appreciation (depreciation) relating to Level 3 assets still held and reported within net unrealized appreciation (depreciation) in the Consolidated Statement of Operations 1,384 450 3,009 1,305
Preferred equity | Net unrealized appreciation (depreciation)        
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]        
Net unrealized appreciation (depreciation)/Net realized gains (losses) 1,384 450 3,009 1,305
Preferred equity | Net realized gains (losses)        
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]        
Net unrealized appreciation (depreciation)/Net realized gains (losses) 0 0 0 0
Common equity and warrants        
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]        
Fair value, beginning balance 12,287 4,022 12,196 5,839
Purchases 35 124 35 124
Sales and repayments (257) 0 (257) 0
Transfers in 0   0 0
Transfers out (603)   (603)  
Capitalized PIK interest income 0 0 0 0
Accretion of OID 0 0 0 0
Fair value, ending balance 13,285 3,954 13,285 3,954
Net unrealized appreciation (depreciation) relating to Level 3 assets still held and reported within net unrealized appreciation (depreciation) in the Consolidated Statement of Operations 1,556 (192) 2,236 (2,009)
Common equity and warrants | Net unrealized appreciation (depreciation)        
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]        
Net unrealized appreciation (depreciation)/Net realized gains (losses) 1,823 (192) 2,003 (2,009)
Common equity and warrants | Net realized gains (losses)        
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]        
Net unrealized appreciation (depreciation)/Net realized gains (losses) $ 0 $ 0 $ (89) $ 0