v3.26.1
Borrowings - Schedule of Debt Securitization (Details) - USD ($)
$ in Thousands
 3 Months Ended 9 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Debt Instrument [Line Items]        
Net (gain)/loss related to fair value hedge $ 131 $ (260) $ 216 $ 2,487
Amortization of debt issuance costs $ 3,853 $ 2,131 10,054 5,305
Cash paid for interest expense [1]     $ 202,399 $ 100,141
Annualized average contractual interest rate swap and stated interest rate 5.90% 6.80% 6.00% 7.10%
2025-R Debt Securitization And 2023 Debt Securitization        
Debt Instrument [Line Items]        
Stated interest expense $ 7,220 $ 7,327 $ 22,057 $ 22,675
Accretion of discounts on notes issued 0 24 0 72
Amortization of debt issuance costs 151 112 450 336
Total interest and other debt financing expenses 7,371 7,463 22,507 23,083
Cash paid for interest expense $ 7,221 $ 7,340 $ 17,486 $ 23,721
Annualized average contractual interest rate swap and stated interest rate 5.20% 6.80% 5.30% 7.00%
Average outstanding balance $ 556,000 $ 434,000 $ 556,000 $ 434,000
2025 Debt Securitization        
Debt Instrument [Line Items]        
Stated interest expense 7,859 0 24,035 0
Amortization of debt issuance costs 124 0 372 0
Total interest and other debt financing expenses 7,983 0 24,407 0
Cash paid for interest expense $ 7,764 0 $ 19,041 0
Annualized average contractual interest rate swap and stated interest rate 5.30%   5.40%  
Average outstanding balance $ 599,090 0 $ 599,090 0
2026-B Debt Securitization        
Debt Instrument [Line Items]        
Stated interest expense 4,078 0 7,528 0
Amortization of debt issuance costs 42 0 78 0
Total interest and other debt financing expenses 4,120 0 7,606 0
Cash paid for interest expense $ 0 0 $ 0 0
Annualized average contractual interest rate swap and stated interest rate 4.90%   4.90%  
Average outstanding balance $ 335,000 0 $ 206,154 0
SMBC Credit Facility        
Debt Instrument [Line Items]        
Stated interest expense 13,838 16,370 53,358 29,911
Facility fees 1,707 366 3,736 1,801
Amortization of debt issuance costs 1,679 930 3,966 2,299
Total interest and other debt financing expenses 17,224 17,666 61,060 34,011
Cash paid for interest expense $ 18,491 $ 13,609 $ 57,350 $ 28,782
Annualized average contractual interest rate swap and stated interest rate 5.10% 6.00% 5.30% 5.90%
Average outstanding balance $ 1,082,714 $ 1,093,822 $ 1,351,513 $ 676,057
BANA Credit Facility        
Debt Instrument [Line Items]        
Stated interest expense 5,089 1,546 18,070 1,546
Facility fees 144 122 207 122
Amortization of debt issuance costs 168 91 505 91
Total interest and other debt financing expenses 5,401 1,759 18,782 1,759
Cash paid for interest expense $ 6,252 $ 0 $ 17,608 $ 0
Annualized average contractual interest rate swap and stated interest rate 5.30% 6.30% 5.40% 6.30%
Average outstanding balance $ 386,818 $ 97,626 $ 446,366 $ 32,542
2027 Notes        
Debt Instrument [Line Items]        
Stated interest expense 7,249 7,463 21,887 22,523
Amortization of debt issuance costs 450 423 1,350 1,296
Total interest and other debt financing expenses 7,333 7,660 22,301 27,521
Cash paid for interest expense $ (1,762) $ (1,073) $ 12,417 $ 14,887
Annualized average contractual interest rate swap and stated interest rate 6.20% 6.90% 6.40% 7.10%
Average outstanding balance $ 428,892 $ 427,049 $ 429,342 $ 427,840
2027 Notes | Interest rate swaps        
Debt Instrument [Line Items]        
Net contractual interest rate swap expense (586) (87) (1,410) 165
Net (gain)/loss related to fair value hedge 220 (139) 474 3,537
2028 Notes        
Debt Instrument [Line Items]        
Stated interest expense 6,812 0 20,438 0
Accretion of discounts on notes issued 270 0 811 0
Amortization of debt issuance costs 357 0 1,049 0
Total interest and other debt financing expenses 7,641 0 23,169 0
Cash paid for interest expense $ 6,792 0 $ 21,741 0
Annualized average contractual interest rate swap and stated interest rate 5.60%   5.70%  
Average outstanding balance $ 500,000 0 $ 500,000 0
2028 Notes | Interest rate swaps        
Debt Instrument [Line Items]        
Net contractual interest rate swap expense 202 0 871 0
2029 Notes        
Debt Instrument [Line Items]        
Stated interest expense 7,250 7,250 21,750 21,750
Accretion of discounts on notes issued 261 261 783 783
Amortization of debt issuance costs 314 284 941 866
Total interest and other debt financing expenses 8,337 9,073 25,466 27,299
Cash paid for interest expense $ 8,251 $ 9,048 $ 24,411 $ 27,172
Annualized average contractual interest rate swap and stated interest rate 6.30% 6.90% 6.40% 7.10%
Average outstanding balance $ 500,000 $ 500,000 $ 500,000 $ 500,000
2029 Notes | Interest rate swaps        
Debt Instrument [Line Items]        
Net contractual interest rate swap expense 601 1,399 2,249 4,951
Net (gain)/loss related to fair value hedge (89) (121) (257) (1,051)
2030 Notes        
Debt Instrument [Line Items]        
Stated interest expense 7,343 7,348 22,031 10,367
Accretion of discounts on notes issued 281 280 842 391
Amortization of debt issuance costs 299 291 897 417
Total interest and other debt financing expenses 7,399 8,252 22,618 11,519
Cash paid for interest expense $ 6,653 $ 5,579 $ 21,509 $ 5,579
Annualized average contractual interest rate swap and stated interest rate 5.50% 6.20% 5.60% 6.20%
Average outstanding balance $ 500,000 $ 500,000 $ 500,000 $ 232,601
2030 Notes | Interest rate swaps        
Debt Instrument [Line Items]        
Net contractual interest rate swap expense (524) 333 (1,152) 344
2031 Notes        
Debt Instrument [Line Items]        
Stated interest expense 7,000 0 11,822 0
Accretion of discounts on notes issued 272 0 457 0
Amortization of debt issuance costs 268 0 446 0
Total interest and other debt financing expenses 7,600 0 12,801 0
Cash paid for interest expense $ 5,929 0 $ 5,929 0
Annualized average contractual interest rate swap and stated interest rate 5.70%   5.70%  
Average outstanding balance $ 500,000 0 $ 280,220 0
2031 Notes | Interest rate swaps        
Debt Instrument [Line Items]        
Net contractual interest rate swap expense 60 0 76 0
Adviser Revolver        
Debt Instrument [Line Items]        
Stated interest expense 19 535 34 535
Cash paid for interest expense $ 15 $ 0 $ 15 $ 0
Annualized average contractual interest rate swap and stated interest rate 3.50% 4.10% 3.60% 4.10%
Average outstanding balance $ 2,104 $ 52,302 $ 1,269 $ 17,434
Other short-term borrowings        
Debt Instrument [Line Items]        
Stated interest expense 1,684 59 4,991 59
Cash paid for interest expense $ 1,714 $ 0 $ 4,892 $ 0
Annualized average contractual interest rate swap and stated interest rate 4.80% 5.50% 4.90% 5.50%
Average outstanding balance $ 141,699 $ 4,263 $ 136,995 $ 1,421
[1] Includes cash paid or received for contractual interest rate swaps, which may have different contractual settlement dates among the (i) fixed interest leg, (ii) floating interest leg and (iii) the debt instrument.