Borrowings - Schedule of Maturities of Long-Term Debt (Details) - USD ($) $ in Thousands	Sep. 30, 2025	Sep. 30, 2024
Debt Instrument [Line Items]
Debt	$ 4,926,778	$ 4,624,791
Less Than 1 Year	599,524
1 – 3 Years	348,994
3 – 5 Years	2,575,060
More Than 5 Years	1,403,200
2024 Debt Securitization
Debt Instrument [Line Items]
Debt	1,364,000
Less Than 1 Year	0
1 – 3 Years	0
3 – 5 Years	0
More Than 5 Years	1,364,000
JPM Credit Facility
Debt Instrument [Line Items]
Debt	1,098,437
Less Than 1 Year	0
1 – 3 Years	0
3 – 5 Years	1,098,437
More Than 5 Years	0
2026 Notes
Debt Instrument [Line Items]
Debt	599,524
Less Than 1 Year	599,524
1 – 3 Years	0
3 – 5 Years	0
More Than 5 Years	0
2027 Notes
Debt Instrument [Line Items]
Debt	348,994
Less Than 1 Year	0
1 – 3 Years	348,994
3 – 5 Years	0
More Than 5 Years	0
2028 Notes
Debt Instrument [Line Items]
Debt	720,521
Less Than 1 Year	0
1 – 3 Years	0
3 – 5 Years	720,521
More Than 5 Years	0
2029 Notes
Debt Instrument [Line Items]
Debt	756,102
Less Than 1 Year	0
1 – 3 Years	0
3 – 5 Years	756,102
More Than 5 Years	0
Adviser Revolver
Debt Instrument [Line Items]
Debt	39,200
Less Than 1 Year	0
1 – 3 Years	0
3 – 5 Years	0
More Than 5 Years	$ 39,200