Borrowings - Schedule of Maturities of Long-Term Debt (Details) - USD ($) $ in Thousands	Jun. 30, 2026	Sep. 30, 2025
Debt Instrument [Line Items]
Debt	$ 4,561,799	$ 4,926,778
Less Than 1 Year	949,462
1 – 3 Years	705,397
3 – 5 Years	1,509,740
More Than 5 Years	1,397,200
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	271,559
Less Than 1 Year	0
1 – 3 Years	0
3 – 5 Years	271,559
More Than 5 Years	0
Adviser Revolver
Debt Instrument [Line Items]
Debt	33,200
Less Than 1 Year	0
1 – 3 Years	0
3 – 5 Years	0
More Than 5 Years	33,200
2026 Notes
Debt Instrument [Line Items]
Debt	599,921
Less Than 1 Year	599,921
1 – 3 Years	0
3 – 5 Years	0
More Than 5 Years	0
2027 Notes
Debt Instrument [Line Items]
Debt	349,541
Less Than 1 Year	349,541
1 – 3 Years	0
3 – 5 Years	0
More Than 5 Years	0
2028 Notes
Debt Instrument [Line Items]
Debt	705,397
Less Than 1 Year	0
1 – 3 Years	705,397
3 – 5 Years	0
More Than 5 Years	0
2029 Notes
Debt Instrument [Line Items]
Debt	742,136
Less Than 1 Year	0
1 – 3 Years	0
3 – 5 Years	742,136
More Than 5 Years	0
2031 Notes
Debt Instrument [Line Items]
Debt	496,045
Less Than 1 Year	0
1 – 3 Years	0
3 – 5 Years	496,045
More Than 5 Years	$ 0