Borrowings - Schedule of Maturities of Long-Term Debt (Details) - USD ($) $ in Thousands	Mar. 31, 2026	Sep. 30, 2025
Debt Instrument [Line Items]
Debt	$ 4,723,905	$ 4,926,778
Less Than 1 Year	949,147
1 – 3 Years	712,928
3 – 5 Years	1,697,830
More Than 5 Years	1,364,000
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	947,674
Less Than 1 Year	0
1 – 3 Years	0
3 – 5 Years	947,674
More Than 5 Years	0
2026 Notes
Debt Instrument [Line Items]
Debt	599,789
Less Than 1 Year	599,789
1 – 3 Years	0
3 – 5 Years	0
More Than 5 Years	0
2027 Notes
Debt Instrument [Line Items]
Debt	349,358
Less Than 1 Year	349,358
1 – 3 Years	0
3 – 5 Years	0
More Than 5 Years	0
2028 Notes
Debt Instrument [Line Items]
Debt	712,928
Less Than 1 Year	0
1 – 3 Years	712,928
3 – 5 Years	0
More Than 5 Years	0
2029 Notes
Debt Instrument [Line Items]
Debt	750,156
Less Than 1 Year	0
1 – 3 Years	0
3 – 5 Years	750,156
More Than 5 Years	$ 0