Borrowings - 2027 Notes (Narrative) (Details) - USD ($) $ in Thousands	Aug. 03, 2021	Sep. 30, 2025	Sep. 30, 2024
Debt Instrument [Line Items]
Long-term debt		$ 4,900,773	$ 4,599,430
2027 Notes
Debt Instrument [Line Items]
Debt instrument, face amount	$ 350,000
Long-term debt		$ 350,000	$ 350,000
Interest rate	2.05%
Debt instrument, basis spread on variable rate	0.25%
Debt instrument, redemption price (as percent)	100.00%