Borrowings - 2026 Notes (Narrative) (Details) - USD ($) $ in Thousands	Feb. 24, 2021	Sep. 30, 2025	Sep. 30, 2024	Oct. 13, 2021
Debt Instrument [Line Items]
Long-term debt		$ 4,900,773	$ 4,599,430
2026 Notes
Debt Instrument [Line Items]
Debt instrument, face amount	$ 400,000			$ 200,000
Long-term debt		$ 600,000	$ 600,000
Interest rate	2.50%
Debt instrument, basis spread on variable rate	0.30%
Debt instrument, redemption price (as percent)	100.00%