Borrowings - 2027 Notes (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Feb. 15, 2022	Aug. 03, 2021
Debt Instrument [Line Items]
Debt	$ 3,133,332	$ 3,093,603
US Treasury (UST) Interest Rate
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	0.25%
2027 Notes
Debt Instrument [Line Items]
Debt instrument, face amount				$ 350,000
Debt	$ 347,526	$ 350,000
Interest rate			2.05%
Debt instrument, redemption price, percentage	100.00%