Income Taxes - Income Before Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Income Tax Disclosure [Abstract]
Domestic	$ 1,418,457	$ 1,351,696	$ 1,495,899
Foreign	742,379	831,361	725,960
Income before income taxes	$ 2,160,836	$ 2,183,057	$ 2,221,859