Income Taxes - Reconciliation Between Federal Statutory Income Tax Rate and Effective Tax Rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Income Tax Disclosure [Abstract]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	21.00%
Income tax provision at U.S. federal statutory rate	$ 134,825	$ 116,261	$ 98,975
State income taxes, net of U.S. federal benefit	13,109	14,135	8,359
Foreign tax rate differential	6,675	9,489	3,058
Research credits	(5,472)	(3,600)	(5,932)
Valuation allowance	(2,183)	(14,451)	(11,768)
Excess tax benefits relating to share-based compensation	(14,907)	(949)	702
GILTI, FDII, BEAT and FTC	(9,265)	(9,010)	(2,491)
Effective Income Tax Rate Reconciliation, Other Adjustments, Amount	6,432	12,374	6,865
Total provision	$ 129,214	$ 124,249	$ 97,768