Income Taxes - Schedule of Unrecognized Tax Benefit (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefit, beginning of year	$ 23,923	$ 21,166	$ 16,107
Tax positions related to current year:
Additions	7,075	3,144	4,844
Tax positions related to prior years:
Additions	20,855	785	30,130
Reductions	0	(1,172)	(478)
Settlements	0	0	(29,437)
Statute expirations	(1,111)	0	0
Unrecognized tax benefit, end of year	$ 50,742	$ 23,923	$ 21,166