Income Taxes - Schedule of Unrecognized Tax Benefit (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Reconciliation Of Unrecognized Tax Benefits Excluding Amounts Pertaining To Examined Tax Returns Roll Forward
Unrecognized tax benefit, beginning of year	$ 11,484	$ 9,812	$ 14,752
Tax positions related to current year:
Additions	2,173	1,466	1,456
Tax positions related to prior years:
Additions	2,452	1,375	0
Reductions	(2)	(9)	(4,631)
Settlements	0	(1,160)	0
Statute expirations	0	0	(1,765)
Unrecognized tax benefit, end of year	$ 16,107	$ 11,484	$ 9,812