Customer Accounts - Schedule of Deposits (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Deposit Account Balance
Non-interest checking	$ 2,706,448	$ 3,266,734
Interest checking	3,882,715	3,497,795
Savings	817,547	1,059,093
Money market	3,358,603	4,867,905
Time deposits	5,305,016	3,338,043
Customer accounts	$ 16,070,329	$ 16,029,570
As a % of Total Deposits
Non-interest checking	16.80%	20.40%
Interest checking	24.20%	21.80%
Savings	5.10%	6.60%
Money market	20.90%	30.40%
Time deposits	33.00%	20.80%
Total	100.00%	100.00%
Weighted Average Rate
Interest checking	2.28%	0.90%
Savings	0.21%	0.13%
Money market	1.48%	0.49%
Time deposits	3.77%	0.74%
Total	2.12%	0.51%	0.23%