Customer Accounts - Interest Expense on Customer Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Banking and Thrift, Interest [Abstract]
Checking accounts	$ 70,396	$ 10,086	$ 5,545
Savings accounts	1,715	1,377	1,143
Money market accounts	47,485	12,423	8,723
Time deposit accounts	119,255	19,422	27,100
Interest expense on customer accounts, gross	238,851	43,308	42,511
Less early withdrawal penalties	(1,618)	(267)	(198)
Interest expense on customer accounts, net	$ 237,233	$ 43,041	$ 42,313
Weighted average interest rate at end of year	2.12%	0.51%	0.23%
Daily weighted average interest rate during the year	1.84%	0.34%	0.35%