Loans Receivable - Additional Information (Details) - USD ($) $ in Thousands	9 Months Ended
	Jun. 30, 2022	Sep. 30, 2021
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrued interest receivables for loans	$ 49,263	$ 46,234
Loans pledged to secure borrowings from the Federal Home Loan Bank	7,841,568	$ 5,930,015
Nonaccrual interest income recognized	2,544
Impaired, interest income on accrual accrual and performed loans	$ 969
Basis point reduction, minimum	1.00%
Basis point reduction, maximum	2.00%
Percent of TDRs classified as performing	97.60%
Single family residential loans as percentage of restructured loans	82.70%
Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term for payment and rate reduction	6 months
Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term for payment and rate reduction	24 months
Performing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Troubled debt restructuring, amount	$ 58,896