Loans Receivable - Narrative (Details) $ in Thousands	3 Months Ended
	Dec. 31, 2022 USD ($) portfolioSegment	Sep. 30, 2022 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of portfolio segments for loans held for investment | portfolioSegment	2
Accrued interest receivables for loans	$ 67,169	$ 57,070
Loans pledged to secure borrowings from the Federal Home Loan Bank	8,636,895	$ 8,224,951
Nonaccrual interest income recognized	534
Impaired, interest income on accrual accrual and performed loans	$ 358
Basis point reduction, minimum	1.00%
Basis point reduction, maximum	2.00%
Percent of TDRs classified as performing	98.00%
Single family residential loans as percentage of restructured loans	82.50%
Performing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Troubled debt restructuring, amount	$ 55,515
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