Loans Receivable - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual interest income recognized			$ 2,663
Impaired, interest lost on nonaccrual loans			$ 1,624
Percent of TDRs classified as performing			96.30%
Troubled debt restructuring, amount	$ 619	$ 789	$ 982	$ 12,240
Basis point reduction, minimum			1.00%
Basis point reduction, maximum			2.00%
Single family residential loans as percentage of restructured loans	91.50%		91.50%
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			$ 128,858