Loans Receivable and Allowance for Credit Losses - Narrative (Details) - USD ($)	Jun. 30, 2023	Dec. 31, 2022	Sep. 30, 2023	Sep. 30, 2022
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, net of allowance of $15,306, and $15,227		$ 1,167,083,000	$ 1,168,079,000
Recorded Investment		48,521,000	45,850,000
Total loans		1,182,310,000	1,183,385,000
Multifamily
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment			1,601,000
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment			44,249,000
Financial Asset, Equal to or Greater than 90 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total TDR loans		0	0
PPP Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, net			551,000	$ 784,000
Property total
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired financing receivable, related allowance		13,000
Recorded Investment		48,534,000
Total loans			1,183,385,000
Property total | Nonperforming
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans			201,000
Property total | Financial Asset, Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, net of allowance of $15,306, and $15,227		$ 220,000	1,200,000
Percent of total loans receivable	0.10%	0.02%
Total loans			1,238,000
Property total | Financial Asset, Equal to or Greater than 90 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans			201,000
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans			72,148,000
Consumer | Nonperforming
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans			201,000
Consumer | Financial Asset, Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans			881,000
Consumer | Financial Asset, Equal to or Greater than 90 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans		$ 193,000	201,000
One-to-four family residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans			493,208,000
One-to-four family residential | Nonperforming
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans			0
FHLB of Des Moines | Asset Pledged as Collateral
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable		605,000,000	655,700,000
Federal Reserve Bank | Asset Pledged as Collateral
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable		$ 87,700,000	$ 81,100,000