Loans Receivable - Financing Receivables, Aging of loans (Details) - USD ($)	Mar. 31, 2021	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans	$ 1,116,391,000	$ 1,117,410,000
Financing Receivable, 90 Days or More Past Due, Still Accruing	0	0
One-to-four family, residential, owner occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	77,000
Current	199,845,000	206,246,000
Total Loans	199,845,000	206,323,000
One to four family residential non owner occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	159,000
Current	179,401,000	175,478,000
Total Loans	179,401,000	175,637,000
Multifamily
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	2,036,000	2,104,000
Current	138,032,000	134,590,000
Total Loans	140,068,000	136,694,000
Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Current	385,470,000	385,265,000
Total Loans	385,470,000	385,265,000
Construction/  Land
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Current	94,545,000	92,207,000
Total Loans	94,545,000	92,207,000
Total real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	2,036,000	2,340,000
Current	997,293,000	993,786,000
Total Loans	999,329,000	996,126,000
Business
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	264,000	275,000
Current	78,030,000	80,388,000
Total Loans	78,294,000	80,663,000
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	37,000	38,000
Current	38,731,000	40,583,000
Total Loans	38,768,000	40,621,000
Property total
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	2,337,000	2,653,000
Current	1,114,054,000	1,114,757,000
Total Loans	1,116,391,000	1,117,410,000
Financial Asset, 30 to 59 Days Past Due | One-to-four family, residential, owner occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	77,000
Financial Asset, 30 to 59 Days Past Due | One to four family residential non owner occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	159,000
Financial Asset, 30 to 59 Days Past Due | Multifamily
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Financial Asset, 30 to 59 Days Past Due | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Financial Asset, 30 to 59 Days Past Due | Construction/  Land
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Financial Asset, 30 to 59 Days Past Due | Total real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	236,000
Financial Asset, 30 to 59 Days Past Due | Business
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	264,000	275,000
Financial Asset, 30 to 59 Days Past Due | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	37,000	38,000
Financial Asset, 30 to 59 Days Past Due | Property total
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	301,000	549,000
Financial Asset, 60 to 89 Days Past Due | One-to-four family, residential, owner occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Financial Asset, 60 to 89 Days Past Due | One to four family residential non owner occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Financial Asset, 60 to 89 Days Past Due | Multifamily
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Financial Asset, 60 to 89 Days Past Due | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Financial Asset, 60 to 89 Days Past Due | Construction/  Land
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Financial Asset, 60 to 89 Days Past Due | Total real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Financial Asset, 60 to 89 Days Past Due | Business
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Financial Asset, 60 to 89 Days Past Due | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Financial Asset, 60 to 89 Days Past Due | Property total
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Financial Asset, Equal to or Greater than 90 Days Past Due | One-to-four family, residential, owner occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Financial Asset, Equal to or Greater than 90 Days Past Due | One to four family residential non owner occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Financial Asset, Equal to or Greater than 90 Days Past Due | Multifamily
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	2,036,000	2,104,000
Financial Asset, Equal to or Greater than 90 Days Past Due | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Financial Asset, Equal to or Greater than 90 Days Past Due | Construction/  Land
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Financial Asset, Equal to or Greater than 90 Days Past Due | Total real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	2,036,000	2,104,000
Financial Asset, Equal to or Greater than 90 Days Past Due | Business
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Financial Asset, Equal to or Greater than 90 Days Past Due | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Financial Asset, Equal to or Greater than 90 Days Past Due | Property total
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	$ 2,036,000	$ 2,104,000