Loans - Composition of Loans (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held-for-portfolio	$ 692,749		$ 621,907
Deferred fees, net	(3,315)		(2,020)
Loans held-for-portfolio	689,434		619,887
Allowance for loan losses	(5,988)	$ (6,031)	(5,640)	$ (5,618)	$ (5,370)	$ (5,774)
Total loans held-for-portfolio, net	683,446		614,247
CARES Act, PPP Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held-for-portfolio	74,800
Real estate loans:
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held-for-portfolio	506,125		510,262
Consumer loans:
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held-for-portfolio	75,599		72,714
Commercial business loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held-for-portfolio	111,025		38,931
Allowance for loan losses	(263)	(501)	(331)	(319)	(509)	(356)
Commercial business loans | CARES Act, PPP Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held-for-portfolio	37,400
One-to-four family | Real estate loans:
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held-for-portfolio	140,356		149,393
Allowance for loan losses	(1,170)	(1,149)	(1,120)	(1,165)	(1,139)	(1,314)
One-to-four family | Real estate loans: | CARES Act, PPP Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held-for-portfolio	16,300
Home equity | Real estate loans:
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held-for-portfolio	17,727		23,845
Allowance for loan losses	(142)	(154)	(178)	(177)	(165)	(202)
Commercial and multifamily | Real estate loans:
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held-for-portfolio	275,876		261,268
Allowance for loan losses	(2,007)	(1,991)	(1,696)	(1,653)	(1,467)	(1,638)
Construction and land | Real estate loans:
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held-for-portfolio	72,166		75,756
Allowance for loan losses	(580)	(623)	(492)	(499)	(464)	(431)
Manufactured homes | Consumer loans:
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held-for-portfolio	20,948		20,613
Allowance for loan losses	(330)	(362)	(480)	(495)	(463)	(427)
Floating homes | Consumer loans:
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held-for-portfolio	42,399		43,799
Allowance for loan losses	(293)	(324)	(283)	(263)	(262)	(265)
Other consumer | Consumer loans:
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held-for-portfolio	12,252		8,302
Allowance for loan losses	$ (115)	$ (127)	$ (112)	$ (110)	$ (120)	$ (112)