Loans - Credit Quality Indicators (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	$ 692,749	$ 621,907
Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	575,057	593,823
Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	89,570	3,353
Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	14,913	9,988
Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	13,209	14,743
Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	0	0
Loss
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	0	0
Real estate loans:
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	506,125	510,262
Consumer loans:
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	75,599	72,714
Commercial business
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	111,025	38,931
Commercial business | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	102,864	35,347
Commercial business | Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	5,859	378
Commercial business | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	395	1,649
Commercial business | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	1,907	1,557
Commercial business | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	0	0
Commercial business | Loss
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	0	0
One-to-four family | Real estate loans:
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	140,356	149,393
One-to-four family | Real estate loans: | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	120,789	138,900
One-to-four family | Real estate loans: | Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	15,100	0
One-to-four family | Real estate loans: | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	0	2,484
One-to-four family | Real estate loans: | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	4,467	8,009
One-to-four family | Real estate loans: | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	0	0
One-to-four family | Real estate loans: | Loss
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	0	0
Home equity | Real estate loans:
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	17,727	23,845
Home equity | Real estate loans: | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	16,906	23,206
Home equity | Real estate loans: | Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	269	0
Home equity | Real estate loans: | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	0	0
Home equity | Real estate loans: | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	552	639
Home equity | Real estate loans: | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	0	0
Home equity | Real estate loans: | Loss
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	0	0
Commercial and multifamily | Real estate loans:
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	275,876	261,268
Commercial and multifamily | Real estate loans: | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	235,013	256,139
Commercial and multifamily | Real estate loans: | Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	25,147	217
Commercial and multifamily | Real estate loans: | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	10,852	2,178
Commercial and multifamily | Real estate loans: | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	4,864	2,734
Commercial and multifamily | Real estate loans: | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	0	0
Commercial and multifamily | Real estate loans: | Loss
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	0	0
Construction and land | Real estate loans:
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	72,166	75,756
Construction and land | Real estate loans: | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	25,748	68,268
Construction and land | Real estate loans: | Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	42,149	2,634
Construction and land | Real estate loans: | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	3,666	3,677
Construction and land | Real estate loans: | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	603	1,177
Construction and land | Real estate loans: | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	0	0
Construction and land | Real estate loans: | Loss
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	0	0
Manufactured homes | Consumer loans:
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	20,948	20,613
Manufactured homes | Consumer loans: | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	19,670	20,204
Manufactured homes | Consumer loans: | Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	1,033	124
Manufactured homes | Consumer loans: | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	0	0
Manufactured homes | Consumer loans: | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	245	285
Manufactured homes | Consumer loans: | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	0	0
Manufactured homes | Consumer loans: | Loss
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	0	0
Floating homes | Consumer loans:
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	42,399	43,799
Floating homes | Consumer loans: | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	41,870	43,509
Floating homes | Consumer loans: | Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	0	0
Floating homes | Consumer loans: | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	0	0
Floating homes | Consumer loans: | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	529	290
Floating homes | Consumer loans: | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	0	0
Floating homes | Consumer loans: | Loss
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	0	0
Other consumer | Consumer loans:
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	12,252	8,302
Other consumer | Consumer loans: | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	12,197	8,250
Other consumer | Consumer loans: | Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	13	0
Other consumer | Consumer loans: | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	0	0
Other consumer | Consumer loans: | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	42	52
Other consumer | Consumer loans: | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	0	0
Other consumer | Consumer loans: | Loss
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held-for-portfolio	$ 0	$ 0