Loans Receivable - Credit Quality Indicators by Class of Loan (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	$ 883,757	$ 869,730
Recorded investment, nonaccrual loans	1,796	1,723
Nonperforming
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,796	1,723
Performing
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	881,961	868,007
Real estate loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	730,200	767,600
Residential segment
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	695,021	725,846
Residential segment | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	255,722	253,235
Residential segment | Commercial real estate | Nonperforming
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	109	133
Recorded investment, nonaccrual loans	109	133
Residential segment | Commercial real estate | Performing
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	255,613	253,102
Residential segment | Construction and land
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	37,187	54,102
Residential segment | Construction and land | Nonperforming
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	29	44
Recorded investment, nonaccrual loans	29	44
Residential segment | Construction and land | Performing
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	37,158	54,058
Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	147,165	124,986
Consumer | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	35,046	37,629
Consumer | Home equity | Nonperforming
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	112	369
Recorded investment, nonaccrual loans	112	369
Consumer | Home equity | Performing
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	34,934	37,260
Consumer | Auto and other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	112,119	87,357
Consumer | Auto and other consumer | Nonperforming
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	848	245
Recorded investment, nonaccrual loans	848	245
Consumer | Auto and other consumer | Performing
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	111,271	87,112
Consumer | Commercial business loans | Nonperforming
Financing Receivable, Credit Quality Indicator [Line Items]
Recorded investment, nonaccrual loans	0	173
Commercial business loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	41,571	18,898
Commercial business loans | Nonperforming
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	173
Commercial business loans | Performing
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	41,571	18,725
Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	865,674	847,754
Pass | Residential segment
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	684,434	709,096
Pass | Residential segment | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	251,531	244,919
Pass | Residential segment | Construction and land
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	35,897	51,480
Pass | Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	141,587	122,138
Pass | Consumer | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	34,260	36,559
Pass | Consumer | Auto and other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	107,327	85,579
Pass | Commercial business loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	39,653	16,520
Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	8,055	16,134
Watch | Residential segment
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	3,966	12,626
Watch | Residential segment | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	97	6,281
Watch | Residential segment | Construction and land
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,184	2,578
Watch | Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	3,713	1,775
Watch | Consumer | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	470	465
Watch | Consumer | Auto and other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	3,243	1,310
Watch | Commercial business loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	376	1,733
Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	5,078	2,476
Special Mention | Residential segment
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	4,132	1,730
Special Mention | Residential segment | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	2,800	663
Special Mention | Residential segment | Construction and land
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	77	0
Special Mention | Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	683	274
Special Mention | Consumer | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	89	123
Special Mention | Consumer | Auto and other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	594	151
Special Mention | Commercial business loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	263	472
Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	4,950	3,366
Substandard | Residential segment
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	2,489	2,394
Substandard | Residential segment | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,294	1,372
Substandard | Residential segment | Construction and land
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	29	44
Substandard | Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,182	799
Substandard | Consumer | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	227	482
Substandard | Consumer | Auto and other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	955	317
Substandard | Commercial business loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,279	173
One- to four-family | Residential segment | Real estate loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	306,014	336,178
One- to four-family | Residential segment | Real estate loans | Nonperforming
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	698	759
Recorded investment, nonaccrual loans	698	759
One- to four-family | Residential segment | Real estate loans | Performing
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	305,316	335,419
One- to four-family | Pass | Residential segment | Real estate loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	301,312	330,476
One- to four-family | Watch | Residential segment | Real estate loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	2,685	3,767
One- to four-family | Special Mention | Residential segment | Real estate loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,148	957
One- to four-family | Substandard | Residential segment | Real estate loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	869	978
Multi-family | Residential segment | Real estate loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	96,098	82,331
Multi-family | Residential segment | Real estate loans | Nonperforming
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Multi-family | Residential segment | Real estate loans | Performing
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	96,098	82,331
Multi-family | Pass | Residential segment | Real estate loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	95,694	82,221
Multi-family | Watch | Residential segment | Real estate loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Multi-family | Special Mention | Residential segment | Real estate loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	107	110
Multi-family | Substandard | Residential segment | Real estate loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	$ 297	$ 0