Loans Receivable - Reconciliation of Past Due Loans (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due loans	$ 4,019	$ 2,331
Current	879,738	867,399
Total loans	883,757	869,730
Real estate loans
Financing Receivable, Recorded Investment, Aging [Abstract]
Total loans	730,200	767,600
Residential segment
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due loans	1,174	709
Current	693,847	725,137
Total loans	695,021	725,846
Residential segment | Commercial real estate
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due loans	0	0
Current	255,722	253,235
Total loans	255,722	253,235
Residential segment | Construction and land
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due loans	38	80
Current	37,149	54,022
Total loans	37,187	54,102
Consumer
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due loans	2,730	699
Current	144,435	124,287
Total loans	147,165	124,986
Consumer | Home equity
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due loans	323	136
Current	34,723	37,493
Total loans	35,046	37,629
Consumer | Auto and other consumer
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due loans	2,407	563
Current	109,712	86,794
Total loans	112,119	87,357
Commercial business loans
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due loans	115	923
Current	41,456	17,975
Total loans	41,571	18,898
30 to 59 Days Past Due
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due loans	2,688	1,815
30 to 59 Days Past Due | Residential segment
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due loans	966	324
30 to 59 Days Past Due | Residential segment | Commercial real estate
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due loans	0	0
30 to 59 Days Past Due | Residential segment | Construction and land
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due loans	38	35
30 to 59 Days Past Due | Consumer
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due loans	1,722	568
30 to 59 Days Past Due | Consumer | Home equity
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due loans	299	97
30 to 59 Days Past Due | Consumer | Auto and other consumer
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due loans	1,423	471
30 to 59 Days Past Due | Commercial business loans
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due loans	0	923
60 to 89 Days Past Due
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due loans	601	312
60 to 89 Days Past Due | Residential segment
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due loans	92	190
60 to 89 Days Past Due | Residential segment | Commercial real estate
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due loans	0	0
60 to 89 Days Past Due | Residential segment | Construction and land
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due loans	0	14
60 to 89 Days Past Due | Consumer
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due loans	394	122
60 to 89 Days Past Due | Consumer | Home equity
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due loans	24	30
60 to 89 Days Past Due | Consumer | Auto and other consumer
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due loans	370	92
60 to 89 Days Past Due | Commercial business loans
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due loans	115	0
90 Days or More Past Due
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due loans	730	204
90 Days or More Past Due | Residential segment
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due loans	116	195
90 Days or More Past Due | Residential segment | Commercial real estate
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due loans	0	0
90 Days or More Past Due | Residential segment | Construction and land
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due loans	0	31
90 Days or More Past Due | Consumer
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due loans	614	9
90 Days or More Past Due | Consumer | Home equity
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due loans	0	9
90 Days or More Past Due | Consumer | Auto and other consumer
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due loans	614	0
90 Days or More Past Due | Commercial business loans
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due loans	0	0
One- to four-family | Residential segment | Real estate loans
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due loans	1,136	629
Current	304,878	335,549
Total loans	306,014	336,178
One- to four-family | 30 to 59 Days Past Due | Residential segment | Real estate loans
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due loans	928	289
One- to four-family | 60 to 89 Days Past Due | Residential segment | Real estate loans
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due loans	92	176
One- to four-family | 90 Days or More Past Due | Residential segment | Real estate loans
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due loans	116	164
Multi-family | Residential segment | Real estate loans
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due loans	0	0
Current	96,098	82,331
Total loans	96,098	82,331
Multi-family | 30 to 59 Days Past Due | Residential segment | Real estate loans
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due loans	0	0
Multi-family | 60 to 89 Days Past Due | Residential segment | Real estate loans
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due loans	0	0
Multi-family | 90 Days or More Past Due | Residential segment | Real estate loans
Financing Receivable, Recorded Investment, Aging [Abstract]
Past due loans	$ 0	$ 0