Loans - Summary of loans by credit quality indicator based on internally assigned credit grade (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 564,979	$ 467,149	$ 467,149
Pass
Financing Receivable, Recorded Investment [Line Items]
Total Loans	559,963	457,803
Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total Loans	3,415	9,166
Substandard
Financing Receivable, Recorded Investment [Line Items]
Total Loans	1,601	180
Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total Loans	0	0
Real Estate | 1 - 4 Family Residential
Financing Receivable, Recorded Investment [Line Items]
Total Loans	48,140	56,043
Real Estate | 1 - 4 Family Residential | Pass
Financing Receivable, Recorded Investment [Line Items]
Total Loans	48,140	56,043
Real Estate | 1 - 4 Family Residential | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total Loans	0	0
Real Estate | 1 - 4 Family Residential | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total Loans	0	0
Real Estate | 1 - 4 Family Residential | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total Loans	0	0
Real Estate | Multifamily
Financing Receivable, Recorded Investment [Line Items]
Total Loans	152,633	136,537
Real Estate | Multifamily | Pass
Financing Receivable, Recorded Investment [Line Items]
Total Loans	152,633	136,537
Real Estate | Multifamily | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total Loans	0	0
Real Estate | Multifamily | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total Loans	0	0
Real Estate | Multifamily | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total Loans	0	0
Real Estate | Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans	52,477	33,145
Real Estate | Commercial Real Estate | Pass
Financing Receivable, Recorded Investment [Line Items]
Total Loans	52,477	33,145
Real Estate | Commercial Real Estate | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total Loans	0	0
Real Estate | Commercial Real Estate | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total Loans	0	0
Real Estate | Commercial Real Estate | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total Loans	0	0
Real Estate | Construction
Financing Receivable, Recorded Investment [Line Items]
Total Loans	6,450	5,921
Real Estate | Construction | Pass
Financing Receivable, Recorded Investment [Line Items]
Total Loans	6,450	5,921
Real Estate | Construction | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total Loans	0	0
Real Estate | Construction | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total Loans	0	0
Real Estate | Construction | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total Loans	0	0
Commercial
Financing Receivable, Recorded Investment [Line Items]
Total Loans	257,957	191,828
Commercial | Pass
Financing Receivable, Recorded Investment [Line Items]
Total Loans	257,832	182,482
Commercial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total Loans	0	9,166
Commercial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total Loans	125	180
Commercial | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total Loans	0	0
Consumer
Financing Receivable, Recorded Investment [Line Items]
Total Loans	47,322	43,675
Consumer | Pass
Financing Receivable, Recorded Investment [Line Items]
Total Loans	42,431	43,675
Consumer | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total Loans	3,415	0
Consumer | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total Loans	1,476	0
Consumer | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 0	$ 0