Loans - Summary of loans by past due status (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 0	$ 40
Loans Not Past Due	489,423	467,109
Total Loans	489,423	467,149
30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	40
Greater than 90 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Real Estate | 1 - 4 Family Residential
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Loans Not Past Due	52,569	56,043
Total Loans	52,569	56,043
Real Estate | 1 - 4 Family Residential | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Real Estate | 1 - 4 Family Residential | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Real Estate | 1 - 4 Family Residential | Greater than 90 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Real Estate | Multifamily
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Loans Not Past Due	137,908	136,537
Total Loans	137,908	136,537
Real Estate | Multifamily | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Real Estate | Multifamily | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Real Estate | Multifamily | Greater than 90 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Real Estate | Commercial Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Loans Not Past Due	37,819	33,145
Total Loans	37,819	33,145
Real Estate | Commercial Real Estate | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Real Estate | Commercial Real Estate | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Real Estate | Commercial Real Estate | Greater than 90 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Real Estate | Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Loans Not Past Due	6,337	5,921
Total Loans	6,337	5,921
Real Estate | Construction | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Real Estate | Construction | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Real Estate | Construction | Greater than 90 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Loans Not Past Due	212,600	191,828
Total Loans	212,600	191,828
Commercial | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Commercial | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Commercial | Greater than 90 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	40
Loans Not Past Due	42,190	43,635
Total Loans	42,190	43,675
Consumer | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Consumer | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	40
Consumer | Greater than 90 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 0	$ 0