Loans - Summary of loans by past due status (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 326	$ 40
Loans Not Past Due	533,104	467,109
Total Loans	533,430	467,149
30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	326	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	49,214	56,043
Total Loans	49,214	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	136,799	136,537
Total Loans	136,799	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	49,125	33,145
Total Loans	49,125	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	6,450	5,921
Total Loans	6,450	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	247,931	191,828
Total Loans	247,931	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	326	40
Loans Not Past Due	43,585	43,635
Total Loans	43,911	43,675
Consumer | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	326	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