Loans - Summary of loans by credit quality indicator based on internally assigned credit grade (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 467,149	$ 348,089
Pass
Financing Receivable, Recorded Investment [Line Items]
Total Loans	457,803	338,254
Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total Loans	9,166	9,835
Substandard
Financing Receivable, Recorded Investment [Line Items]
Total Loans	180	0
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	56,043	51,556
Real Estate | 1 - 4 Family Residential | Pass
Financing Receivable, Recorded Investment [Line Items]
Total Loans	56,043	51,556
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	136,537	98,432
Real Estate | Multifamily | Pass
Financing Receivable, Recorded Investment [Line Items]
Total Loans	136,537	98,432
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	33,145	24,761
Real Estate | Commercial Real Estate | Pass
Financing Receivable, Recorded Investment [Line Items]
Total Loans	33,145	24,761
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	5,921	5,047
Real Estate | Construction | Pass
Financing Receivable, Recorded Investment [Line Items]
Total Loans	5,921	5,047
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	191,828	136,412
Commercial | Pass
Financing Receivable, Recorded Investment [Line Items]
Total Loans	182,482	126,577
Commercial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total Loans	9,166	9,835
Commercial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total Loans	180	0
Commercial | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total Loans	0	0
Consumer
Financing Receivable, Recorded Investment [Line Items]
Total Loans	43,675	31,881
Consumer | Pass
Financing Receivable, Recorded Investment [Line Items]
Total Loans	43,675	31,881
Consumer | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total Loans	0	0
Consumer | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total Loans	0	0
Consumer | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 0	$ 0