Loans - Summary of loans by credit quality indicator based on internally assigned credit grade (Details) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2019 USD ($) item	Sep. 30, 2018 item	Dec. 31, 2018 USD ($) item
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 533,430		$ 467,149
Number of loans identified as troubled debt restructuring | item	0		0
Number of loans modified | item	0	0
Pass
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 527,943		$ 457,803
Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total Loans	4,271		9,166
Substandard
Financing Receivable, Recorded Investment [Line Items]
Total Loans	1,216		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	49,214		56,043
Real Estate | 1 - 4 Family Residential | Pass
Financing Receivable, Recorded Investment [Line Items]
Total Loans	49,214		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	136,799		136,537
Real Estate | Multifamily | Pass
Financing Receivable, Recorded Investment [Line Items]
Total Loans	136,799		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	49,125		33,145
Real Estate | Commercial Real Estate | Pass
Financing Receivable, Recorded Investment [Line Items]
Total Loans	49,125		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	247,931		191,828
Commercial | Pass
Financing Receivable, Recorded Investment [Line Items]
Total Loans	243,520		182,482
Commercial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total Loans	4,271		9,166
Commercial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total Loans	140		180
Commercial | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total Loans	0		0
Consumer
Financing Receivable, Recorded Investment [Line Items]
Total Loans	43,911		43,675
Consumer | Pass
Financing Receivable, Recorded Investment [Line Items]
Total Loans	42,835		43,675
Consumer | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total Loans	0		0
Consumer | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total Loans	1,076		0
Consumer | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 0		$ 0