Fair value - Carrying amounts and estimated fair value of the company's (Details) - USD ($)
$ in Thousands
Sep. 30, 2020
Dec. 31, 2019
Financial assets    
Investment securities available for sale $ 36,305 $ 46,937
Loans held for sale 27,525 12,722
Fair Value, Inputs, Level 1 [Member] | Reported Value Measurement [Member]    
Financial assets    
Cash 19,605 19,967
Fair Value, Inputs, Level 1 [Member] | Estimate of Fair Value Measurement [Member]    
Financial assets    
Cash 19,605 19,967
Fair Value, Inputs, Level 2 [Member] | Reported Value Measurement [Member]    
Financial assets    
Cash equivalents 18,482  
Investment securities available for sale 36,055 46,687
Federal Home Loan Bank stock 2,141 1,694
Loans held for sale 27,525 12,722
Accrued interest receivable 4,880 2,597
Forward sales commitment 64  
Financial liabilities    
Deposits 573,852 443,208
FHLB borrowings 39,000 29,000
Trust preferred securities 8,764 8,764
Other borrowings 50,740 10,912
Accrued interest payable 231 221
Interest rate lock commitments 40  
Fair Value, Inputs, Level 2 [Member] | Estimate of Fair Value Measurement [Member]    
Financial assets    
Cash equivalents 18,482  
Investment securities available for sale 36,055 46,687
Federal Home Loan Bank stock 2,141 1,694
Loans held for sale 27,525 12,722
Accrued interest receivable 4,880 2,597
Forward sales commitment 64  
Financial liabilities    
Deposits 578,425 443,645
FHLB borrowings 39,447 29,285
Trust preferred securities 9,630 9,812
Other borrowings 50,740 10,912
Accrued interest payable 231 221
Interest rate lock commitments 40  
Fair Value, Inputs, Level 3 [Member] | Reported Value Measurement [Member]    
Financial assets    
Investment securities available for sale 250 250
Loans 598,721 427,827
Impaired loans 1,368 1,468
Assets held for sale 0 514
Other real estate owned 336 526
Bank owned life insurance 7,756 7,612
Fair Value, Inputs, Level 3 [Member] | Estimate of Fair Value Measurement [Member]    
Financial assets    
Investment securities available for sale 250 250
Loans 599,223 429,254
Impaired loans 1,368 1,468
Assets held for sale 0 514
Other real estate owned 336 526
Bank owned life insurance $ 7,756 $ 7,612