Loans and allowance for loan losses - Information on nonaccrual loans (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Recorded Investment, Nonaccrual Status	$ 1,317	$ 1,868
Commercial Real Estate [Member] | Home equity lines [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Recorded Investment, Nonaccrual Status	300	300
Commercial Real Estate Non-Owner Occupied [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Recorded Investment, Nonaccrual Status		497
Owner Occupied [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Recorded Investment, Nonaccrual Status		497
Consumer Real Estate Secured By 1-4 Family Residential [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Recorded Investment, Nonaccrual Status	1,107	1,205
First Deed of Trust [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Recorded Investment, Nonaccrual Status	745	842
Second Deed of Trust [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Recorded Investment, Nonaccrual Status	62	63
Commercial and industrial loans (except those secured by real estate)
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Recorded Investment, Nonaccrual Status	$ 210	$ 166