Loans and allowance for credit losses - Individually Assessed Allowance (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Jan. 01, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	$ 89,141	$ 31,139	$ 31,139	$ 29,814	$ 28,932
Individually assessed allowance for credit loss	131
Commercial and industrial
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	10,881		4,805	5,514	5,348
Individually assessed allowance for credit loss	0
Construction
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	22,842		10,194	9,758	9,729
Individually assessed allowance for credit loss	0
Residential real estate: | 1-to-4 family mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	13,006		3,112	3,295	3,428
Individually assessed allowance for credit loss	0
Residential real estate: | Residential line of credit
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	6,213		752	731	811
Individually assessed allowance for credit loss	9
Residential real estate: | Multi-family mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	2,328		544	539	566
Individually assessed allowance for credit loss	0
Commercial real estate: | Owner occupied
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	9,047		4,109	3,098	3,132
Individually assessed allowance for credit loss	41
Commercial real estate: | Non-owner occupied
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	18,005		4,621	4,583	4,149
Individually assessed allowance for credit loss	81
Consumer and other
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	6,819		$ 3,002	$ 2,296	$ 1,769
Individually assessed allowance for credit loss	0
Real Estate
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	3,580
Real Estate | Commercial and industrial
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	0
Real Estate | Construction
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	0
Real Estate | Residential real estate: | 1-to-4 family mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	125
Real Estate | Residential real estate: | Residential line of credit
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	320
Real Estate | Residential real estate: | Multi-family mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	0
Real Estate | Commercial real estate: | Owner occupied
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	744
Real Estate | Commercial real estate: | Non-owner occupied
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	2,391
Real Estate | Consumer and other
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	0
Land
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	1,024
Land | Commercial and industrial
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	0
Land | Construction
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	1,024
Land | Residential real estate: | 1-to-4 family mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	0
Land | Residential real estate: | Residential line of credit
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	0
Land | Residential real estate: | Multi-family mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	0
Land | Commercial real estate: | Owner occupied
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	0
Land | Commercial real estate: | Non-owner occupied
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	0
Land | Consumer and other
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	0
Farmland
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	332
Farmland | Commercial and industrial
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	0
Farmland | Construction
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	0
Farmland | Residential real estate: | 1-to-4 family mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	0
Farmland | Residential real estate: | Residential line of credit
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	0
Farmland | Residential real estate: | Multi-family mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	0
Farmland | Commercial real estate: | Owner occupied
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	0
Farmland | Commercial real estate: | Non-owner occupied
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	0
Farmland | Consumer and other
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	332
Equipment
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	36
Equipment | Commercial and industrial
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	36
Equipment | Construction
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	0
Equipment | Residential real estate: | 1-to-4 family mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	0
Equipment | Residential real estate: | Residential line of credit
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	0
Equipment | Residential real estate: | Multi-family mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	0
Equipment | Commercial real estate: | Owner occupied
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	0
Equipment | Commercial real estate: | Non-owner occupied
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	0
Equipment | Consumer and other
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	$ 0