Loans and allowance for credit losses - Allowance for Credit Losses by Class of Financing Receivable Disaggregated by Measurement Methodology (Details) - USD ($)
$ in Thousands
Dec. 31, 2020
Jan. 01, 2020
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]          
Individually evaluated for credit loss/impairment $ 2,039   $ 895 $ 268  
Collectively evaluated for credit loss/impairment 149,405   28,571 27,783  
Ending balance 170,389 $ 31,139 31,139 28,932 $ 24,041
Purchased Credit Impaired loans          
Accounts, Notes, Loans and Financing Receivable [Line Items]          
Collectively evaluated for credit loss/impairment 18,945   1,673 881  
Commercial and industrial          
Accounts, Notes, Loans and Financing Receivable [Line Items]          
Individually evaluated for credit loss/impairment 373   241 3  
Collectively evaluated for credit loss/impairment 13,493   4,457 5,247  
Ending balance 14,748   4,805 5,348 4,461
Commercial and industrial | Purchased Credit Impaired loans          
Accounts, Notes, Loans and Financing Receivable [Line Items]          
Collectively evaluated for credit loss/impairment 882   107 98  
Construction          
Accounts, Notes, Loans and Financing Receivable [Line Items]          
Individually evaluated for credit loss/impairment 95   0 0  
Collectively evaluated for credit loss/impairment 54,065   10,192 9,677  
Ending balance 58,477   10,194 9,729 7,135
Construction | Purchased Credit Impaired loans          
Accounts, Notes, Loans and Financing Receivable [Line Items]          
Collectively evaluated for credit loss/impairment 4,317   2 52  
Residential real estate | 1-to-4 family mortgage          
Accounts, Notes, Loans and Financing Receivable [Line Items]          
Individually evaluated for credit loss/impairment 0   8 7  
Collectively evaluated for credit loss/impairment 17,206   2,940 3,205  
Ending balance 19,220   3,112 3,428 3,197
Residential real estate | 1-to-4 family mortgage | Purchased Credit Impaired loans          
Accounts, Notes, Loans and Financing Receivable [Line Items]          
Collectively evaluated for credit loss/impairment 2,014   164 216  
Residential real estate | Residential line of credit          
Accounts, Notes, Loans and Financing Receivable [Line Items]          
Individually evaluated for credit loss/impairment 9   9 0  
Collectively evaluated for credit loss/impairment 10,031   743 811  
Ending balance 10,534   752 811 944
Residential real estate | Residential line of credit | Purchased Credit Impaired loans          
Accounts, Notes, Loans and Financing Receivable [Line Items]          
Collectively evaluated for credit loss/impairment 494   0 0  
Residential real estate | Multi-family mortgage          
Accounts, Notes, Loans and Financing Receivable [Line Items]          
Individually evaluated for credit loss/impairment 0   0 0  
Collectively evaluated for credit loss/impairment 6,326   544 566  
Ending balance 7,174   544 566 434
Residential real estate | Multi-family mortgage | Purchased Credit Impaired loans          
Accounts, Notes, Loans and Financing Receivable [Line Items]          
Collectively evaluated for credit loss/impairment 848   0 0  
Commercial real estate | Owner occupied          
Accounts, Notes, Loans and Financing Receivable [Line Items]          
Individually evaluated for credit loss/impairment 30   238 53  
Collectively evaluated for credit loss/impairment 4,062   3,853 3,066  
Ending balance 4,849   4,109 3,132 3,558
Commercial real estate | Owner occupied | Purchased Credit Impaired loans          
Accounts, Notes, Loans and Financing Receivable [Line Items]          
Collectively evaluated for credit loss/impairment 757   18 13  
Commercial real estate | Non-owner occupied          
Accounts, Notes, Loans and Financing Receivable [Line Items]          
Individually evaluated for credit loss/impairment 1,531   399 205  
Collectively evaluated for credit loss/impairment 33,706   3,909 3,628  
Ending balance 44,147   4,621 4,149 2,817
Commercial real estate | Non-owner occupied | Purchased Credit Impaired loans          
Accounts, Notes, Loans and Financing Receivable [Line Items]          
Collectively evaluated for credit loss/impairment 8,910   313 316  
Consumer and other          
Accounts, Notes, Loans and Financing Receivable [Line Items]          
Individually evaluated for credit loss/impairment 1   0 0  
Collectively evaluated for credit loss/impairment 10,516   1,933 1,583  
Ending balance 11,240   3,002 1,769 $ 1,495
Consumer and other | Purchased Credit Impaired loans          
Accounts, Notes, Loans and Financing Receivable [Line Items]          
Collectively evaluated for credit loss/impairment $ 723   $ 1,069 $ 186