Loans and allowance for credit losses - Changes in Allowance for Credit Losses by Class of Financing Receivable (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Allowance for Loan and Lease Losses [Roll Forward]      
Balance at beginning of period $ 31,139 $ 28,932 $ 24,041
Provision for credit losses 94,606 7,053 5,398
Recoveries of loans previously charged-off 3,003 1,106 2,647
Loans charged off (15,305) (5,952) (2,805)
Initial allowance on loans purchased with deteriorated credit quality 25,500    
Adjustments for transfers to loans HFS     (349)
Balance at end of period 170,389 31,139 28,932
Non-purchased credit deteriorated loans | Cumulative effect of change in accounting principle      
Allowance for Loan and Lease Losses [Roll Forward]      
Balance at beginning of period 30,888    
Balance at end of period   30,888  
Purchased Credit Impaired loans | Cumulative effect of change in accounting principle      
Allowance for Loan and Lease Losses [Roll Forward]      
Balance at beginning of period 558    
Balance at end of period   558  
Commercial and industrial      
Allowance for Loan and Lease Losses [Roll Forward]      
Balance at beginning of period 4,805 5,348 4,461
Provision for credit losses 13,830 2,251 1,395
Recoveries of loans previously charged-off 1,712 136 390
Loans charged off (11,735) (2,930) (898)
Initial allowance on loans purchased with deteriorated credit quality 754    
Adjustments for transfers to loans HFS     0
Balance at end of period 14,748 4,805 5,348
Commercial and industrial | Non-purchased credit deteriorated loans | Cumulative effect of change in accounting principle      
Allowance for Loan and Lease Losses [Roll Forward]      
Balance at beginning of period 5,300    
Balance at end of period   5,300  
Commercial and industrial | Purchased Credit Impaired loans | Cumulative effect of change in accounting principle      
Allowance for Loan and Lease Losses [Roll Forward]      
Balance at beginning of period 82    
Balance at end of period   82  
Construction      
Allowance for Loan and Lease Losses [Roll Forward]      
Balance at beginning of period 10,194 9,729 7,135
Provision for credit losses 40,807 454 1,459
Recoveries of loans previously charged-off 205 11 1,164
Loans charged off (18) 0 (29)
Initial allowance on loans purchased with deteriorated credit quality 5,606    
Adjustments for transfers to loans HFS     0
Balance at end of period 58,477 10,194 9,729
Construction | Non-purchased credit deteriorated loans | Cumulative effect of change in accounting principle      
Allowance for Loan and Lease Losses [Roll Forward]      
Balance at beginning of period 1,533    
Balance at end of period   1,533  
Construction | Purchased Credit Impaired loans | Cumulative effect of change in accounting principle      
Allowance for Loan and Lease Losses [Roll Forward]      
Balance at beginning of period 150    
Balance at end of period   150  
Residential real estate | 1-to-4 family mortgage      
Allowance for Loan and Lease Losses [Roll Forward]      
Balance at beginning of period 3,112 3,428 3,197
Provision for credit losses 6,408 (175) 547
Recoveries of loans previously charged-off 122 79 171
Loans charged off (403) (220) (138)
Initial allowance on loans purchased with deteriorated credit quality 1,640    
Adjustments for transfers to loans HFS     (349)
Balance at end of period 19,220 3,112 3,428
Residential real estate | 1-to-4 family mortgage | Non-purchased credit deteriorated loans | Cumulative effect of change in accounting principle      
Allowance for Loan and Lease Losses [Roll Forward]      
Balance at beginning of period 7,920    
Balance at end of period   7,920  
Residential real estate | 1-to-4 family mortgage | Purchased Credit Impaired loans | Cumulative effect of change in accounting principle      
Allowance for Loan and Lease Losses [Roll Forward]      
Balance at beginning of period 421    
Balance at end of period   421  
Residential real estate | Residential line of credit      
Allowance for Loan and Lease Losses [Roll Forward]      
Balance at beginning of period 752 811 944
Provision for credit losses 5,649 112 (275)
Recoveries of loans previously charged-off 125 138 178
Loans charged off (22) (309) (36)
Initial allowance on loans purchased with deteriorated credit quality 572    
Adjustments for transfers to loans HFS     0
Balance at end of period 10,534 752 811
Residential real estate | Residential line of credit | Non-purchased credit deteriorated loans | Cumulative effect of change in accounting principle      
Allowance for Loan and Lease Losses [Roll Forward]      
Balance at beginning of period 3,461    
Balance at end of period   3,461  
Residential real estate | Residential line of credit | Purchased Credit Impaired loans | Cumulative effect of change in accounting principle      
Allowance for Loan and Lease Losses [Roll Forward]      
Balance at beginning of period (3)    
Balance at end of period   (3)  
Residential real estate | Multi-family mortgage      
Allowance for Loan and Lease Losses [Roll Forward]      
Balance at beginning of period 544 566 434
Provision for credit losses 5,506 (22) 132
Recoveries of loans previously charged-off 0 0 0
Loans charged off 0 0 0
Initial allowance on loans purchased with deteriorated credit quality 784    
Adjustments for transfers to loans HFS     0
Balance at end of period 7,174 544 566
Residential real estate | Multi-family mortgage | Non-purchased credit deteriorated loans | Cumulative effect of change in accounting principle      
Allowance for Loan and Lease Losses [Roll Forward]      
Balance at beginning of period 340    
Balance at end of period   340  
Residential real estate | Multi-family mortgage | Purchased Credit Impaired loans | Cumulative effect of change in accounting principle      
Allowance for Loan and Lease Losses [Roll Forward]      
Balance at beginning of period 0    
Balance at end of period   0  
Commercial real estate | Owner occupied      
Allowance for Loan and Lease Losses [Roll Forward]      
Balance at beginning of period 4,109 3,132 3,558
Provision for credit losses (1,739) 869 (478)
Recoveries of loans previously charged-off 83 108 143
Loans charged off (304) 0 (91)
Initial allowance on loans purchased with deteriorated credit quality 659    
Adjustments for transfers to loans HFS     0
Balance at end of period 4,849 4,109 3,132
Commercial real estate | Owner occupied | Non-purchased credit deteriorated loans | Cumulative effect of change in accounting principle      
Allowance for Loan and Lease Losses [Roll Forward]      
Balance at beginning of period 1,879    
Balance at end of period   1,879  
Commercial real estate | Owner occupied | Purchased Credit Impaired loans | Cumulative effect of change in accounting principle      
Allowance for Loan and Lease Losses [Roll Forward]      
Balance at beginning of period 162    
Balance at end of period   162  
Commercial real estate | Non-owner occupied      
Allowance for Loan and Lease Losses [Roll Forward]      
Balance at beginning of period 4,621 4,149 2,817
Provision for credit losses 17,789 484 1,281
Recoveries of loans previously charged-off 0 0 51
Loans charged off (711) (12) 0
Initial allowance on loans purchased with deteriorated credit quality 15,442    
Adjustments for transfers to loans HFS     0
Balance at end of period 44,147 4,621 4,149
Commercial real estate | Non-owner occupied | Non-purchased credit deteriorated loans | Cumulative effect of change in accounting principle      
Allowance for Loan and Lease Losses [Roll Forward]      
Balance at beginning of period 6,822    
Balance at end of period   6,822  
Commercial real estate | Non-owner occupied | Purchased Credit Impaired loans | Cumulative effect of change in accounting principle      
Allowance for Loan and Lease Losses [Roll Forward]      
Balance at beginning of period 184    
Balance at end of period   184  
Consumer and other      
Allowance for Loan and Lease Losses [Roll Forward]      
Balance at beginning of period 3,002 1,769 1,495
Provision for credit losses 6,356 3,080 1,337
Recoveries of loans previously charged-off 756 634 550
Loans charged off (2,112) (2,481) (1,613)
Initial allowance on loans purchased with deteriorated credit quality 43    
Adjustments for transfers to loans HFS     0
Balance at end of period 11,240 3,002 $ 1,769
Consumer and other | Non-purchased credit deteriorated loans | Cumulative effect of change in accounting principle      
Allowance for Loan and Lease Losses [Roll Forward]      
Balance at beginning of period 3,633    
Balance at end of period   3,633  
Consumer and other | Purchased Credit Impaired loans | Cumulative effect of change in accounting principle      
Allowance for Loan and Lease Losses [Roll Forward]      
Balance at beginning of period $ (438)    
Balance at end of period   $ (438)