Loans and allowance for credit losses - Individually Assessed Allowance for Credit Losses for Collateral Dependent Loans (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Allowance for Credit Loss [Line Items]
Type of Collateral	$ 157,954	$ 170,389	$ 89,141	$ 31,139
Individually assessed allowance for credit loss	1,223	2,039
Commercial and industrial
Financing Receivable, Allowance for Credit Loss [Line Items]
Type of Collateral	14,643	14,748	10,881	4,805
Individually assessed allowance for credit loss	354	373
Construction
Financing Receivable, Allowance for Credit Loss [Line Items]
Type of Collateral	38,622	58,477	22,842	10,194
Individually assessed allowance for credit loss	96	95
Residential real estate | 1-to-4 family mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
Type of Collateral	19,572	19,220	13,006	3,112
Individually assessed allowance for credit loss	0	0
Residential real estate | Residential line of credit
Financing Receivable, Allowance for Credit Loss [Line Items]
Type of Collateral	9,268	10,534	6,213	752
Individually assessed allowance for credit loss	8	9
Residential real estate | Multi-family mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
Type of Collateral	11,657	7,174	2,328	544
Individually assessed allowance for credit loss	0	0
Commercial real estate | Owner occupied
Financing Receivable, Allowance for Credit Loss [Line Items]
Type of Collateral	3,609	4,849	9,047	4,109
Individually assessed allowance for credit loss	70	30
Commercial real estate | Non-owner occupied
Financing Receivable, Allowance for Credit Loss [Line Items]
Type of Collateral	50,179	44,147	18,005	4,621
Individually assessed allowance for credit loss	694	1,531
Consumer and other
Financing Receivable, Allowance for Credit Loss [Line Items]
Type of Collateral	10,404	11,240	$ 6,819	$ 3,002
Individually assessed allowance for credit loss	1	1
Real Estate
Financing Receivable, Allowance for Credit Loss [Line Items]
Type of Collateral	35,175	16,832
Real Estate | Commercial and industrial
Financing Receivable, Allowance for Credit Loss [Line Items]
Type of Collateral	1,449	0
Real Estate | Construction
Financing Receivable, Allowance for Credit Loss [Line Items]
Type of Collateral	5,513	3,877
Real Estate | Residential real estate | 1-to-4 family mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
Type of Collateral	1,725	226
Real Estate | Residential real estate | Residential line of credit
Financing Receivable, Allowance for Credit Loss [Line Items]
Type of Collateral	1,256	1,174
Real Estate | Residential real estate | Multi-family mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
Type of Collateral	0	0
Real Estate | Commercial real estate | Owner occupied
Financing Receivable, Allowance for Credit Loss [Line Items]
Type of Collateral	13,451	3,391
Real Estate | Commercial real estate | Non-owner occupied
Financing Receivable, Allowance for Credit Loss [Line Items]
Type of Collateral	11,781	8,164
Real Estate | Consumer and other
Financing Receivable, Allowance for Credit Loss [Line Items]
Type of Collateral	0	0
Financial Assets and Equipment
Financing Receivable, Allowance for Credit Loss [Line Items]
Type of Collateral	12,255	1,728
Financial Assets and Equipment | Commercial and industrial
Financing Receivable, Allowance for Credit Loss [Line Items]
Type of Collateral	11,770	1,728
Financial Assets and Equipment | Construction
Financing Receivable, Allowance for Credit Loss [Line Items]
Type of Collateral	0	0
Financial Assets and Equipment | Residential real estate | 1-to-4 family mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
Type of Collateral	0	0
Financial Assets and Equipment | Residential real estate | Residential line of credit
Financing Receivable, Allowance for Credit Loss [Line Items]
Type of Collateral	0	0
Financial Assets and Equipment | Residential real estate | Multi-family mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
Type of Collateral	485	0
Financial Assets and Equipment | Commercial real estate | Owner occupied
Financing Receivable, Allowance for Credit Loss [Line Items]
Type of Collateral	0	0
Financial Assets and Equipment | Commercial real estate | Non-owner occupied
Financing Receivable, Allowance for Credit Loss [Line Items]
Type of Collateral	0	0
Financial Assets and Equipment | Consumer and other
Financing Receivable, Allowance for Credit Loss [Line Items]
Type of Collateral	0	0
Collateral Pledged
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually assessed allowance for credit loss	1,001	1,687
Collateral Pledged | Commercial and industrial
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually assessed allowance for credit loss	230	117
Collateral Pledged | Construction
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually assessed allowance for credit loss	0	0
Collateral Pledged | Residential real estate | 1-to-4 family mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually assessed allowance for credit loss	0	0
Collateral Pledged | Residential real estate | Residential line of credit
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually assessed allowance for credit loss	8	9
Collateral Pledged | Residential real estate | Multi-family mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually assessed allowance for credit loss	0	0
Collateral Pledged | Commercial real estate | Owner occupied
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually assessed allowance for credit loss	69	30
Collateral Pledged | Commercial real estate | Non-owner occupied
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually assessed allowance for credit loss	694	1,531
Collateral Pledged | Consumer and other
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually assessed allowance for credit loss	$ 0	$ 0