Loans and allowance for credit losses - Allowance for Credit Losses by Class of Financing Receivable Disaggregated by Measurement Methodology (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for credit loss	$ 943		$ 2,039
Collectively evaluated for credit loss	124,750		149,405
Total	144,663	$ 157,954	170,389	$ 113,129	$ 89,141	$ 31,139
Purchased Credit Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	18,970		18,945
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for credit loss	105		373
Collectively evaluated for credit loss	13,073		13,493
Total	13,791	14,643	14,748	8,878	10,881	4,805
Commercial and industrial | Purchased Credit Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	613		882
Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for credit loss	131		95
Collectively evaluated for credit loss	31,151		54,065
Total	32,838	38,622	58,477	35,599	22,842	10,194
Construction | Purchased Credit Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	1,556		4,317
Residential real estate | 1-to-4 family mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for credit loss	0		0
Collectively evaluated for credit loss	18,063		17,206
Total	19,672	19,572	19,220	12,463	13,006	3,112
Residential real estate | 1-to-4 family mortgage | Purchased Credit Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	1,609		2,014
Residential real estate | Residential line of credit
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for credit loss	8		9
Collectively evaluated for credit loss	6,467		10,031
Total	6,716	9,268	10,534	6,811	6,213	752
Residential real estate | Residential line of credit | Purchased Credit Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	241		494
Residential real estate | Multi-family mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for credit loss	0		0
Collectively evaluated for credit loss	12,976		6,326
Total	13,475	11,657	7,174	4,499	2,328	544
Residential real estate | Multi-family mortgage | Purchased Credit Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	499		848
Commercial real estate | Owner occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for credit loss	23		30
Collectively evaluated for credit loss	4,015		4,062
Total	4,707	3,609	4,849	7,420	9,047	4,109
Commercial real estate | Owner occupied | Purchased Credit Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	669		757
Commercial real estate | Non-owner occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for credit loss	676		1,531
Collectively evaluated for credit loss	29,020		33,706
Total	42,856	50,179	44,147	30,444	18,005	4,621
Commercial real estate | Non-owner occupied | Purchased Credit Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	13,160		8,910
Consumer and other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for credit loss	0		1
Collectively evaluated for credit loss	9,985		10,516
Total	10,608	$ 10,404	11,240	$ 7,015	$ 6,819	$ 3,002
Consumer and other | Purchased Credit Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	$ 623		$ 723