Loans and allowance for credit losses - Interest Income Recognized on Non-accrual Loans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Financing Receivable, Impaired [Line Items]
Interest income recognized on non-accrual loans	$ 627	$ 205	$ 1,012	$ 432
Commercial and industrial
Financing Receivable, Impaired [Line Items]
Interest income recognized on non-accrual loans	219	17	333	169
Construction
Financing Receivable, Impaired [Line Items]
Interest income recognized on non-accrual loans	16	6	30	33
Residential real estate | 1-to-4 family mortgage
Financing Receivable, Impaired [Line Items]
Interest income recognized on non-accrual loans	67	6	85	13
Residential real estate | Residential line of credit
Financing Receivable, Impaired [Line Items]
Interest income recognized on non-accrual loans	27	0	45	1
Residential real estate | Multi-family mortgage
Financing Receivable, Impaired [Line Items]
Interest income recognized on non-accrual loans	1	0	2	0
Commercial real estate | Owner occupied
Financing Receivable, Impaired [Line Items]
Interest income recognized on non-accrual loans	101	43	232	64
Commercial real estate | Non-owner occupied
Financing Receivable, Impaired [Line Items]
Interest income recognized on non-accrual loans	141	109	230	128
Consumer and other
Financing Receivable, Impaired [Line Items]
Interest income recognized on non-accrual loans	$ 55	$ 24	$ 55	$ 24