Loans and allowance for credit losses - Nonaccrual TDRs and the related specific valuation allowance by portfolio segment (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2022 USD ($) loan
Information concerning Troubled Debt Restructurings
Recorded Investment	$ 5,163
New TDR identifications | loan	0
Number of Loans | loan	24
Specific Valuation Allowance
Information concerning Troubled Debt Restructurings
Recorded Investment	$ 8
Number of Loans | loan	3
Performing Financing Receivable
Information concerning Troubled Debt Restructurings
Recorded Investment	$ 5,088
Number of Loans | loan	22
Nonperforming Financial Instruments
Information concerning Troubled Debt Restructurings
Recorded Investment	$ 75
Number of Loans | loan	2
Commercial real estate
Information concerning Troubled Debt Restructurings
Recorded Investment	$ 3,660
Commercial real estate | Specific Valuation Allowance
Information concerning Troubled Debt Restructurings
Recorded Investment	2
Commercial real estate | Performing Financing Receivable
Information concerning Troubled Debt Restructurings
Recorded Investment	3,660
Consumer real estate secured by 1-4 family residential
Information concerning Troubled Debt Restructurings
Recorded Investment	1,484
Consumer real estate secured by 1-4 family residential | Specific Valuation Allowance
Information concerning Troubled Debt Restructurings
Recorded Investment	6
Consumer real estate secured by 1-4 family residential | Performing Financing Receivable
Information concerning Troubled Debt Restructurings
Recorded Investment	1,428
Consumer real estate secured by 1-4 family residential | Nonperforming Financial Instruments
Information concerning Troubled Debt Restructurings
Recorded Investment	56
Owner occupied | Commercial real estate
Information concerning Troubled Debt Restructurings
Recorded Investment	3,348
Owner occupied | Commercial real estate | Specific Valuation Allowance
Information concerning Troubled Debt Restructurings
Recorded Investment	2
Owner occupied | Commercial real estate | Performing Financing Receivable
Information concerning Troubled Debt Restructurings
Recorded Investment	3,348
Non-owner occupied | Commercial real estate
Information concerning Troubled Debt Restructurings
Recorded Investment	312
Non-owner occupied | Commercial real estate | Performing Financing Receivable
Information concerning Troubled Debt Restructurings
Recorded Investment	312
First deed of trust | Consumer real estate secured by 1-4 family residential
Information concerning Troubled Debt Restructurings
Recorded Investment	1,409
First deed of trust | Consumer real estate secured by 1-4 family residential | Specific Valuation Allowance
Information concerning Troubled Debt Restructurings
Recorded Investment	6
First deed of trust | Consumer real estate secured by 1-4 family residential | Performing Financing Receivable
Information concerning Troubled Debt Restructurings
Recorded Investment	1,409
Second deed of trust | Consumer real estate secured by 1-4 family residential
Information concerning Troubled Debt Restructurings
Recorded Investment	75
Second deed of trust | Consumer real estate secured by 1-4 family residential | Performing Financing Receivable
Information concerning Troubled Debt Restructurings
Recorded Investment	19
Second deed of trust | Consumer real estate secured by 1-4 family residential | Nonperforming Financial Instruments
Information concerning Troubled Debt Restructurings
Recorded Investment	56
Commercial and industrial loans (except those secured by real estate) | Commercial and industrial loans
Information concerning Troubled Debt Restructurings
Recorded Investment	19
Commercial and industrial loans (except those secured by real estate) | Commercial and industrial loans | Nonperforming Financial Instruments
Information concerning Troubled Debt Restructurings
Recorded Investment	$ 19