Loans and allowance for loan losses - Nonaccrual TDRs and the related specific valuation allowance by portfolio segment (Details) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2022 USD ($) loan	Sep. 30, 2021 loan	Dec. 31, 2021 USD ($) loan
Information concerning Troubled Debt Restructurings
Recorded Investment	$ 5,240		$ 6,485
Number of Loans | loan	25	1	28
Specific Valuation Allowance
Information concerning Troubled Debt Restructurings
Recorded Investment	$ 9		$ 11
Number of Loans | loan	2		3
Performing Financing Receivable
Information concerning Troubled Debt Restructurings
Recorded Investment	$ 4,890		$ 5,734
Number of Loans | loan	22		23
Nonperforming Financial Instruments
Information concerning Troubled Debt Restructurings
Recorded Investment	$ 350		$ 751
Number of Loans | loan	3		5
Commercial real estate
Information concerning Troubled Debt Restructurings
Recorded Investment	$ 3,708		$ 4,701
Commercial real estate | Specific Valuation Allowance
Information concerning Troubled Debt Restructurings
Recorded Investment	3		4
Commercial real estate | Performing Financing Receivable
Information concerning Troubled Debt Restructurings
Recorded Investment	3,433		4,415
Commercial real estate | Nonperforming Financial Instruments
Information concerning Troubled Debt Restructurings
Recorded Investment	275		286
Consumer real estate secured by 1-4 family residential
Information concerning Troubled Debt Restructurings
Recorded Investment	1,513		1,765
Consumer real estate secured by 1-4 family residential | Specific Valuation Allowance
Information concerning Troubled Debt Restructurings
Recorded Investment	6		7
Consumer real estate secured by 1-4 family residential | Performing Financing Receivable
Information concerning Troubled Debt Restructurings
Recorded Investment	1,457		1,319
Consumer real estate secured by 1-4 family residential | Nonperforming Financial Instruments
Information concerning Troubled Debt Restructurings
Recorded Investment	56		446
Owner occupied | Commercial real estate
Information concerning Troubled Debt Restructurings
Recorded Investment	3,119		3,243
Owner occupied | Commercial real estate | Specific Valuation Allowance
Information concerning Troubled Debt Restructurings
Recorded Investment	3		4
Owner occupied | Commercial real estate | Performing Financing Receivable
Information concerning Troubled Debt Restructurings
Recorded Investment	3,119		3,243
Non-owner occupied | Commercial real estate
Information concerning Troubled Debt Restructurings
Recorded Investment	589		1,458
Non-owner occupied | Commercial real estate | Performing Financing Receivable
Information concerning Troubled Debt Restructurings
Recorded Investment	314		1,172
Non-owner occupied | Commercial real estate | Nonperforming Financial Instruments
Information concerning Troubled Debt Restructurings
Recorded Investment	275		286
First deed of trust | Consumer real estate secured by 1-4 family residential
Information concerning Troubled Debt Restructurings
Recorded Investment	1,422		1,666
First deed of trust | Consumer real estate secured by 1-4 family residential | Specific Valuation Allowance
Information concerning Troubled Debt Restructurings
Recorded Investment	6		7
First deed of trust | Consumer real estate secured by 1-4 family residential | Performing Financing Receivable
Information concerning Troubled Debt Restructurings
Recorded Investment	1,422		1,279
First deed of trust | Consumer real estate secured by 1-4 family residential | Nonperforming Financial Instruments
Information concerning Troubled Debt Restructurings
Recorded Investment			387
Second deed of trust | Consumer real estate secured by 1-4 family residential
Information concerning Troubled Debt Restructurings
Recorded Investment	91		99
Second deed of trust | Consumer real estate secured by 1-4 family residential | Performing Financing Receivable
Information concerning Troubled Debt Restructurings
Recorded Investment	35		40
Second deed of trust | Consumer real estate secured by 1-4 family residential | Nonperforming Financial Instruments
Information concerning Troubled Debt Restructurings
Recorded Investment	56		59
Commercial and industrial loans (except those secured by real estate) | Commercial and industrial loans
Information concerning Troubled Debt Restructurings
Recorded Investment	19		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		$ 19