Loans and allowance for credit losses - Aging of recorded investment in past due loans and leases (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		$ 538,427
Total loans	$ 566,101
Recorded Investment, 90 Days and Accruing		1,725
Recorded Investment, 90 Days and Accruing	2,445
Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		533,978
Total loans	562,054
Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		4,449
Total loans	4,047
30 to 59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		1,907
Total loans	887
60 to 89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		440
Total loans	715
Greater than 90 Days
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		2,102
Total loans	2,445
Construction and land development
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		45,127
Total loans	56,260
Construction and land development | Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		45,127
Total loans	56,260
Construction and land development | Residential
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		9,727
Total loans	8,848
Construction and land development | Residential | Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		9,727
Total loans	8,848
Construction and land development | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		35,400
Total loans	47,412
Construction and land development | Commercial | Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		35,400
Total loans	47,412
Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		284,617
Total loans	286,281
Commercial real estate | Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		284,617
Total loans	286,281
Commercial real estate | Owner occupied
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		119,643
Total loans	121,652
Commercial real estate | Owner occupied | Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		119,643
Total loans	121,652
Commercial real estate | Non-owner occupied
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		153,610
Total loans	151,445
Commercial real estate | Non-owner occupied | Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		153,610
Total loans	151,445
Commercial real estate | Multifamily
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		11,291
Total loans	12,827
Commercial real estate | Multifamily | Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		11,291
Total loans	12,827
Commercial real estate | Farmland
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		73
Total loans	357
Commercial real estate | Farmland | Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		73
Total loans	357
Consumer real estate secured by 1-4 family residential
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		93,680
Total loans	117,014
Consumer real estate secured by 1-4 family residential | Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		93,576
Total loans	116,712
Consumer real estate secured by 1-4 family residential | Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		104
Total loans	302
Consumer real estate secured by 1-4 family residential | 30 to 59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		54
Total loans	102
Consumer real estate secured by 1-4 family residential | 60 to 89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		50
Total loans	200
Consumer real estate secured by 1-4 family residential | Home equity lines
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		18,421
Total loans	18,299
Consumer real estate secured by 1-4 family residential | Home equity lines | Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		18,371
Total loans	18,099
Consumer real estate secured by 1-4 family residential | Home equity lines | Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		50
Total loans	200
Consumer real estate secured by 1-4 family residential | Home equity lines | 60 to 89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		50
Total loans	200
Consumer real estate secured by 1-4 family residential | First deed of trust
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		67,495
Total loans	88,182
Consumer real estate secured by 1-4 family residential | First deed of trust | Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		67,495
Total loans	88,113
Consumer real estate secured by 1-4 family residential | First deed of trust | Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	69
Consumer real estate secured by 1-4 family residential | First deed of trust | 30 to 59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	69
Consumer real estate secured by 1-4 family residential | Second deed of trust
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		7,764
Total loans	10,533
Consumer real estate secured by 1-4 family residential | Second deed of trust | Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		7,710
Total loans	10,500
Consumer real estate secured by 1-4 family residential | Second deed of trust | Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		54
Total loans	33
Consumer real estate secured by 1-4 family residential | Second deed of trust | 30 to 59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		54
Total loans	33
Consumer real estate secured by 1-4 family residential | Consumer and other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		4,038
Total loans	4,578
Commercial and industrial loans | Commercial and industrial loans (except those secured by real estate)
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		90,348
Total loans	83,045
Recorded Investment, 90 Days and Accruing	47
Commercial and industrial loans | Commercial and industrial loans (except those secured by real estate) | Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		88,949
Total loans	82,998
Commercial and industrial loans | Commercial and industrial loans (except those secured by real estate) | Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		1,399
Total loans	47
Commercial and industrial loans | Commercial and industrial loans (except those secured by real estate) | 30 to 59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		1,022
Commercial and industrial loans | Commercial and industrial loans (except those secured by real estate) | Greater than 90 Days
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		377
Total loans	47
Commercial and industrial loans | Guaranteed student loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		20,617
Total loans	18,923
Recorded Investment, 90 Days and Accruing		1,725
Recorded Investment, 90 Days and Accruing	2,398
Commercial and industrial loans | Guaranteed student loans | Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		17,671
Total loans	15,227
Commercial and industrial loans | Guaranteed student loans | Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		2,946
Total loans	3,696
Commercial and industrial loans | Guaranteed student loans | 30 to 59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		831
Total loans	783
Commercial and industrial loans | Guaranteed student loans | 60 to 89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		390
Total loans	515
Commercial and industrial loans | Guaranteed student loans | Greater than 90 Days
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		1,725
Total loans	2,398
Commercial and industrial loans | Consumer and other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		4,038
Total loans	4,578
Commercial and industrial loans | Consumer and other | Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		$ 4,038
Total loans	4,576
Commercial and industrial loans | Consumer and other | Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	2
Commercial and industrial loans | Consumer and other | 30 to 59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	$ 2