Loans and allowance for credit losses - Average Recorded Investment and Interest Income on Cash Basis Recognized on Impaired Loans (Details) $ in Thousands	12 Months Ended
Dec. 31, 2019 USD ($)
Average recorded investment
With a related allowance recorded	$ 10,568
With no related allowance recorded	8,197
Total impaired loans	18,765
Interest income recognized (cash basis)
With a related allowance recorded	624
With no related allowance recorded	575
Total impaired loans	1,199
Commercial and industrial
Average recorded investment
With a related allowance recorded	3,349
With no related allowance recorded	2,088
Interest income recognized (cash basis)
With a related allowance recorded	474
With no related allowance recorded	201
Construction
Average recorded investment
With no related allowance recorded	1,641
Interest income recognized (cash basis)
With no related allowance recorded	167
Residential real estate \| 1-to-4 family mortgage
Average recorded investment
With a related allowance recorded	205
With no related allowance recorded	963
Interest income recognized (cash basis)
With a related allowance recorded	13
With no related allowance recorded	68
Residential real estate \| Residential line of credit
Average recorded investment
With no related allowance recorded	252
Interest income recognized (cash basis)
With no related allowance recorded	1
Commercial real estate \| Owner occupied
Average recorded investment
With a related allowance recorded	658
With no related allowance recorded	2,143
Interest income recognized (cash basis)
With a related allowance recorded	27
With no related allowance recorded	133
Commercial real estate \| Non-owner occupied
Average recorded investment
With a related allowance recorded	6,196
With no related allowance recorded	1,049
Interest income recognized (cash basis)
With a related allowance recorded	109
With no related allowance recorded	0
Consumer and other
Average recorded investment
With no related allowance recorded	61
Interest income recognized (cash basis)
With no related allowance recorded	$ 5

Average amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=123577603&loc=d3e5212-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=123577603&loc=d3e5258-111524

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-SubTopic 10
-Section 50
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=123577603&loc=d3e5258-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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-Paragraph 15
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=123577603&loc=d3e5212-111524

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