Loans and allowance for credit losses - Financial Effect of TDRs (Details) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2020 USD ($) loan	Sep. 30, 2019 USD ($) loan	Sep. 30, 2020 USD ($) loan	Sep. 30, 2019 USD ($) loan
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans \| loan	2	5	8	7
Pre-modification outstanding recorded investment	$ 420	$ 3,507	$ 6,190	$ 6,695
Post-modification outstanding recorded investment	420	3,507	6,190	6,695
Charge offs and specific reserves	$ 0	$ 106	$ 0	$ 106
Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans \| loan	2	1	3	3
Pre-modification outstanding recorded investment	$ 420	$ 16	$ 1,573	$ 3,204
Post-modification outstanding recorded investment	420	16	1,573	3,204
Charge offs and specific reserves	$ 0	$ 0	$ 0	$ 0
Construction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans \| loan		1		1
Pre-modification outstanding recorded investment		$ 1,070		$ 1,070
Post-modification outstanding recorded investment		1,070		1,070
Charge offs and specific reserves				$ 0
Commercial real estate: \| Owner occupied
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans \| loan		1	1	1
Pre-modification outstanding recorded investment		$ 927	$ 788	$ 927
Post-modification outstanding recorded investment		927	788	927
Charge offs and specific reserves		$ 0	$ 0	$ 0
Commercial real estate: \| Non-owner occupied
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans \| loan		1	2	1
Pre-modification outstanding recorded investment		$ 1,366	$ 3,752	$ 1,366
Post-modification outstanding recorded investment		1,366	3,752	1,366
Charge offs and specific reserves		$ 106	$ 0	$ 106
Residential real estate: \| 1-to-4 family mortgage
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans \| loan		1	2	1
Pre-modification outstanding recorded investment		$ 128	$ 77	$ 128
Post-modification outstanding recorded investment		128	77	128
Charge offs and specific reserves		$ 0	$ 0	$ 0

Financing receivable modifications charge offs and specific reserves.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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- Definition

Number of financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953676-111524

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- Definition

Amount, after troubled debt restructuring, of modified financing receivable.

+ References

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- Definition

Amount, before troubled debt restructuring, of financing receivable to be modified.

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