Loans and allowance for loan losses - Financial Effect of TDRs (Details) $ in Thousands	12 Months Ended
Dec. 31, 2019 USD ($) loan	Dec. 31, 2018 USD ($) loan	Dec. 31, 2017 USD ($) loan
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans \| loan	12	9	7
Pre-modification outstanding recorded investment	$ 7,657	$ 1,340	$ 1,883
Post-modification outstanding recorded investment	7,658	1,340	1,883
Charge offs and specific reserves	$ 115	$ 0	$ 76
Residential line of credit
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans \| loan	2
Pre-modification outstanding recorded investment	$ 333
Post-modification outstanding recorded investment	333
Charge offs and specific reserves	$ 9
Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans \| loan	3	2	2
Pre-modification outstanding recorded investment	$ 3,204	$ 887	$ 627
Post-modification outstanding recorded investment	3,204	887	627
Charge offs and specific reserves	$ 0	$ 0	$ 0
Construction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans \| loan	2
Pre-modification outstanding recorded investment	$ 1,085
Post-modification outstanding recorded investment	1,085
Charge offs and specific reserves	$ 0
Commercial real estate: \| Owner occupied
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans \| loan	2	1	1
Pre-modification outstanding recorded investment	$ 1,494	$ 143	$ 377
Post-modification outstanding recorded investment	1,495	143	377
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
Pre-modification outstanding recorded investment	$ 1,366		$ 711
Post-modification outstanding recorded investment	1,366		711
Charge offs and specific reserves	$ 106		$ 68
Residential real estate: \| 1-to-4 family mortgage
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans \| loan	2	1	1
Pre-modification outstanding recorded investment	$ 175	$ 249	$ 143
Post-modification outstanding recorded investment	175	249	143
Charge offs and specific reserves	$ 0	$ 0	$ 8
Residential real estate: \| Consumer and other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans \| loan		5	1
Pre-modification outstanding recorded investment		$ 61	$ 25
Post-modification outstanding recorded investment		61	25
Charge offs and specific reserves		$ 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=118936363&loc=SL6953676-111524

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

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- Definition

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

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