Loans and allowance for loan losses - Financial Effect of TDRs (Details) $ in Thousands	12 Months Ended
Dec. 31, 2018 USD ($) loan	Dec. 31, 2017 USD ($) loan	Dec. 31, 2016 USD ($) loan
Financing Receivable, Modifications [Line Items]
Number of loans \| loan	9	7	9
Pre-modification outstanding recorded investment	$ 1,340	$ 1,883	$ 1,966
Post-modification outstanding recorded investment	1,340	1,883	1,966
Charge offs and specific reserves	$ 0	$ 76	$ 0
Consumer and other
Financing Receivable, Modifications [Line Items]
Number of loans \| loan	5	1	3
Pre-modification outstanding recorded investment	$ 61	$ 25	$ 29
Post-modification outstanding recorded investment	61	25	29
Charge offs and specific reserves	$ 0	$ 0	$ 0
Commercial and industrial
Financing Receivable, Modifications [Line Items]
Number of loans \| loan	2	2
Pre-modification outstanding recorded investment	$ 887	$ 627
Post-modification outstanding recorded investment	887	627
Charge offs and specific reserves	$ 0	$ 0
Commercial real estate: \| Owner occupied
Financing Receivable, Modifications [Line Items]
Number of loans \| loan	1	1	1
Pre-modification outstanding recorded investment	$ 143	$ 377	$ 118
Post-modification outstanding recorded investment	143	377	118
Charge offs and specific reserves	$ 0	$ 0	$ 0
Commercial real estate: \| Non-owner occupied
Financing Receivable, Modifications [Line Items]
Number of loans \| loan		2
Pre-modification outstanding recorded investment		$ 711
Post-modification outstanding recorded investment		711
Charge offs and specific reserves		$ 68
Residential real estate: \| 1-to-4 family mortgage
Financing Receivable, Modifications [Line Items]
Number of loans \| loan	1	1	5
Pre-modification outstanding recorded investment	$ 249	$ 143	$ 1,819
Post-modification outstanding recorded investment	249	143	1,819
Charge offs and specific reserves	$ 0	$ 8	$ 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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953676-111524

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- Definition

Post-modification amount of investment in financing receivables modified by troubled debt restructurings.

+ References

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- Definition

Pre-modification amount of investment in financing receivables modified by troubled debt restructurings.

+ References

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