Loans and allowance for credit losses - Financial Effect of TDRs (Details) $ in Thousands	3 Months Ended
Mar. 31, 2020 USD ($) loan	Mar. 31, 2019 USD ($) loan
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans \| loan	1	2
Pre-modification outstanding recorded investment	$ 64	$ 3,188
Post-modification outstanding recorded investment	64	3,188
Charge offs and specific reserves	$ 0	$ 0
Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans \| loan		2
Pre-modification outstanding recorded investment		$ 3,188
Post-modification outstanding recorded investment		3,188
Charge offs and specific reserves		$ 0
Residential real estate: \| 1-to-4 family mortgage
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans \| loan	1
Pre-modification outstanding recorded investment	$ 64
Post-modification outstanding recorded investment	64
Charge offs and specific reserves	$ 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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- 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.

+ References

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