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Commitments and contingencies Financial Instruments with Off-Balance Sheet Risk (Details) - USD ($) $ in Thousands | Jun. 30, 2018 | Dec. 31, 2017
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Commitments to Extend Credit [Member] |  |
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items] |  |
Fair Value Disclosure, Off-balance Sheet Risks, Face Amount, Liability | $ 2,536,434 | $ 2,443,478
Standby Letters of Credit [Member] |  |
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items] |  |
Fair Value Disclosure, Off-balance Sheet Risks, Face Amount, Liability | 16,132 | 15,534
Deferred standby letter of credit fees [Member] |  |
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items] |  |
Fair Value Disclosure, Off-balance Sheet Risks, Face Amount, Liability | $ 115 | $ 102

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- Definition The face amount of financial liabilities, which are not recognized in the financial statements (off-balance sheet) because they fail to meet some other criterion for recognition. + References No definition available. + Details
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Balance Type: | credit
Period Type: | instant

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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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- Details
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- Details
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- Details
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