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Loans and Allowance for Loan Losses - Troubled Debt Restructuring by Class (Details) | 12 Months Ended
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Dec. 31, 2017 USD ($) loan | Dec. 31, 2016 USD ($) loan | Dec. 31, 2015 USD ($) loan
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Number of loans removed from TDR resignation | loan | 0 | 0 | 5
Recorded investment of loans removed from TDR resignation |  |  | $ 1,600,000
Recorded investment in Troubled Debt Restructurings | $ 16,520,000 | $ 18,168,000 |
TDR loans accruing interest as of period end | 0 |  |
Acquired loans included in TDR | 0 |  |
Commercial | Commercial and industrial |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Recorded investment in Troubled Debt Restructurings | 2,165,000 | 2,207,000 |
Commercial real estate | Commercial real estate, owner-occupied |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Recorded investment in Troubled Debt Restructurings | 6,999,000 | 6,993,000 |
Commercial real estate | Commercial real estate, investor |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Recorded investment in Troubled Debt Restructurings | 2,171,000 | 2,256,000 |
Commercial real estate | Construction |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Recorded investment in Troubled Debt Restructurings | 2,969,000 | 3,245,000 |
Residential loans | Home equity |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Recorded investment in Troubled Debt Restructurings | 347,000 | 625,000 |
Residential loans | Other residential |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Recorded investment in Troubled Debt Restructurings | 1,148,000 | 1,965,000 |
Consumer loans | Installment and other consumer |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Recorded investment in Troubled Debt Restructurings | $ 721,000 | $ 877,000 |

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