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Acquisition - Narrative (Details) | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2017 USD ($) | Nov. 21, 2017 USD ($) branch | Dec. 31, 2016 USD ($)
Business Acquisition [Line Items] |  |  |
Goodwill | $ 30,140,000 |  | $ 6,436,000
Impairment on goodwill | $ 0 |  |
Minimum |  |  |
Business Acquisition [Line Items] |  |  |
Constant prepayment rate (CPR) | 5.00% |  |
Maximum |  |  |
Business Acquisition [Line Items] |  |  |
Constant prepayment rate (CPR) | 27.00% |  |
Bank of Napa, N.A. (Napa) |  |  |
Business Acquisition [Line Items] |  |  |
Loans acquired |  | $ 134,700,000 |
Deposits assumed |  | 249,886,000 |
Investment securities acquired |  | $ 75,469,000 |
Number of branch offices | branch |  | 2 |
Shares received by Napa shareholders in merger per acquiree share |  | 0.307 |
Goodwill |  | $ 23,705,000 |

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