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Acquisition - Narrative (Details) | 9 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Sep. 30, 2018 USD ($) | Sep. 30, 2017 USD ($) | Dec. 31, 2017 USD ($) | Nov. 21, 2017 USD ($) branch
Business Acquisition [Line Items] |  |  |  |
Goodwill | $ 30,140,000 |  | $ 30,140,000 |
Amortization of core deposit intangible | 690,000 | $ 354,000 |  |
Bank of Napa, N.A. (Napa) |  |  |  |
Business Acquisition [Line Items] |  |  |  |
Number of branch offices | branch |  |  |  | 2
Loans acquired |  |  |  | $ 134,700,000
Deposits assumed |  |  |  | 249,900,000
Investment securities acquired |  |  |  | $ 75,500,000
Shares received by Napa shareholders in acquisition per acquiree share |  |  |  | 0.307
Goodwill |  |  |  | $ 23,700,000
Goodwill impairment | 0 |  |  |
Core deposits | Bank of Napa, N.A. (Napa) |  |  |  |
Business Acquisition [Line Items] |  |  |  |
Core deposit intangible asset |  |  |  | $ 4,400,000
Amortization of core deposit intangible | $ 381,000 |  | $ 56,000 |
Useful life of core deposit intangible asset | 10 years |  |  |

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- Definition The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16323-109275 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6388964&loc=d3e16225-109274 + Details
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- Definition Amount of investments in debt and equity securities, including, but not limited to, held-to-maturity, trading and available-for-sale expected to be converted to cash, sold or exchanged within one year or the normal operating cycle, if longer, acquired at the acquisition date. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=84161108&loc=d3e4845-128472 + Details
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- Definition Amount due from customers or clients for goods or services, including trade receivables, that have been delivered or sold in the normal course of business, and amounts due from others, including related parties expected to be converted to cash, sold or exchanged within one year or the normal operating cycle, if longer, acquired at the acquisition date. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=84161108&loc=d3e4845-128472 + Details
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