Benefit Plans - Salary Continuation Plan (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Percentage of salary paid upon retirement	25.00%
Period before ratable vesting begins	5 years
Age ratable vesting ends	65 years
Liability under the Salary Continuation Plan	$ 2.5	$ 1.0
Bank of Napa, N.A. (Napa)
Defined Benefit Plan Disclosure [Line Items]
Liability under the Salary Continuation Plan	$ 1.2

Amount of asset (liability), recognized in statement of financial position, for defined benefit pension and other postretirement plans.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64852052&loc=d3e1703-114919

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant