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Borrowings - Lines of Credit and Borrowing Agreements (Details) - Line of Credit - USD ($) | Jun. 15, 2016 | Feb. 05, 2008 | Dec. 31, 2017 | Dec. 31, 2016
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Federal Home Loan Bank Borrowings |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |
Term of FHLB borrowing agreements |  | 10 years |  |
Principal amount of borrowing agreements with FHLB |  | $ 15,000,000.0 |  |
Fixed interest rate of FHLB borrowing agreement |  | 2.07% |  |
Amount of FHLB borrowings outstanding |  |  | $ 0 | $ 0
Federal Home Loan Bank |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |
Lines of credit |  |  | 538,900,000 | 513,700,000
Remaining available line of credit from FHLB |  |  | 538,900,000 | 513,700,000
Federal Home Loan Bank Borrowings |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |
Amount of debt repaid | $ 15,000,000 |  |  |
Federal Home Loan Bank Borrowings | Interest expense |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |
Prepayment fee on debt repaid | $ 312,000 |  |  |
Federal Funds Purchased |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |
Lines of credit |  |  | 100,400,000 | 92,000,000
Short-term Debt |  |  | 0 | 0
Federal Funds Purchased | Bank of Napa, N.A. (Napa) |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |
Lines of credit |  |  |  | 8,400,000
Federal Home Loan Bank Overnight Borrowings |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |
Short-term Debt |  |  | 0 |
Federal Home Loan Bank Borrowings |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |
Short-term Debt |  |  | 0 | 0
Federal Reserve Line of Credit |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |
Lines of credit |  |  | 52,100,000 | 43,100,000
Amount of FHLB borrowings outstanding |  |  | $ 0 | $ 0

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- Definition Long-term Debt, Contractual Term, Number of Years + References No definition available. + Details
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- Definition Contractual interest rate for funds borrowed, under the debt agreement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(1)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Including both current and noncurrent portions, Federal Home Loan Bank borrowings initially due beyond one year or beyond the normal operating cycle if longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 470 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=75038535&loc=d3e64702-112823 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.16) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 470 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6479118&loc=d3e64650-112822 + Details
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- Definition The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(16)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + Details
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- Definition Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Amount of cash outflow for cost from early extinguishment and prepayment of debt. Includes, but is not limited to, third-party cost, premium paid, and other fee paid to lender directly for debt extinguishment or debt prepayment. Excludes accrued interest. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 15 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3291-108585 + Details
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