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Summary of Significant Accounting Policies - Narrative (Details) $ in Thousands | 12 Months Ended
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Dec. 31, 2016 USD ($) payment branch | Dec. 31, 2015 USD ($) | Dec. 31, 2014 USD ($)
Entity Location [Line Items] |  |  |
Number of consecutive payments considered sustained repayment performance | payment | 6 |  |
Threshold period a past due loan is charged off | 90 days |  |
Threshold period a past due overdraft account is charged off | 60 days |  |
Ownership interest in each limited partnerships formed for affordable housing projects (less than) | 2.00% |  |
Advertising costs | $ | $ 565 | $ 334 | $ 400
Commitments under operating leases | $ | $ 21,082 |  |
Marin County |  |  |
Entity Location [Line Items] |  |  |
Number of branches | 10 |  |
Napa County |  |  |
Entity Location [Line Items] |  |  |
Number of branches | 1 |  |
San Francisco |  |  |
Entity Location [Line Items] |  |  |
Number of branches | 1 |  |
Sonoma County |  |  |
Entity Location [Line Items] |  |  |
Number of branches | 5 |  |
Alameda County |  |  |
Entity Location [Line Items] |  |  |
Number of branches | 3 |  |

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