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Merger - Business Acquisition, Pro Forma Information (Details) - American River Bank (ARB) Merger - USD ($) $ in Thousands | 5 Months Ended | 12 Months Ended
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Dec. 31, 2021 | Dec. 31, 2021 | Dec. 31, 2020
Business Acquisition, Pro Forma Information [Abstract] |  |  |
Net interest income - Pro forma | $ 9,167 | $ 120,513 | $ 122,608
Net interest income - Actual |  | 104,951 | 96,659
Net income - Pro forma | $ (1,444) | 42,997 | 28,445
Net income - Actual |  | 33,228 | 30,242
Total merger-related one-time and conversion costs |  | 6,458 | $ 0
American River Bank ARB |  |  |
Business Acquisition, Pro Forma Information [Abstract] |  |  |
Total merger-related one-time and conversion costs |  | 3,000 |
Bank of Marin |  |  |
Business Acquisition, Pro Forma Information [Abstract] |  |  |
Total merger-related one-time and conversion costs |  | $ 4,900 |

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