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Merger Agreement - Narrative (Details) $ in Thousands	Jun. 30, 2021 USD ($)	Apr. 16, 2021 branch shares	Dec. 31, 2020 USD ($)
Business Combination, Separately Recognized Transactions [Line Items]
Assets	$ 3,073,818		$ 2,911,926
Deposits	2,683,575		2,504,249
Loans at amortized cost	2,002,767		$ 2,088,556
American River Bank (ARB) Merger | American River Bank (ARB)
Business Combination, Separately Recognized Transactions [Line Items]
Number of branches | branch		10
Assets	906,100
Deposits	787,700
Loans at amortized cost	$ 434,200
American River Bank (ARB) Merger | Bank of Marin
Business Combination, Separately Recognized Transactions [Line Items]
Merger agreement, shares exchange ratio (in shares) | shares		0.575

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