Loans and Allowance for Credit Losses on Loans - Outstanding and Aging Analysis (Details)	9 Months Ended
	Sep. 30, 2021 USD ($) loan	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	$ 2,317,019,000		$ 2,088,556,000
Non-accrual loans with no allowance	8,423,000		9,233,000
Loans past due more than 90 days still accruing	0		0
Financing receivable, nonaccrual, earning interest on cash basis	0		0
Financing receivable, nonaccrual, interest income	$ 0	$ 0
Financing receivable, number of loans placed on nonaccrual status \| loan	0
Financing receivable, accrued interest, writeoff		$ 20,000
Commercial loans \| Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	$ 377,965,000		498,408,000
Non-accrual loans with no allowance	0		0
Commercial real estate loans \| American River Bank (ARB)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	118,000
Commercial real estate loans \| Commercial owner-occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	398,543,000		304,963,000
Non-accrual loans with no allowance	7,273,000		7,147,000
Commercial real estate loans \| Commercial investor-owned
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	1,157,344,000		961,208,000
Non-accrual loans with no allowance	709,000		1,610,000
Commercial real estate loans \| Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	125,060,000		73,046,000
Non-accrual loans with no allowance	0		0
Residential loans \| Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	92,396,000		104,813,000
Non-accrual loans with no allowance	441,000		459,000
Residential loans \| Other residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	117,778,000		123,395,000
Non-accrual loans with no allowance	0		0
Consumer loans \| Installment and other consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	47,933,000		22,723,000
Non-accrual loans with no allowance	0		17,000
Financial asset, other than financial asset acquired with credit deterioration
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	2,317,019,000		2,088,556,000
Non-accrual	8,423,000
Financial asset, other than financial asset acquired with credit deterioration \| 30-59 days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	397,000		2,083,000
Non-accrual			9,233,000
Financial asset, other than financial asset acquired with credit deterioration \| 60-89 days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	1,046,000		622,000
Financial asset, other than financial asset acquired with credit deterioration \| 90 days or more past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	0		0
Financial asset, other than financial asset acquired with credit deterioration \| Total past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	1,443,000		2,705,000
Financial asset, other than financial asset acquired with credit deterioration \| Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	2,315,576,000		2,085,851,000
Financial asset, other than financial asset acquired with credit deterioration \| Commercial loans \| Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	377,965,000		498,408,000
Non-accrual	0
Financial asset, other than financial asset acquired with credit deterioration \| Commercial loans \| Commercial and industrial \| 30-59 days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	181,000		0
Non-accrual			0
Financial asset, other than financial asset acquired with credit deterioration \| Commercial loans \| Commercial and industrial \| 60-89 days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	924,000		0
Financial asset, other than financial asset acquired with credit deterioration \| Commercial loans \| Commercial and industrial \| 90 days or more past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	0		0
Financial asset, other than financial asset acquired with credit deterioration \| Commercial loans \| Commercial and industrial \| Total past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	1,105,000		0
Financial asset, other than financial asset acquired with credit deterioration \| Commercial loans \| Commercial and industrial \| Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	376,860,000		498,408,000
Financial asset, other than financial asset acquired with credit deterioration \| Commercial real estate loans \| Commercial owner-occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	398,543,000		304,963,000
Non-accrual	7,273,000
Financial asset, other than financial asset acquired with credit deterioration \| Commercial real estate loans \| Commercial owner-occupied \| 30-59 days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	0		0
Non-accrual			7,147,000
Financial asset, other than financial asset acquired with credit deterioration \| Commercial real estate loans \| Commercial owner-occupied \| 60-89 days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	0		0
Financial asset, other than financial asset acquired with credit deterioration \| Commercial real estate loans \| Commercial owner-occupied \| 90 days or more past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	0		0
Financial asset, other than financial asset acquired with credit deterioration \| Commercial real estate loans \| Commercial owner-occupied \| Total past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	0		0
Financial asset, other than financial asset acquired with credit deterioration \| Commercial real estate loans \| Commercial owner-occupied \| Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	398,543,000		304,963,000
Financial asset, other than financial asset acquired with credit deterioration \| Commercial real estate loans \| Commercial investor-owned
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	1,157,344,000		961,208,000
Non-accrual	709,000
Financial asset, other than financial asset acquired with credit deterioration \| Commercial real estate loans \| Commercial investor-owned \| 30-59 days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	0		1,673,000
Non-accrual			1,610,000
Financial asset, other than financial asset acquired with credit deterioration \| Commercial real estate loans \| Commercial investor-owned \| 60-89 days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	0		0
Financial asset, other than financial asset acquired with credit deterioration \| Commercial real estate loans \| Commercial investor-owned \| 90 days or more past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost			0
Financial asset, other than financial asset acquired with credit deterioration \| Commercial real estate loans \| Commercial investor-owned \| Total past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	0		1,673,000
Financial asset, other than financial asset acquired with credit deterioration \| Commercial real estate loans \| Commercial investor-owned \| Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	1,157,344,000		959,535,000
Financial asset, other than financial asset acquired with credit deterioration \| Commercial real estate loans \| Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	125,060,000		73,046,000
Non-accrual	0
Financial asset, other than financial asset acquired with credit deterioration \| Commercial real estate loans \| Construction \| 30-59 days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	0		0
Non-accrual			0
Financial asset, other than financial asset acquired with credit deterioration \| Commercial real estate loans \| Construction \| 60-89 days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	0		0
Financial asset, other than financial asset acquired with credit deterioration \| Commercial real estate loans \| Construction \| 90 days or more past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	0		0
Financial asset, other than financial asset acquired with credit deterioration \| Commercial real estate loans \| Construction \| Total past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	0		0
Financial asset, other than financial asset acquired with credit deterioration \| Commercial real estate loans \| Construction \| Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	125,060,000		73,046,000
Financial asset, other than financial asset acquired with credit deterioration \| Residential loans \| Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	92,396,000		104,813,000
Non-accrual	441,000
Financial asset, other than financial asset acquired with credit deterioration \| Residential loans \| Home equity \| 30-59 days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	143,000		274,000
Non-accrual			459,000
Financial asset, other than financial asset acquired with credit deterioration \| Residential loans \| Home equity \| 60-89 days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	121,000		0
Financial asset, other than financial asset acquired with credit deterioration \| Residential loans \| Home equity \| 90 days or more past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	0		0
Financial asset, other than financial asset acquired with credit deterioration \| Residential loans \| Home equity \| Total past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	264,000		274,000
Financial asset, other than financial asset acquired with credit deterioration \| Residential loans \| Home equity \| Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	92,132,000		104,539,000
Financial asset, other than financial asset acquired with credit deterioration \| Residential loans \| Other residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	117,778,000		123,395,000
Non-accrual	0
Financial asset, other than financial asset acquired with credit deterioration \| Residential loans \| Other residential \| 30-59 days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	0		0
Non-accrual			0
Financial asset, other than financial asset acquired with credit deterioration \| Residential loans \| Other residential \| 60-89 days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	0		0
Financial asset, other than financial asset acquired with credit deterioration \| Residential loans \| Other residential \| 90 days or more past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	0		0
Financial asset, other than financial asset acquired with credit deterioration \| Residential loans \| Other residential \| Total past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	0		0
Financial asset, other than financial asset acquired with credit deterioration \| Residential loans \| Other residential \| Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	117,778,000		123,395,000
Financial asset, other than financial asset acquired with credit deterioration \| Consumer loans \| Installment and other consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	47,933,000		22,723,000
Non-accrual	0
Financial asset, other than financial asset acquired with credit deterioration \| Consumer loans \| Installment and other consumer loans \| 30-59 days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	73,000		136,000
Non-accrual			17,000
Financial asset, other than financial asset acquired with credit deterioration \| Consumer loans \| Installment and other consumer loans \| 60-89 days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	1,000		622,000
Financial asset, other than financial asset acquired with credit deterioration \| Consumer loans \| Installment and other consumer loans \| 90 days or more past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	0		0
Financial asset, other than financial asset acquired with credit deterioration \| Consumer loans \| Installment and other consumer loans \| Total past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	74,000		758,000
Financial asset, other than financial asset acquired with credit deterioration \| Consumer loans \| Installment and other consumer loans \| Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	$ 47,859,000		$ 21,965,000