Loans and Allowance for Credit Losses on Loans - Outstanding and Aging Analysis (Details)	6 Months Ended
	Jun. 30, 2021 USD ($) loan	Jun. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	$ 2,002,767,000		$ 2,088,556,000
Non-accrual loans with no allowance	9,190,000		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	$ 423,646,000		498,408,000
Non-accrual loans with no allowance	0		0
Commercial real estate loans \| Commercial owner-occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	296,407,000		304,963,000
Non-accrual loans with no allowance	7,148,000		7,147,000
Commercial real estate loans \| Commercial investor-owned
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	967,335,000		961,208,000
Non-accrual loans with no allowance	1,597,000		1,610,000
Commercial real estate loans \| Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	80,841,000		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	92,510,000		104,813,000
Non-accrual loans with no allowance	445,000		459,000
Residential loans \| Other residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	120,903,000		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	21,125,000		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	2,002,767,000		2,088,556,000
Non-accrual	9,190,000
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	1,366,000		2,705,000
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	367,000		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	121,000		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	878,000		0
Financial asset, other than financial asset acquired with credit deterioration \| Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	2,001,401,000		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	423,646,000		498,408,000
Non-accrual	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	367,000		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	367,000		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	0		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 \| Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	423,279,000		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	296,407,000		304,963,000
Non-accrual	7,148,000
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 \| 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 \| Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	296,407,000		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	967,335,000		961,208,000
Non-accrual	1,597,000
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	878,000		1,673,000
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	878,000		0
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	966,457,000		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	80,841,000		73,046,000
Non-accrual	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 \| 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 \| Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	80,841,000		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	92,510,000		104,813,000
Non-accrual	445,000
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	121,000		274,000
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	0		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 \| Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	92,389,000		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	120,903,000		123,395,000
Non-accrual	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 \| 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 \| Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	120,903,000		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	21,125,000		22,723,000
Non-accrual	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	0		758,000
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	0		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	0		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 \| Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans at amortized cost	$ 21,125,000		$ 21,965,000