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Loans - Narrative (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2021 USD ($) application	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) application Contract	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Period for order of valuations (at least)			18 months
Troubled debt restructured loans, balance	$ 3,679,000	$ 3,850,000	$ 3,679,000	$ 3,850,000
Number of loans which has periodic late payments | Contract			1
Financing Receivable, Modifications, Subsequent Default, Number of Contracts with Active Forbearance Agreements			0
Consumer mortgage loans secured by residential real estate properties for which formal foreclosure proceedings are in process	527,000		$ 527,000		$ 391,000
Recognized loan fee income	$ 17,689,000	19,861,000	$ 54,435,000	59,076,000
Residential mortgage and commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Threshold period past due to discontinue accrual interest on financing receivable			90 days
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Threshold period past due for write-off of financing receivable (no later than)	120 days		120 days
Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Period of financing receivable, updated valuation on real estate secured loans (number of days past due)			90 days
Number of previous months with no updated valuation completed for corporation to update valuation			12 months
Impaired financing receivable, valuation on real estate collateralized loans (number of days after the loan is classified as impaired)			30 days
CARES Act
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of applications | application	2,217		2,217
Total amount under PPP (up to)	$ 223,036,703		$ 223,036,703
Projected fee income			9,500,000
Recognized loan fee income	1,281,000	741,000	$ 4,411,000	1,417,000
Maximum | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable term			20 years
Loan-to-value ratio (no greater than)			80.00%
Maximum | Residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable term			30 years
Loan-to-value ratio (no greater than)			80.00%
Loan-to-value ratio that requires private mortgage insurance (in excess of)			80.00%
Maximum | Home equity lines of credit
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable term			20 years
Loan-to-value ratio (no greater than)			90.00%
Nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Troubled debt restructured loans, balance	79,000	143,000	$ 79,000	143,000
Accrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Troubled debt restructured loans, balance	$ 3,600,000	$ 3,707,000	$ 3,600,000	$ 3,707,000

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