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Financial Instruments with Off-Balance Sheet Risk (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Commercial lines of credit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loan commitments and standby letters of credit, off-balance sheet	$ 224,370	$ 216,774
Revolving home equity lines
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loan commitments and standby letters of credit, off-balance sheet	177,678	148,143
Undisbursed construction loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loan commitments and standby letters of credit, off-balance sheet	35,322	44,798
Personal and other lines of credit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loan commitments and standby letters of credit, off-balance sheet	11,758	10,635
Standby letters of credit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loan commitments and standby letters of credit, off-balance sheet	4,074	1,939
Total commitments and standby letters of credit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loan commitments and standby letters of credit, off-balance sheet	$ 453,202	422,289
Percentage of commitments expiring in 2018	44.00%
Percentage of commitments expiring between 2019 and 2025	41.00%
Percentage of commitments expiring 2026 and thereafter	15.00%
Total commitments and standby letters of credit | Interest Payable and Other Liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Allowance for off-balance sheet commitments	$ 958	$ 899

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Loan Commitments And Standby Letters Of Credit, Percentage Expiring, After Year Eight

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