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Derivative Financial Instruments and Hedging Activities - Information on Derivatives (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($) derivative	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) derivative	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Derivatives, Fair Value [Line Items]
Carrying Amounts of Hedged Assets	$ 17,651		$ 17,651
Cumulative Amount of Fair Value Hedging Adjustment Included in the Carrying Amount of the Hedged Loans	(493)		(493)
Fair value hedge | Interest income
Derivatives, Fair Value [Line Items]
Increase in value of designated interest rate swaps	222	$ 25	939	$ 7
Payment on interest rate swaps	(32)	(76)	(127)	(261)
Decrease in value of hedged loans	(231)	(43)	(924)	35
Decrease in value of yield maintenance agreement	(4)	(4)	(11)	(11)
Net loss on derivatives recognized against interest income	(45)	$ (98)	(123)	$ (230)
Fair value hedge | Designated as hedging instrument
Derivatives, Fair Value [Line Items]
Accrued interest on swaps	$ 4		$ 4		$ 8
Fair value hedge | Designated as hedging instrument | Interest rate swap
Derivatives, Fair Value [Line Items]
Number of derivative instruments | derivative	5		5
Fair value hedge | Designated as hedging instrument | Interest rate swap | Other assets
Derivatives, Fair Value [Line Items]
Interest rate contracts notional amount, asset derivatives	$ 8,988		$ 8,988		4,019
Fair value hedge | Designated as hedging instrument | Interest rate swap | Other liabilities
Derivatives, Fair Value [Line Items]
Interest rate contracts notional amount, liability derivatives	9,156		9,156		14,810
Fair value hedge | Designated as hedging instrument | Interest rate contract | Other assets
Derivatives, Fair Value [Line Items]
Interest rate contracts fair value, asset derivatives	436		436		74
Fair value hedge | Designated as hedging instrument | Interest rate contract | Other liabilities
Derivatives, Fair Value [Line Items]
Interest rate contracts fair value, liability derivatives	$ 163		$ 163		$ 740

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