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Derivative Financial Instruments and Hedging Activities - Narrative (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) derivative	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Fair value hedges:
Interest rate contracts fair value, Asset derivatives	$ 74	$ 55
Interest rate contracts fair value, Liability derivatives	740	933
Fair value hedge
Fair value hedges:
Net hedge ineffectiveness gain (loss), derivatives	31	113	$ (80)
Fair value hedge | Interest income
Fair value hedges:
Increase in value of designated interest rate swaps due to LIBOR interest rate movements recognized in interest income	212	778	280
Payment on interest rate swaps recorded in interest income	(333)	(556)	(918)
Decrease in value of hedged loans recognized in interest income	(166)	(571)	(308)
Decrease in value of yield maintenance agreement recognized against interest income	(15)	(94)	(52)
Net loss on derivatives recognized against interest income	(302)	(443)	$ (998)
Fair value hedge | Designated as hedging instrument
Derivatives, Fair Value [Line Items]
Derivatives, accrued interest, interest rate swaps	$ 8	13
Interest rate swap | Fair value hedge | Designated as hedging instrument
Derivatives, Fair Value [Line Items]
Number of derivative instruments | derivative	5
Interest rate swap | Fair value hedge | Designated as hedging instrument | Other assets
Fair value hedges:
Interest rate contracts notional amounts, Asset derivatives	$ 4,019	4,217
Interest rate swap | Fair value hedge | Designated as hedging instrument | Other liabilities
Fair value hedges:
Interest rate contracts notional amount, Liability derivatives	14,810	15,495
Interest rate contract | Fair value hedge | Designated as hedging instrument | Other assets
Fair value hedges:
Interest rate contracts fair value, Asset derivatives	74	55
Interest rate contract | Fair value hedge | Designated as hedging instrument | Other liabilities
Fair value hedges:
Interest rate contracts fair value, Liability derivatives	$ 740	$ 933

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