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Derivative Financial Instruments and Hedging Activities - Information on Derivatives (Details) - Fair value hedge $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($) derivative	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)
Derivatives, Fair Value [Line Items]
Net hedge ineffectiveness gain (loss), derivatives	$ 51	$ 6
Interest income
Derivatives, Fair Value [Line Items]
Increase in value of designated interest rate swaps due to LIBOR interest rate movements recognized in interest income	529	111
Payment on interest rate swaps recorded in interest income	(55)	(98)
Decrease in value of hedged loans recognized in interest income	(576)	(113)
Decrease in value of yield maintenance agreement recognized against interest income	(4)	(4)
Net loss on derivatives recognized against interest income	(106)	$ (104)
Designated as hedging instrument
Derivatives, Fair Value [Line Items]
Accrued interest on swaps	$ 7		$ 8
Designated as hedging instrument | Interest rate swap
Derivatives, Fair Value [Line Items]
Number of derivative instruments | derivative	5
Designated as hedging instrument | Interest rate swap | Other assets
Derivatives, Fair Value [Line Items]
Interest rate contracts notional amount, Asset derivatives	$ 9,171		4,019
Designated as hedging instrument | Interest rate swap | Other liabilities
Derivatives, Fair Value [Line Items]
Interest rate contracts notional amount, Liability derivatives	9,429		14,810
Designated as hedging instrument | Interest rate contract | Other assets
Derivatives, Fair Value [Line Items]
Interest rate contracts fair value, Asset derivatives	239		74
Designated as hedging instrument | Interest rate contract | Other liabilities
Derivatives, Fair Value [Line Items]
Interest rate contracts fair value, Liability derivatives	$ 376		$ 740

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