Derivative Instruments and Hedging Activities - Narrative (Details)	12 Months Ended
	Dec. 31, 2017 USD ($) instrument	Dec. 31, 2015 USD ($)	Dec. 31, 2016 USD ($)
Derivative [Line Items]
Loans receivable with fixed rates of interest maturity period		10 years
Loans receivable with fixed rates		$ 29,100,000
Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional Amount	$ 19,224,000		$ 19,993,000
Derivative Assets	13,000		0
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional Amount	132,593,000		107,448,000
Derivative Assets	$ 588,000		1,058,000
Interest Rate Swap [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Loans receivable with fixed rates of interest maturity period	15 years
Derivative fixed interest rate	7.43%
Notional Amount	$ 523,000		622,000
Loans receivable fixed interest rate (percentage)	7.43%
Interest Rate Swap [Member] | Not Designated as Hedging Instrument [Member] | One-Month LIBOR [Member]
Derivative [Line Items]
Derivative spread on floating rate	2.24%
Interest Rate Swap [Member] | Not Designated as Hedging Instrument [Member] | Other Assets [Member]
Derivative [Line Items]
Derivative Assets	$ 0		0
Interest Rate Swap [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Derivative asset notional amount		$ 20,000,000.0
Derivative fixed interest rate		2.10%
Interest rate cash flow hedge gain (loss) to be reclassified during next 12 months	62,000
Interest Rate Swap [Member] | Cash Flow Hedging [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional Amount	17,836,000		18,566,000
Interest Rate Swap [Member] | Cash Flow Hedging [Member] | Designated as Hedging Instrument [Member] | Other Assets [Member]
Derivative [Line Items]
Derivative Assets	$ 13,000		0
Interest Rate Swap [Member] | Fair Value Hedging [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Loans receivable with fixed rates of interest maturity period	10 years
Derivative fixed interest rate	5.83%
Notional Amount	$ 1,388,000		1,427,000
Loans receivable fixed interest rate (percentage)	5.83%
Interest Rate Swap [Member] | Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | One-Month LIBOR [Member]
Derivative [Line Items]
Derivative spread on floating rate	3.50%
Interest Rate Swap [Member] | Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Other Assets [Member]
Derivative [Line Items]
Derivative Assets	$ 0		0
Credit Risk Contract [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional Amount	$ 75,622,000		27,919,000
Derivative number of instruments held | instrument	15
Credit Risk Contract [Member] | Not Designated as Hedging Instrument [Member] | Minimum [Member]
Derivative [Line Items]
Derivative remaining maturity	1 year
Credit Risk Contract [Member] | Not Designated as Hedging Instrument [Member] | Maximum [Member]
Derivative [Line Items]
Derivative remaining maturity	10 years
Credit Risk Contract [Member] | Not Designated as Hedging Instrument [Member] | Other Assets [Member]
Derivative [Line Items]
Derivative Assets	$ 0		$ 0
Credit Risk Contract [Member] | Not Designated as Hedging Instrument [Member] | Other Liabilities [Member]
Derivative [Line Items]
Underlying derivative at fair value	$ 36,000