Derivative Instruments and Hedging Activities - Fair Value Hedges (Details) - Fair Value Hedging - USD ($) $ in Thousands		3 Months Ended	12 Months Ended
		Mar. 31, 2018	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gross notional amount outstanding		$ 5,333	$ 5,458
Derivative liability fair value in other liabilities		$ (61)	$ (101)
Weighted-average interest rate received		3.69%	3.38%
Weighted-average interest rate paid		5.96%	5.96%
Weighted-average maturity (in years)		7 months 7 days	10 months 2 days
Fair value of derivative	[1]	$ 70	$ 110

[1] This amount represents the fair value if credit risk related contingent features were triggered.